Are there any gunsmiths out there who have had a reasonable amount of experience in investigating the possible causes of rifle �blow up�? If there are, I would be grateful if you could give me some pointers on how one might determine whether damage that occurred to a rifle upon firing was due to grossly excessive pressure, or to a case head failure at normal and acceptable pressure.

I have a 6mm Remington built on a �hybrid� M17 Enfield action � a Winchester receiver and an Eddystone bolt. It has had about 200 shots through it since the new barrel was fitted.

Last time I fired it, I first shot two five shot groups with what should have been � and what certainly appeared to be � moderate loads. I then put the rifle aside for a short while to let the barrel cool down. The next load I fired consisted of a 100gr Sierra SP, moly coated (as all the previously fired 100 or so bullets were) over 42grs of H4350. The cases were Norma 7X57, re-formed to 6mm Remington, and lightly neck turned, to give a neck clearance of 0.002� all round. The cases had been fired once before, with a moderate load � a 70gr bullet over 40grs of Varget. (I had previously shot some of the same 100gr Sierra bullets, un-coated, over 41grs of H4350, with no signs of excessive pressures)

On the first shot with the 100gr Sierra load this day, all hell broke loose. The rifle kicked like a mule, the extractor fractured ahead of the circlip and the rear part of it was blown 20 feet across the firing line (nobody there, luckily!) the magazine box, follower and floor plate were blown out, and the stock split in three places. The bolt stop/ejector was left jammed open.

When I recovered from the shock of all this, my first thought was that I must have done the unthinkable, and used the wrong powder. However, when I broke down the remaining cartridges, they all contained 42grs of what was unmistakably H4350. I had only loaded ten of them, to check that load for accuracy, and I simply cannot believe that I could have put the correct powder in nine of them, and something else in the tenth. When I am reloading, I am very careful to only ever have one can of powder on the bench at a time, to avoid any mix-ups. (all the charges were weighed, they were not thrown from a powder measure)

I took the rifle � or the remains of it - to the gunsmith who fitted the new barrel, expecting that he would have to unscrew the barrel the get everything apart and get the case out of the chamber. However, he put the barrelled action in a soft padded vice, tapped the bolt handle upwards with a small rawhide mallet � quite lightly � and it lifted. A few rearward taps with the mallet, and the bolt came back, exposing a badly blown case head and the remains of the extractor. (the circlip which holds the extractor on the bolt had broken off at both ends, so he removed the bent-back ends of that before trying to open the bolt)

He then ran a cleaning rod in from the muzzle, bumped it with the palm of his hand, and the case came out. The case head was a blood-curdling sight. What had been the unsupported part of the case head was horribly swollen, and the portion beside the extractor slot in the breech had been blown off, but the detached piece had been contained by the front portion of the extractor, which was still in place. (sort-of!)

The bolt could then be opened and close quite freely. After all the powder residue, etc was cleaned off the bolt, it was carefully examined, and there was no sign of any cracking or setting-back of the locking lugs. There was no �notchy� sort of feel on closing the bolt, which might suggest some setting back of the lug abutments. Checks with a set of headspace gauges indicated an increase in headspace of 0.002� to 0.003� maximum, assuming that the headspace was previously dead-on.

I have left the rifle with the gunsmith so that he can unscrew the barrel and check the lug abutments and the receiver ring, etc for damage. A superficial examination of the barrel revealed no signs of bulging or any other symptoms of a barrel obstruction. The bullet from the shot that did all the damage reached the target, and cut a round hole, albeit about 8 inches below the point of aim. The previous ten shots all landed in two acceptable sized groups, about on point of aim, so it is pretty certain that there was not some remnant of the last-fired bullet stuck in the bore.

I suppose an insect (an armour-plated one at that!) MIGHT have crawled into the bore during the ten minutes or so that the rifle was standing muzzle-up in the rack at the back of the covered firing line, cooling down, but this is too improbable to be seriously considered.

Question:
Is this damage symptomatic of grossly excessive pressure, or of a defective case head? My gunsmith was reluctant to guess at the cause. How might it be determined, if at all?

If the pressure was excessive, I am at a loss to explain how or why. If this was in fact the cause, I would have expected the bolt to be a lot more difficult to remove from the receiver than it was, and I would also have expected to find the fired case pretty well �frozen� into the chamber, which it wasn�t. I am getting out of my depth here, but from what I have heard and read on this subject, gross over-loads fired in bolt action rifles, producing pressure far above that of proof loads, usually result in a significant increase in headspace, up to ten times or more greater than what appears to have occurred with my rifle.

On the other hand, if the cause was a very soft case head, why didn�t it give way on the first firing? That first load fired in it - a 70gr bullet and 40grs of Varget - is not listed as a maximum load in any manual that I have seen, but it is not a �squib� load, either.

I doubt that doing a hardness test on the remains of the case web would reveal much, because it has probably been work hardened by the severe stretching that took place. Would a hardness test of part of the case wall immediately in front of the web, where it was fully supported by the chamber during firing, reveal anything useful?

Any suggestions � preferably from professionals with first-hand experience of investigating such incidents � would be gratefully received.

Did you visually check the powder level in all the cases before seating the bullets?

redrover---

A big part of my life is in firearms investigations.

From your description I believe you had a a tight neck in combination with a barrel that had the safety breech section cut at the wrong angle and/or an improper extractor slot.

The possibilities that border on remote are soft brass, oversized flash holes, and a cleaning rod down the bore.

If you could send some good close-ups, especially of the brass, I can probably come much closer to an accurate reason for the failure.

The action did what it was supposed to do. It expended it's energy in tearing up parts and not the shooter. Did you have eye protection?

Redrover: You did not mention what primer you used in your load. What was your anticipated gain from using the tight neck clearance? There is a condition called S.E.E. Secondary Explosion Effect, an elusive combination of events aided and abetted by at least 2 of the things you say you did and this is one of those anomolies that is dismissed by probably half of the punditry to the status of "old wives" or Fairy tale. Inasmuch as a similar event occured locally with a 243 on a Turkish made mauser, about same wt bullet, 2 years back, there was a rash of these things almost 40 years ago and circumstances too close to rumors of these two events, to simply dismiss as (individually) "just one of those things". In checking with my usual sources at the Mauser/243 surprise the rumor mill indicated that several events with 6m/ms had occurred a year previous to this one (2000). The loads were intended for reduced range ground squirrel reduction. The shooters had no social relationship with each other. Were the Norma cases full length sized before the neck turning? If not, Why not?

Jack B. About a week ago I sent you an E mail about Pressure step thresholding. Do you call this Prescience? I had just moved the bolt and part of the brass spelter while in process of dusting off the window sill where it resides that caused me to write you. I think that it is time. Concur ?

P17 & reformed cases. Sounds familiar. Holy crap, you were lucky there was no one else at the range when this happened. Next time I see a P17 at the range, I think I will watch him shoot from a looong ways away.

Sorry for showing this piture so many times, but this is what happened when I necked 308 brass down to 243 and some necks pinched more than others.
The loads were all 40 gr IMR4895 and 100 gr bullets.

redrover,

You mentioned "The rifle kicked like a mule", it's a sign of high pressure, not a weak case. A weak case that ruptures will not increase the recoil, and if possible, actually lowers it due to leaked gas and lowered pressure.

Like JBelk said you have a tight neck in the chamber. I think that welcomes mishaps.

I have some questions :

1. Did you make sure the bullets are not seated "into" rifling lands or just on the lands?

2. Is the chamber a custom, tight chamber?

3. Is the case full-length sized after the first firing?

4. Is the 100-grain Sierra SP seated deep that the neck portion of the case is in full contact with the bullet?

5. Are the neck-turning done from outside or inside the neck?

If your answer to 3, 4 are both yes then I think I can tell you what happened, ruling out moly and ladybugs as cause of problem...

Pyrotek

[ 05-11-2003, 08:27: Message edited by: Pyrotek ]

Tom--

I sure do concur. I think it's a dark place in a process that seems to be understood but sometimes gives mysterious results. More information has to be the key.

redrover---

I'm curious about your chamber dimensions. You say you're resizing 7x57 brass then turning to give .002 neck clearance.....

That means you have a tight necked chamber? Normal is .275 or so.....factory ammo is what? .270 at the neck? (give me a break, it's memory! ) Benchrest necks are usually .262 or there 'bouts. What's yours?

The VERY first thing that comes to my mind is the wrong powder. I understand how you discount it and I belive you, but it's hard to see another "for sure......maybe" reason for what happened.

Your comment about recoil points to a definite pressure spike. When a case fails the noise is like being struck by lightning, but recoil is surprisingly light. (don't ask how I know about either one.)

You didn't mention hard bolt *closure*. If the neck had thickened or the bullet was canted the bolt would have been stiff in closing. That's always a danger sign we all tend to ignore.

I assume you didn't somehow anneal the entire case........

What did the primer pocket look like??

Where did the case fail? The head must have still been on it since the GS knocked it out with a rod. Where did all that gas come from??

It stands to reason either the case failed at normal pressure OR there was excess pressure. Some good close-ups will tell which. That'll simplify the process some.

Can you describe how the caliber markings look on the blown case as compared with a normal one?? That would help too.

t_bob38:

I can�t say that I specifically remember checking the powder levels in all the cases, but I�m sure that I would have � it�s just an automatic part of my procedure. Once, nearly forty years ago, at the beginning of my reloading experience, I did omit to charge some cases � missed a whole row of four in the loading block by the look of it. Fortunately this error came to light on the range, not in the field, and the consequences were not dramatic. The primer didn�t develop enough pressure to even start to shift the bullet out of the case. It taught me a lesson, though � I�ve have always checked powder levels since then, and I have never repeated that booboo.

Mr Belk:

A tight neck is definitely not the cause. The reamer specification is a 0.277� diameter neck, and the mouths of cases fired in it generally come out at 0.276� to 0.2765� when they have been loaded with 87, 90 or 100gr bullets and slow burning powder. (H4350 or H4831) I have noticed that when the load is a 70gr bullet over a charge of Varget, they usually don�t blow out quite as much, and it is only just possible to pass a bullet through them, and sometimes not at all. But when the very same cases are loaded with heavier bullets and slower powder, they expand fully.

All the cases in the lot I was using when the trouble occurred measure 0.2725� over a seated bullet. The portion of case �X� (the troublesome one) ahead of the web is fully intact and normal looking. The mouth has not expanded fully, measuring about 0.275� in diameter, but it is still just possible to pass a bullet through it. When I neck turned this lot of cases, I was getting about 80 to 90% clean up on most of them. Case �X� definitely got its neck turned, because a small segment which the cutter did not touch is still quite visible. It was only on its second firing, and the difference in texture between the turned and un-turned parts is still quite obvious.

I can�t really comment on the matter of the angle if the breech and the extractor slot, except to say that it appeared normal to me, just looking in through the action.

I doubt that an incorrectly cut extractor slot could be the answer. I�ll have to go back on my statement that part of the case head blew into the extractor slot, because I have since noticed something about the case head that I had missed the significance of previously. At one side of the blown-away part of the head, there is a tell-tale, rectangular ridge, 0.085� wide and about 0.025� high. I can now see quite clearly that this was formed by part of the case head extruding itself into the ejector slot in the left (top when closed) locking lug. Therefore the part of the case head which was blown away was at the upper left quadrant of the chamber � looking from the rear - when it was fired, not the right side as I said previously.

Half of the case head is still (sort-of!) intact, and roughly a quarter of it was blown off. The edge of the break nearest the left lug is relatively sharp, but there is a lot of tearing and distortion at the other edge, extending over all the lower-left quarter. Over the half of the head which must have been at the right side of the chamber, the unsupported part of the head is bulged out approx 0.025� from the case wall. The (approximate) half of the head which remains has a radius of about 0.250� (0.500� diameter, if it was all there) and the remaining half of the flash hole has a radius of about 0.045�. (0.090� diameter, if it was all there, which it is not)

It is therefore clear that the head has expanded considerably all round, not just at the one section which blew out. The swelling starts about 0.18� up from the base of the case, at a line which appears to be just above the inside face of the web, and reaches maximum diameter at about 0.11� up from the base. I hope this does not mean that there was a breech gap of 0.18� � that sounds far too much.

However, even if the breech gap was on the large side, there must have been something very wrong with cartridge �X�. The rifle had previously fired at least 200 shots, some with the re-formed Norma 7X57 cases, and some with factory Norma 6mm Remington cases, without any problems. (except that accuracy with the heavier bullets was a bit disappointing, which is why I was still trying out various different loads)

There was definitely not a cleaning rod in the barrel when I fired the destructive shot. I didn�t even have a rod with me that day, and there was nobody else at the range at the time who might have put one there � I had the place all to myself. Besides, as I said before, a new, clean round hole appeared in the target after I fired that shot.

I can�t swear that I had inspected every single flash hole of those hundred 7X57 cases, but there is a fair chance that if one was significantly oversize I would have noticed it. I had handled the cases a number of times, what with necking them down to 6.5mm, full length sizing them to 6mm Rem, neck turning them, wiping them outside and in the necks to remove lube, and then priming them. That was just for the first firing. I neck sized them and cleaned the primer pockets for the second firing, so that would have given me yet another look at the flash holes.

Soft brass? I don�t know, but I wish I did.

I�m not really into photography, except for snap shots with an automatic camera, so I�ll have to enlist some expert assistance to get some useful close-ups of the case. I�ll see what I can do, and get back to you on this one. Thanks for the offer of further assistance.

Yes, the action basically did as it should have in the circumstances. I have read some opinions that the Enfield is not particularly good at handling escaping gas and debris, but next to nothing came �out the back� of this one. I collected two minute, pin-prick size wounds on my right cheek from whatever it was that did escape. I was wearing glasses with quartz-coated plastic lenses (I think that was what the optician called them, or something like that) and my eyes are undamaged. There wasn�t even any noticeable debris left on the lenses.

I stated previously that �the rifle kicked like a mule� on the shot that did the damage, which may not be entirely accurate, but the recoil was certainly DIFFERENT. I was shooting off a bench, using a benchrest type front rest and a rear sand bag, with the butt on my shoulder, and not holding any part of the fore end. I had tried shooting that rifle �free recoil� (i.e. no shoulder contact) but I found that it came back hard enough to hurt, so I soon gave that up. I shoot for enjoyment, not to knock myself around! As I fired the damaging shot, the rifle slid down off my shoulder and the ocular lens cone hit my right cheek about level with the bottom of my nose, making a painful cut which bled like a broken tap and didn�t stop for ages, and my cheek instantly swelled up like half a tennis ball. That may have made me think the recoil was more than it actually was. I can�t be too sure � it all happened very fast, and the aftermath was so appalling that my recollections of that fraction of a second might not be 100% accurate.

I have been writing all this �off line� and have just now looked back at the forum and found that there are five new postings on this topic. It�s in the small hours of the morning here, and I�m ready for some sleep, so I�ll post what I have written this far and answer the rest of the questions tomorrow.

Thank you all for your interest and suggestions.
Red

I have dabbeled with tight necks and still do in the benchrest and 1000 yard guns.

I am concerned:

You say the chamber is 0.277" neck. And the loaded rounds are 0.276" to 0.2765".

This is IMHO too tight. Throw in a little misread of a mike, and high pressure raises its ugly head.

0.002" total clearaance over a neck turned loaded brass is considered tight. Anything less and you must tread with caution. We have fooled with 0.001" total clearance, real risky, everything has to be absolutely perfect. And your 0.0005" clearance (this is one half of a thou) IMHO is real, real risky, especially in Enfield type chamber. Tight neck chambers, and cartridges that may explore higher pressures, do not belong in an Enfield.

You say the chamber is 0.277" from the chamber drawing. Do you know the chamber is 0.277"? With tight necked reamers, I always make up a short stub, from a piece of barrel, and run the reamer in just so all of the shoulder is chambered. Makes a nice bullet seat gauge, and the neck is easy to measure. I measure the actual neck cut by a tight neck reamer, one, as it is impossible to measure the neck on a reamer with a mike due to the staggering of flutes, and two, to be sure the reamer maker did indeed attain the correct dimensions. Also, I do not trust one mike, I use several, all read to tenths and one is a digital. If your mike will not read to tenths, you already are in trouble. And a heavy hand on the thimble will put you into trouble big time.

Throw in a little over length of the case, with a tight chamber neck, and you have a bomb. Do you know where the end of the case neck is in the chamber? Might be real close to runing out of room.

You have to measure the neck of each loaded round with a GOOD micrometer, used properly.

And you should have a tubing mike, to measure the necks as you turn them. Measure each in several places. An improperly used neck turner will result in varying neck thickness around the neck.

Another thing: I have seen powder hang up in a powder measure, this occured when the gent was emptying and changing powder. He did not dismount the measure from the stand and take a good look. Guess what, when he put in another type of powder, and was adjusting the charge, he threw a pan full of mixed powder. Only thing that saved him was one powder was stick, the other was ball.

I did not go back and read your lengthly postings, but are you measuring each charge with a scale, or setting the measure and charging the cases with the measure?

[ 05-11-2003, 19:14: Message edited by: John Ricks ]

John Ricks,

The 0.2765" neck is from a fired case, the unfired ones are said to be 0.2725".

redrover,

What I suspect is that the cases are full length sized and some part of thicker brass at shoulder area have moved forward into the neck. The base of the neck thickened but did not get neck turned again. When the second loading is fired the neck of brass fits too snugly and caused the blow-up. Just to rule out another factor : did you trim the cases to within safety limits?

Pyrotek

For a quick check on neck size/ length problems see if a bullet will enter the mouth of the case that "blew". A thick neck, or a too long case will prevent the bullet from leaving.
This is what blows up a 30/06 with 8x57 ammo (the ones that will chamber it). It isn't the larger bullet, but ther fact that the neck can't open.
Good luck1

In response to the further questions asked:

Mr Burgess:

The primers were standard Winchester large rifle, silver coloured, from a white box. I bought 2000 of them about two years ago, and have been using them in at least six different rifles without incident.

I don�t know that I would describe 0.002� clearance all round (i.e. case neck diameter over a seated bullet 0.004� less than chamber neck diameter) a tight neck. The Norma 6mm Rem factory cases I have are barely 0.001� smaller in neck diameter. (loaded, that is) I have three 6mm Rem sizing dies, a Lyman F/L die, a Redding F/L die, and a Lyman neck sizing die (an old Tru-Line Jnr job) and they all size my case necks down to 0.266� or less in diameter, and then expand them back up again to about 0.270� to 0.271� depending on which lot of cases. I�ve got a Redding Type S neck die on order, along with a 0.269� and a 0.270� bushing, to avoid working the brass excessively.

I have certainly heard of SSE, but most of the stories about it seem to involve very light charges of very slow burning powders � like half charges or less of 4831, and other even slower powders. As I said in my previous reply, I�m pretty sure all my cases had the right quantity of powder in them. It would, I think, be quite difficult to make a really gross error with weighed charges.

I believe I MAY have witnessed a case of SSE about thirty years ago. A chap on the range was shooting a Sako L61 in 30-06, using 150gr bullets and about 58grs of the old WWII surplus H4831. Not an ideal combination, but 4831 was cheap and readily available here in those days, and it apparently worked OK. He had fired quite a number of shots without incident, then suddenly his rifle blew up in much the same manner as my Enfield.

His anguished claim was that it must be IMPOSSIBLE to get enough 4831 into a 30-06 case to create excessive pressures with 150gr bullets, which is probably true. When we checked his remaining ammo, we found that with most cartridges you could not hear any powder rattling around inside the cases when they were shaken, but with a few, you could. With the aid of a Heath Robinson bullet puller (a pair of pliers out of somebody�s car toolkit) we got the bullets out of a couple of the latter rounds, and found that they were less than half full of powder. The shooter admitted that he had thrown all the charges with a powder measure (always risky with coarse grained powder, in my opinion) and that he had probably not made a visual check on the powder levels in the cases. You can draw your own conclusions.

To return to your questions, yes, the cases WERE full length sized before they were neck turned. As stated in my previous posting, the sequence was to run the necks down one step in a backed-off 6.5X55 die, set to size the neck down to just a fraction short of the shoulder, lube the cases again and run them into the 6mm Rem F/L die, then outside neck turn them. They all went through their first firing without any problems whatsoever.

todbartell:

I�m not sure what point you are trying to make. The Enfield actions would not win any prizes for being the world�s strongest, but they are hardly weak, either. Look at the number of big magnums which have been built on them without any problems. I don�t see any particular problem with using re-formed cases, either, if they conform to specifications. My 6mm cases did. I carefully set up the F/L die to ensure a close head to shoulder fit in the chamber, the finished overall length of the cases was 2.225�, which is 0.008� shorter than nominal length, and the diameter of the necks, over a seated bullet, was 0.004� less than the chamber neck diameter.

Pyrotek :

Regarding your questions:

> 1. Did you make sure the bullets are not seated "into" rifling lands or just on the lands?

Yes, I made VERY sure that they were clear of the lands, with all the loads I have shot. I have no use for ammo that might leave me with a bullet stuck in the lands and an action full of spilled powder if I have to extract an unfired cartridge. If doing this does happen to sacrifice a tiny bit of accuracy, so be it.

> 2. Is the chamber a custom, tight chamber?

No, it�s a standard SAAMI spec. chamber. Fired cases measure 0.276/0.2765 at the mouth. 0.431 at the shoulder, and 0.471 at the expansion line.

I have also weighed a fair sampling of all the cases I have used. The Norma factory 6mm Rem cases weigh 171 to 173grs (empty) the reformed 7X57 cases 174 to 175grs, and some second hand Winchester cases (which I have not actually fired) weigh 169 to 171grs.

> 3. Is the case full-length sized after the first firing?

No, they were neck sized only.

> 4. Is the 100-grain Sierra SP seated deep that the neck portion of the case is in full contact with the bullet?

I�m not sure that I understand your question. The necks were re-sized for about 2/3 of their length. At the seating depth of the 100gr Sierra bullets, their bases were about level with the neck/shoulder junction of the cases. There are no �donuts� at the base of the necks of the cases causing a pinching action on the bullets.

> 5. Are the neck-turning done from outside or inside the neck?

Neck turning means removing the metal from the outside. Removing metal from the inside is neck reaming. At least that is how I have always understood the definitions.

Mr Belk

I have to agree with you that this case (pun intended) does have symptoms of a gross over-load, though I can�t understand how. The only powder other than H4350 I had been using around the time I loaded those cases was Varget, and that is definitely not what I found in the remaining nine cartridges that I broke down. The colour is similar, (to me, but I�m half colour blind) but the grain size is slightly different. I have compared them with an 8X jewellers loupe, a small 100X microscope, and also miked the kernels.

The other question that occurs to me is that even if I did somehow put Varget in that one case instead of H4350, would 42grs of it under a moly coated 100gr bullet be capable of causing all the mayhem? It would certainly be an over-load, but hot enough to do all that damage with a properly made case????

At one stage I tried some 90gr Lapua Mega bullets with various powders, and went up as high as 38grs of Varget behind them (plain, un-coated bullets) with absolutely no discernable signs of excessive pressure. Accuracy with those bullets was always lousy, with every powder and seating depth tried, so I gave up on them.

> You didn't mention hard bolt *closure*. If the neck had thickened or the bullet was canted the bolt would have been stiff in closing. That's always a danger sign we all tend to ignore.

Bolt closure was dead easy with the re-formed 7X57 cases, and with the 40 Norma factory 6mm Rem cases I have, which are on their fifth loading, and which have only ever been neck sized. (when I add all this up, the new barrel has had over 300 shots through it, not 200 as I said before) The rifle has a Dayton-Traister cock on opening kit in it, and it operates very smoothly indeed. An even slightly sticky case would have been quite obvious.

> I assume you didn't somehow anneal the entire case........

I hadn�t annealed ANY part of them. The 7X57 necks reformed easily, so there didn�t seem to be any need for it. I certainly intended to do so if the necks started splitting on firing, but I didn�t get to that point.

> What did the primer pocket look like??

I don�t know that I can add a lot more to my description of the blown case given in my posting dated 17:31hrs on 5-11-2003, but I�ll try. There was a clean break across the middle of the bottom of the primer pocket, running across from the ridge formed by brass flowing into the top lug slot. About a quarter of the brass that broke away from the bottom of the pocket was still attached to the part of the head that ripped away by where the lower lug would have been. The other quarter of the head and primer pocket was completely ripped off.

There was, therefore, about half the web still intact, and the jag on the end of the cleaning rod the gunsmith used to push the case out caught on this. As I said, the case came out quite easily � just a light bump with his palm on the handle of the rod.

> Can you describe how the caliber markings look on the blown case as compared with a normal one?? That would help too.

The stamping of the word �norma� was between about 1:30 and 4:30, as the case lay in the chamber on firing. That portion of the rim looks very slightly peened over near the edge, as though the case tilted slightly to the left on firing. The stamping does not appear to have diminished significantly in depth.

It�s hard to describe it all exactly � I�ll have to get some good quality, close up photos to give you the full story.

Mr Ricks:

You have mis-read the dimensions I have stated.

To reiterate, the chamber neck is supposed to be 0.277�, the necks of fire cases usually measure 0.276� to 0.2765� on my Mititoyo mike. It is a 0 � 1in model, reading directly to 0.001� with a vernier on the barrel reading to 0.0001�. I�m not a professional gunsmith or machinist, but I do know how to take at least consistent measurements with a mike. I periodically check this mike against my Mititoyo 0 �25mm mike, which reads directly to 0.01mm, and they have always agreed.

I have had chamber casts made for some of my rifles, and my experience has been that the necks of cases fired with full loads usually measure about 0.0005 to 0.001 smaller than the chamber neck diameter. This tallies with what I have experienced with the 6mm Rem. I had hoped to have a cast made of the chamber of this 6mm Rem, but the gunsmith had run out of Cerrosafe at the time he did the work on it.

The before and after firing neck diameter measurements were made with the same mike, so whether or not its absolute readings are perfect or a couple of tenths of a thou out, the DIFFERENCE between them is still a good 0.004�. That�s what I work to with Lapua cases in my Sako 6PPC, which works well, and is tight as I want to go with any rifle, unless I take up BR. (which is highly unlikely)

Believe me, I was NOT intending this rifle to be a �load �em up to the max� machine. It�s not my philosophy with any rifle, and all of the loads I have fired in this one were under what various manuals list as maximum. It�s accuracy I want, and reasonable case life, not the last little bit of attainable velocity.

As stated above, the length of the re-formed 7X57 cases is 2.225� give or take a thou or so, which is comfortably under the nominal case length of 2.233�. As also stated previously, the charges were ALL weighed, not thrown from a powder measure.

Pyrotek:

The cases in use when the blow-up occurred were on their second firing. They were new cases which had been full length sized and neck turned prior to the first firing, and neck sized only for the second. They do not have any trace of �donuts� at the bottom of the necks.

Donuts are more likely to occur with re-formed cases which have been necked up, not down, though they can crop up with almost any case. The Norma 6mm Rem factory cases I have developed small donuts after the fourth firing. A 6.2mm drill, run into the necks of the fired cases (by hand, with a small tap wrench) removed them neatly, without doing any more than faintly scuff the insides of the rest of the necks. I�ve had the same experience with Norma 6.5X55 cases � pronounced donuts forming after the four or five firings. I run a 17/64in hand reamer run into the fired cases to remove them, and it then takes a lot of firings before they re-appear.

irv:

I did the checks you have suggested at the outset. No problems � see above.

Phew � finally finished!

Thank you all for your suggestions.
Red

Hmmm...If the Accurate Reloading Forums is scaled up into an innocent small town in olden times, the matter we discussed here would be the first murder mystery in centuries...

Strayed from the topic, hope you don't mind. My doubt is clear now and I can't guess what went wrong, I'll leave this to more experienced members. I'll be paying attention however.

Pyrotek

You have covered all the "normal" causes. This leaves you with solving the "funnies".
Could you have had some substance (moly, lube, ect) build up around the case neck?.
Alittle bit goes a long way there.
Like you I have never seen or experienced secondary explosions, but from time to time over the years have heard of this occuring with a .243 and 4350. Who knows for sure?. Your load was not greatly reduced from the max shown in my manual.
The fact that the rifle kicked harder than usual seems to mean that the pressure was high, not that the brass was soft.
If you ever solve this please bring us up to date.
Good luck!

Red, Second run, trashed first. There is enough for 3 related themes in your happening.
You did not really answer My why? questions but it seems as if you were following practices based on an attempt to relate bench resting loading drill to do what "normal" shooters do hoping to tweke a little more accuracy out of their outfits. Well, we have all heard about the road to hell so no need to travel that route.

You evinced surprise at my,and Mr Ricks calling your close tolerance :chamber neck to ctg. neck "tight". Well,it is and very much so in VOLUMETRIC terms. I'm hoping to keep to that theme, only, in this post. You have stated that you neck size and you have minimal diametrical neck clearance. That is 2 out of 3 things that cause the same result you have had. The 3d one is to use Magnum primers. Some times that alone makes 3 for 3. The recent spate of these happenings in my state,3 and 2 years ago involved combinations of the 3, plus reduced loads to be used for rodent control around cattle (Richardson's ground squirrel which lives in burrows).

VOLUMETRIC EXPANSION TOLERANCE

This is the difference in case diameter versus chamber diameter at various points which is utilised to reduce the effect of the inheirent propellant characteristics for each powder and which result in pressure spikes over time and damned near in pico seconds. the first spike can be in the high 90 K psi's ,the next threshold in the mid to low 80 K's the 3d mid to high end 60K's, the 4th at near 55K and the 5th and longest at about 38,000 psi and dribbling off as projectile leaves muzzle. A CUP measurement for a suitable load with all of the above can be 58,000 psi .Not exactly a static rendition, but certainly not DYNAMIC. The duration in time of these peaking spikes is what you have to worry about in setting the course you have followed.

AMMO FACTORY METHOD
6 m/m Rem chamber diameter shoulder MIN. .4314"
REM. avg. ctg diameter at shoulder .425+
but not to exceed MAX. .4295"
REM. avg. headspace difference,ctg, short-.005
from minimum chamber headspace gage.
REM. loaded ctg., typical neck dia.s,
near shoulder beyond radius avg. .273"
at end of case back of crimp .271"
Print minimum dimensions,neck by shoulder.2779"
at end of neck diameter-(Chamber) .277"
MAX. O.A.L. case length 2.233"
MIN. chamber length to 45 deg. reduction to throat diameter. 2.253
Throat dia.-cylindrical to leade angle- .2437"
Length of throat cylinder .118"
Length of leade angle (approx.) .040"

When Winch came out with the .300 Win mag. the new purchasers started to question the gunwriters about the noticable difference between a fired case from an M 70 chamber and a factory round ie.
that very short remaining neck. The answer the writers gave was that obviously you needed more neck to grasp the bullet. That wasn't why. Winchester wasn't about to give Weatherby and his 3/4" long cylindrical section to leade Freebore any advertising leg -up so they reduced the ctg length to shoulder distance on the cartridge by .029" minus to same distance in chamber. No, that is not a missprint!
They also reduced the diameter of the shoulder to give a diameter difference of .009", That plus the typical Winchester continuous angle throat leade( no cylindrical section) gave them the expansion room they needed to reduce the intensity and duration of the pressure spikes and come near to the 300 WBY. cartridge ballistics using much less powder.
With the 7 m/m Rem Mag, Rem didn't have to do that. They were able to persuade "Mother" Du-Pont to make them what we know as IMR 7828 and later some other powders. Olin had not perfected a ball powder to duplicate that and thus there was no 30-338, although it was said that The Lawyers were worried about shooters stuffing .30 dashes into 7 mags. Perhaps.
Bulk lot powders as purchased by Ammo Mfrs are close to but not actually the same as what we buy. The ammo maker can vary the envelope (pressure vessel) to get around unwanted spikes which even if controlled can give too much variation in shot to shot velocity and thus over and short out past 200 M. If you shoot competition
this can leave you out of the win,place or show. It is much more difficult to controll the burning rate of the powder to achieve advertised velocities, So, they control the envelope. Once you get that rifle up and running again there are some tests you might try.

1, Take a primed case exactly prepared as those which caused the problem. It will be short by the .002 increase in headspace, but fire the empty anyway. The primer should stand back from the base by MORE than that .002. Ask yourself why?
You can do the same thing again with no powder but a bullet- same type loaded as you did before the accident. Make sure you have a cleaning rod with you, (bullet might stick in the rifling).
This measurement should be made prior to firing
and again after. You want to meaure the O.A.L. of
case mouth to end of primer. That ammount should be subtracted from the max length for trim as an allowance for drive forward into chamber.

You really do need a chamber cast. You also ought to have a L.E. Wilson style cartridge case headspace gage. Forster has made them and Mid Way has supplied them for a number of years. If that is too much hassle the gunsmith who chambered the rifle can make you one of a piece of barrel stock .They came 1 " in diameter and are simply a dummy chamber. A custom variety would be made so that the fired case base is same highth as the base of the gage,with a lower step .005(-) for the headspace max case. the distance from this lower step can have 3 steps, one for must trim that is Max case less what you found from the primer firing which ever you found greater end to end and a 3d step for reccommended case length.
A full length sizing die should be altered to provide the minimum headspace. This die should reduce the shoulder diameter by at least .005" to chamber and if less, don't sweat it as different brass frequently comes out larger in diameter. Subsequent use of the brass will work harden the metal and it will increase in diameter because of less spring back. All of these dimensions take the spring temper of the brass into consideration. Think about brass musical instruments. Bugles, cornets, trumpets,and trombones The bell on the end is formed on a spinning lathe. The Artist takes a tool called a "spoon" and presses it against the inside of the tube he is working and with muscle power works the brass, flaring its mouth as he goes against a metal form. He must anneal the material from time to time but eventually he gets a shape that is spring tempered and very close to the "Mold" form. The metal thins out in the process. This mold is like the walls of your chamber and the spoon-forming iron- is the high pressure of the gas in the sealed ctg. envelope and can be thought to be every bit as hard and unyielding as that "spoon". If you start out with a case almost tightly conforming to the chamber the gas which is following the base of the bullet acts as a forming iron and works that brass as against an anvil drawing it forward and stretching it in length. The scant bit of volumetric difference between a sized case as from factory or as sized full length must first expand to fit the chamber walls as it is simultaneously overcoming the inertia of the projectile AND THAT TIME IS ENOUGH TO REDUCE THE SPIKES INTENSITY AND DURATION. That pressure remaining should then be below the plasic deformation number for the particular lot and heat treatment of the brass and thus not semi liquify. If you are close to that level it will loosen the primer pockets.( as a warning)
Another experiment you should try. Measure a case for length before full length sizing and again after sizing. In the old days before carbide -lower friction expander balls the case grew by about .007 in length. Changing the die shoulder angles and shape of expander ball brought this down to as low as .003 growth. Funny thing. The neck sizing cult usually ended up trimming more length after their sizing than the full lengthers did when the brass was decent. The 243 brass stretched even more. The donut? Does that get "spooned" off the shoulder or from the body of the case, or maybe from both sources?

Bench rest procedures and needs as they relate to just plain shooters is about the relationship of Golf to Ice Hockey. The effort is to direct a projectile where you want it to go taking in to account a lot of variables and just plain chance and there it ends. Hoping to use a minimal diameter throat and neck to more perfectly align the long axis of a bullet to that of a barrel interior might make sense if the rear end of the case could be controlled also, but funny thing, it isn't all quite that necessary for acceptable accuracy in a hunting rifle. proper Rem type throat tends to align the bullet on its own.

There is a lot more but some of the others will no doubt pile on and what they don't cover I might be able to later. This has been a very long night for me ,too

Tom---

Thank you for a great technical post that explained a lot of what I though I "knew". Great information, said well.

You ARE keeping these post for your book aren't you?

To todbartel: By all means watch from far away. You can even try to argue that the world is flat if you want. It's a free country.

However, the simple fact remains that the 1917 Enfield action is on record as one of the strongest bolt actions of all time, bar none. That action has been successfully used to house the biggest, baddest magnums of all, including the Weatherbys, Dakotas, Rigbys, A-Square, etc.

P-17---

As long as you understand WHY the P-17 is "strong" you're right.

The P-17 is not much different (or stronger) than any action based on the M-98 design......and well made from good material.

The Mauser/Springfield/Enfield/Model-70 system works exactly like a fireworks factory. When things go wrong the roof and walls blows away and berms outside deflect the blast wave up and away from neighboring structures.

Consider the floorplate as being the roof and the magazine box and extractor the walls. When such actions vent their fury it's usually not the shooter that suffers (though Todbartel very nearly lost an eye when his pitched a fit), but the neighbors ARE at risk. His statement of caution is well founded.

BTW-- The Enfields are used for big cases because the action was built too big for the calibers they were manufactured in......NOT because they're stronger than others.

I personally have met two shooters that've lost an eye to a P-17 rifle.

one of us; Could you give the reference for the 17 Enfield being "the strongest by record".
The only tests I know of were Ackleys, he showed it to be somewhat weak. It is massive, but strong?.
Take Care!

Every time I see posts like this, I make a mental note to load my P-14 458 Lott down a little more. A few more, and I might not load it at all!

Todd

The strange recoil was due to the rifle recoiling up from the powder combustion gases exiting via the magazine, rather than pushing back as when normally exiting the muzzle.

As for cause,?? Are you positive that the bolt was completely locked into battery?

Tom, interesting information you put foward. First off let me explain that I'm a toolmaker by trade, so percision is a passion with me, I'm used to splitting tenths. Secound, I'm one of those whom strive for the ultimate accuracy out of my rifles.

What's your definition of acceptable accuracy from a hunting rifle?

Where do you draw the line in procedures used for reloading for hunting use v/s benchrest?

Am I to understand that the reason Remington, for an example with the .300 ultramag, uses long freebore is to allow the bullet time to seek it's alignment, and by altering the freebore may be detrimental to accuracy?

What if loads are used that the bullet runout was eliminated?

With my 300 ultra, I turn the necks to get the O.D.'s and I.D.'s concentric to the body of the brass, trying to eliminate bullet runout. I'm only taking .002" from the neck dia. What would you concider to be the minimum clearance between the neck to the throat dia's?

Sorry for all the questons, you've entered an area that I've been contemplating for a project of mine.

Thanks.

Mr Burgess:

Thank you for your posting dated 12 May 2003. I have read it several times, but it will take me a while to properly chew and digest all that you have written. However, there are a few comments and questions I would like to put to you now.

I thought I had explained previously why I had chosen to neck turn the cases to an outside diameter of 0.2725�. (over a seated bullet, that is) It was simply to minimise working of the necks, nothing more. They have been getting a bit overworked, so far, because the Redding bushing die I have on order has not yet arrived

The chamber in my 6mm Rem rifle was cut with a reamer which Allan, my gunsmith, bought many years ago direct from a maker named Dick Francis. I understand he was reputed to one of the best reamer makers around at the time. It is actually marked 244 Rem, which gives some clue as to its age. Allan says it is probably the best reamer he has ever used, and cuts like a dream. He also says that it has cut very few chambers, because he has had little demand for rifles in that chambering, and it is still as sharp and clean as one could like.

The chamber dimensions you have quoted, and the measurements I have taken on fired cases, tend to confirm Allan�s statement that the reamer is made to standard SAAMI dimensions. (unfortunately, he does not still have the dimensioned drawing of it, but he was clear in his recollection of it having a 0.277� neck) My fired cases measure 0.276� to 0.2765� at the mouth � or rather a very small distance back from it, to miss the light chamfering there � and about 0.001� larger at a position back almost to the shoulder, which tends to confirm this.

You quote a standard cartridge case neck diameter of 0.271�. Presumably this is for the diameter over a seated bullet � it would be quite meaningless if it wasn�t. So the difference between the diameters of a standard chamber neck and a standard loaded cartridge neck is 0.006�. I would surmise are both dimensions are subject to some +/- tolerance, though I don�t know for certain, or how much, because I do not have access to a set of SAAMI specifications.

You go on to say that with my cartridges having a neck diameter of 0.2725� over a seated bullet (0.0015� larger than the standard cartridge neck, or 0.0045� smaller than chamber neck diameter, whichever way you want to look at it) I have created a tight neck situation � �very much so�. I�m still trying to get my head around this one. If this is a dangerous set up, then what seems to be pretty much the standard formula for 6PPC benchrest rifle necks must be positively suicidal!

From what I have frequently heard and read, they most commonly use a 0.262� diameter chamber neck, case neck walls 0.0086� thick, and bullets generally measuring about 0.2433� in diameter at the pressure ring. In other words, the diameter of the loaded cartridge neck is 0.0015� smaller than the chamber neck � ONE THIRD of the clearance I have been using.

I am quite well aware that benchrest rifles would generally be made to closer tolerances than my 6mm Remington, and the reloading equipment used may be better, too, and I am certainly NOT trying to slavishly copy BR practices. However, in respect of the neck and chamber part of things, we are still just talking about a brass case in a reamed chamber. I have every confidence in my gunsmith�s ability to ream a chamber correctly, and I have seen nothing to suggest that mine is eccentric to the bore, out of round, or whatever. (I have seen plenty of examples of his workmanship, and I could easily run out of superlatives trying to describe them)

While I cannot claim to have measured the OD of every one of the 100 case necks which I turned down, I have measured a large proportion of them, over seated bullets. (I don�t own a tubing micrometer) I have just an hour or so ago re-measured the necks of all the cartridges which are currently loaded, and I did not find one which measured over 0.2725� at any part. Some were a tenth or so under if measured across parts where the necks had not been fully cut. I would estimate that the neck turning achieved about 80 to 90% clean-up, on average, and 100% on a few cases.

Could you spell out for me exactly why having case necks 0.0045� smaller in diameter than the chamber neck creates a dangerous situation? I just cannot see it, at least not with the case prep procedures I always follow. There is quite sufficient all-round clearance to allow the case neck to let go of the bullet.

As soon as I can after firing reloadable cases, I clean the insides of the necks with a stiff nylon brush of the appropriate diameter, and the outsides of the cases with some No 9 on a piece of flannelette. When I neck size, I always lubricate the outside of the neck, and the inside as well if I am using a die with an expander plug. Then I clean off ALL traces of lube, outside with isopropyl alcohol on a rag, and inside with a strip of rag folded over the end of a rod of suitable diameter and moistened with IPA.

Sure, all this lubricating and cleaning takes a bit of extra time, but I�m happy to do it and be reasonably sure that I am not leaving significant residue in my case necks or carrying dirt and stuff into my chambers or reloading dies. A an aside, I have checked MANY times for case lengthening due to using an expander plug in resizing dies, but with the case necks lubed, I have seldom, if ever, found any clearly measurable increase. Gradual increases in length on repeated firings, yes, definitely, but next to nothing from neck resizing and expanding alone.

I am also struggling to draw a conclusion from some of your comments about neck sizing versus full length sizing.

Are you saying that one could fire a new or full length sized case with a certain load which generates high, but entirely acceptable pressure, then neck size the same case, reload it with exactly the same components, fire it again (in the same rifle, of course) and it could generate high enough pressure to tear the case head apart?

If so, this is an entirely new one on me, and I�d certainly like to know more about it. In close on forty years of reloading, and reading more books and articles on the subject that I can count, I have never heard of such a thing.

I hope that what I have stated and asked you does not sound confrontational. It is not intended to be, I�m simply after facts. Obsequious �weasel wording� has never been my style of writing.

wingnut:

Asking me if I am sure the bolt was fully closed is a bit like asking me if I am sure that I put my foot on the clutch when I changed gear at a certain bend in a road I drove along last week. I feel sure I would have done it automatically, but a positive recollection � no.

What I can say for sure is that the bolt handle was as far down as it would go AFTER the disaster occurred. It would be, though. Even if it was slightly raised at the time I pulled the trigger, the nose of the cocking cam striking the side of the notch in the bolt would have spun the bolt fully closed before the firing pin hit the primer. There was definitely no lube, moly or any other gunk on the case neck before firing.

Red

Redrover,I have no where near the expertice of some of these posters,but I have a P-17 that had headspace questions.Mine was a Canadian army one,they marked the bolts and it mismatched.After each firing I measured the case,they will fire when the bolt is part way down and the case will be longer.So Wingnut's question on P-17s about closing the bolt is not that out of place.With a properly cut chamber,the difference is less than a lot of factory rifles.I am following this post with great interest!

AJ300Mag, Hunting accuracy is kind of a subjective thing. Depends on the quarry, territory where the rifle is to be used and the projectiles most suited to the task. Shooting the NRA and military high-power circuit cured me of a lot of rainbow chasing and prima-donna nursemaiding. The rifle is, after all a tool. That tool ought to be so dependable and familiar to you that you can use it from sub zero cold to desert triple digit heat and with a variety of bullet weights. It should also feed flawlessly and be worked smoothly with no hitches. If this means it will never do a 5 shot group from a dirtied barrel (at least 3 fired through it before shoot for group) ... that is much better than minute of angle I can live with it because I will know its limitations and simply not chance a possibly poorly located shot. If I can't keep my end of the deal for some physical reason, I simply don't go that day. I've been told that I'm far less hunter than sniper and I suppose that this is true. You say you are a toolmaker. Mayhap you have been where there was a 10 EE for some no nonsense turning, or a big old Grand Rapids made Katty-corner South of you, a Cincy or a Milwaukee #2 for some dependable no shims mill work. If so you must then know where I'm coming from.

If you know how to seperate the wheat from the chaff, there are some few Bench-rest regimens that you can employ in a hunting rifle. Keep in mind that that fraternities developments got their start with hunting rifles. Surgeons developed from the town barber- right Dr.Todd?. I suspect I'd just as soon employ todays barber for a hair-cut. But not for brain surgery. Golf and Hockey.

It is possible you have made tools for working brass close to Ctg. brass, or other copper alloys. Be it that you have you will know that forming and drawing tools must conform to the nature of the alloy being worked. When Remington set out to start a whole new approach to firearms construction Post WW II, Momma Du-Pont
owned a 22% slice of the General,too, and Rem. got the services of Production experts with wide ranging experience in the metal working fields. From observations of the changes in barrel interiors someone did their homework on throats. There is an ideal leade angle for each type of jacket metal One for steel, another for the old Cupro-Nickel, another for Pure copper, and different again for Bronze and yet again for the more or less standard "Luballoy" type jacket metal.
In the 6m/m, Remington designed for what they wished to accomplish. A cylindrical section .118 long culminating in a short ramp from the cylinder to the top of the lands, and that, ideal, for the least ammount of effort required to deform the bullet while grooving the bullet to fit the lands yet not throw it off for the upcoming need for centrifugal balance was a goal that the designers reached. I suggested a test for RedR. If the neck tension was about normal he should have learned something about bullet entry into lands. In a Weatherby old style 3/4" long cylinder type freebore the projectile has a far greater velocity than the same bullet can achieve in a mere.118" travel. For different reasons in both instances the bullet will tend to orient itself to the long axis of the barrel bore. In the free bored throat the much greater velocity of the projectile can allow the bullet to deform to the rifling lands in an off center manner though axially in alignment. This does things to the core and adds to the everpresent centrifugel imbalance of the bullet in flight. If you have a 1:12 twist barrel and at some point past the muzzle the velocity is 3000 FPS that would mean the bullet has an identical RPM, doesn't it? You can't expect to turn a piece of stock at that RPM and maintain concentricity and hold size consistenly in a light skim cut can you?. IMHO ain't no way you can employ B-R techniques with a free-bore that can be very meaningful. Things you might do. Homework assignment. Clean and weigh the spent primer brass parts, anvil and cup. Paired parts at a time. Reord each weigh in. There should be so little weight variation that you cannot detect it. Next weigh live primers from the same lot and preferably from same container, one at a time. Segregate according to weight differential. Keep going until you have enough for say 20 rounds of firing. Fire 5 that are the left overs from your sorting so that you have,preferably 2 of the lightest,2 of the heaviest and one in the middle for your first string., Then 5, light, 5 midway and lastly 5 of the heaviest. The other components should be what you have thought to be an accurate loading for your rifle. If you have a powder scale that is not accurate enough to measure the weight difference between a postage stamp and then again the same stamp with a 1/4" long standard soft pencil mark on it, you are not playing the bench rest game. That usually means you have some sort of damper, oil or magnetic, or perhaps dirty balance knife and vee's. These should be cleaned with acetone before start anyhow. If you learn something from this, you will throw away the razor blade for cutting a cylinder of powder for that last .001 of a grain for each load. Next stunt. If you cannot find enough variation in bullets of the same weight ,remove enough lead that you have a spread of 5 grains. same drill as with primers. All shooting ought to be at 200 yards if you can do so.
Much better than the paper punching if you are concerned that you might hunch a few out of the group and which would not need a 200 yard range is to employ a Chronograph capable of measuring to plus or minus 2.5 FPS in the 3000FPS bracket. What you are looking for is the least variation in shot to shot velocity. That tool is a real time saver because loads of least shot to shot variation are generally the most accurate loads you can prepare. ( AND THE SAFEST) the closer you get to the max the more erratic the propellant burn and it gets exponential. If there is a more accurate Chrono than plus/ minus 2.5 it would be even better.

The best (least shot to shot variation) I ever got was total spread of 7 FPS on the Cascade Berkley Chrono at there range- in 10 shots. This machine measured to the last foot. It was the first use I put a 284 reamer to. A left handed shooter asked the powder capacity. When I told him about 30-06 he made a quick trip home and I punched his .308 Mod 88 Win .lever gun to a 30/284. I had 3 boxes of cases secured by unscrupulous means from the Win Ammo plant 6 months before the .284 hit the market in the M 100
Owner had to shoot it as a single shot for lack of magazine. The Cacade Chemist asked how accurate the load was and I told him I didn't know, but I was sure to be close inasmuch as I knew how hard the brass was at the head and simply measured for a uniform .0015" expansion over the head near extraction cannelure. Chemist thought that was cool. Jack O'Connor lived on top of the bluff nearly overlooking the plant, so we went to see Jack. He asked the same question. Told us he would surely like a target when we got a chance to shoot at one. All the rifle had was that fold up Lyman leaf, To me, what was the point? 15 miles out of Lewiston the Driver I rode down with spotted a burned stump, squealed to a stop, grabbed a piece of cardboard and charcoaled an aiming cross, and proceeded to back his jeep for 100 yards, found a suitable rest and dumped the remaining 7 rounds in a group you could cover with a 50 cent piece. I was suitably non-plussed because you gotta know when to be smug. We turned around and headed back to Jack's place. He was surprised to see us so soon and seeing the " target" gave away his thoughts because he couldn't erase the big grin soon enough when he looked at us and remarked, " Had I known you 2 impoverished A'holes needed a real target I could have afforded to give you one!"

Red, Well, you have the same problem at least 50 others have had wrapping your mind around what I outlined in my previous post to you. I cannot fault you because I have had the same problem with differential calculus. The burning of propellant in a sealed vessel capable of increasing in volume at one rate while the volume is increasing in another rate, neither rate of the same scale of measurement is what happened to you ,but set up in calculus form you would need at least 5 equations affected by each other but operating by different rules, then using methods empirically derived to mitigate the excesses in a physical sense could add even more equations to the mix. This probably comes closer to all of the variables encountered in building a thermo-nuclear device striving to get more bang for the buck. At no time did I ask you about the usual suspect things already brought up. You told me all that was important for me to form a very probable reason for the accident. You are still upset about my finding fault about your concern with diameter differences and I was adressing Volumetric differences. The dimensions I gave are from CIP which is translated up from SAAMI in this instance, although SAAMI prints now come in Imperial and Metric units. Where the case dimensions are given it was from measuring factory ammo by Remington. As before. they did what they did for a reason. What is the difference between the PPC capacity and the 6m/m capacity? Shouldn't there be an additional clue in that? You will need to go over the bit on volumetric and the Winchester solution for the .300 Win mag, and perhaps even draw a scaled print at about 5X to help. I know that it defies the imagination if you have been led to believe that the reason for the factory ctg dimensions to be off from max ctg print size is bedcause they can't seem to hold dimensions. I did explain why, but you are still struggling with dimensions to the power of one and I am talking Cubed as in Volume. I did not question the ability of your gunsmith either. He knows a good reamer when he sees one , perhaps you can get him to interpret a print out of my postings on this. I didn't bring up the 7 m/m Sharpe and Hart, but this is a method to get around propellant characteristics similar to Winch method with Win mag The reamers for that were licenced. Norma Ammo looked like it was made for a totally different chamber if you compared fired case with factory new. This drove Die makers and Reamer makers nuts. If you followed the S&H formulae you could almost get their claimed velocities and still have a one piece rifle and your head still on your shoulders.

the worst tyro of 'em all here, but i think i caught something others haven't. your 'smith told he remembered the reamer as having a .277 neck. have you actually measured it? did the 'smith ever actually measure it? it is conceivable that it might measure somewhat larger than "remembered," therefore giving you much less neck clearance than you thought you had. (or did somebody else catch this and i missed it in those long, beautifully and richly composed missives? what an education.

By waiting quite a while before I jumped in I was able to see what everyone else had to say first! Now I can throw in my opinion and maybe avoid sounding stupid. This is sometimes a tall order.
I don't think the neck diameter is in anyway responsible for the failure. I can't be quite so certain regarding pressure spikes or sympathetic pressure waves etc. I can't comment on the depth of the extractor cut or the exposed cartridge case because I don't have the rifle to examine.
The angled locking lug seats on the Enfields makes for an easy opening bolt so this makes bolt lift less reliable as a means of judging pressure. That the failed case was easily removed does hint that pressure was not unreasonable. The low bullet strike could indicate that velocity was low due to the "dumping" of pressure via the failed head or it could be indicative of shorter barrel time as a result of a dfifferent powder inadvertently loaded. I suspect the former.
In the final analysis this really sounds like a pressure spike sort of failure as described by Mr Burgess. Why this would have happened I can't say and venture to say no one else can either. The load of 4350 is a perfectly normal one. 4350 is generally a stable performing and quite forgiving powder. Pressure usually seems to build predictably. An undetectable hangfire would be one explanation. The bullet is moved into the rifling by the primer then stops. Pressure from the now ignited powder charge spikes before the bullet is able to start moving again. Ouch. The root cause? Who knows? Weak or contaminated primer. Blocked flash hole. Contaminated powder.
As far as neck dimensions are concerned, I think your dimensions are just fine. Not long ago I was out at the range with a man who was testing some new rifles. These rifles both featured tight necks which required neck turning. He was shooting molycoated bullets. I noticed he was having a heck of a time closing the bolt on the one rifle which was a 6.5x55 with a .290 neck. Once he got the bolt closed, he was able to fire the cartridge and everything seemed OK. I measured one cartridge he was unable to chamber and it measured .291 over the bullet so it was an interference fit in the chamber. Even those he was able to get the bolt closed on were .0005 over sized. I suspect the moly coating helped to ease things a bit. The load he was using was the same as what I used in my rifle and it is a fairly snappy load using 4831SC. So in this case the tight neck appeared to not be an automatic recipe for disaster as many would have us believe it to be.
I have no reason to doubt Mr Burgess' description of the factories' use of the undersized brass cartridge to "cushion" pressure spikes. It is an entirely believable explanation. There is some question as to whether or not it worked out for Winchester since the 300 magnum produces relatively anemic velocities for such a large case when factory loads are fired in factory chambers. Also, the chambers cut with parallel throats and of reasonable dimensions seem to be quite capable of approaching Weatherby performance without excessive pressures.
The failure in this case is similar to failures I have seen upon occasion with factory loads in factory chambers the cause of which was also unknown. They seemed at first to be simply defective brass but the actual problem was a mystery (at least to me)and may have also been a result of an unusual spike in pressure. Happily, such failures are rare. Regards, Bill.

I had a similar pressure situation in my 243 AI, using 41.8 Gr. of IMR-4350 and WLR primer. My conclusion was that I needed to turn down the necks of the brass to a smaller diamter, but I'm not sure that was the solution. Mine was in a Mauser which held together fine with no damage. I am reading these analyses with great interest.

downwindtracker2:

When you say that your M-17 has �headspace questions� I presume you mean that it is too long. (because if it was significantly too short, you would probably not even be able to chamber a factory cartridge) This WILL cause fired cases to come out longer, regardless of whether the bolt is fully closed or not � I tend to think that this is a quite separate issue.

With the original two-stage military trigger fitted, an M-17 (or a P-14) will not fire at all with the bolt open more than a few degrees, because the stud on the front of the sear cannot enter the narrow clearance slot milled into the underside of the bolt. The sear simply cannot be pulled down far enough to release the striker/ firing pin assembly. (unless, of course, somebody has made some serious alterations to the firing system)

My Enfield has a single stage over-ride type trigger in it, so it does not have this additional safety feature. I have been through arguments several times in the past about the effect of pulling the trigger with the bolt not fully closed. To satisfy my own curiosity, I experimented with some primed but empty cases. I chambered them, and tried pulling the trigger with the bolt handle raised by varying amounts.

The results were about what I expected. If the bolt was raised only a few degrees from fully closed, the primers did fire, and the bolt simultaneously spun down to fully closed. If the bolt was raised further amounts, the primer indentations were very weak, or non-existent, and again, the bolt spun closed. Most of the mainspring energy was obviously getting expended through the cocking cam nose hitting the side of the cocking notch in the bolt and spinning it closed.

I did not mean to imply in any way that wingnut�s question was out of line, and I apologise to him if I gave this impression.

Mr Burgess:

> � you have the same problem at least 50 others have had wrapping your mind around what I outlined in my previous post to you.

Only 50? Well, maybe. :-)

> You are still upset about my finding fault about your concern with diameter differences and I was addressing Volumetric differences.

No, the only thing really upsetting me is the damage to my highly prized rifle.

In my last posting, I attempted to ask you what I believe are two largely separate questions relating to your statements. You implied that one of the probable causes of this �blow up� was a tight neck � a �very tight� neck, in your words. Well, in your book, what case neck to chamber neck clearance - in inches or millimetres � constitutes a �very tight neck� situation? Surely this must be a linear measurement, not a volumetric one? Either the case neck does have enough room to expand radially (and easily release its grip on the bullet) or it does not. How much clearance do you think is necessary to permit this?

I freely admit that I am STILL trying to draw some clear conclusions from what you say about volumetric differences, pressure waves etc. etc. If that brands me as a dunce in some peoples� estimation, so be it. However, I must say that I am seriously concerned about some of the implications. To repeat my earlier question:

�Are you saying that one could fire a new or full length sized case with a certain load which generates high, but entirely acceptable pressure, then neck size the same case, reload it with exactly the same components, fire it again (in the same rifle, of course) and it could generate high enough pressure to tear the case head apart?�

Yes? No?

Please try not to be offended by my direct language � I�ve already told you that �weasel wording� is not my forte. I�d be a total failure in the Diplomatic Corps.

I can only say that if the answer to the above question is �Yes� or even a slightly qualified �Yes� then it constitutes a revelation of epic proportions. I must have fired tens of thousands of reloads using neck sized cases over the last forty years, and I know other shooters who have fired a great many more. It would make me wonder how any of us could have any of our centre fire rifles still intact.

Mr Leeper:

Thank you for your thoughts on the matter. I appreciate you taking the time to sift through this (now) very long thread, and make some pertinent comments. I take some reassurance from your opinion that there was adequate neck clearance for safety. I thought so, too � quite obviously, or I would have screwed the cutter of my neck turner in a bit further.

I agree that the angled locking lugs are a complicating factor. According to Otteson, they give a leverage ratio of about 100:1 in the final part of bolt closure, so I had to be very careful when setting up my F/L die to reform those 7X57 cases. To begin with, there was a lot of careful testing of how the cases chambered (with the firing assembly removed from the bolt) and taking the sizing die down in the press by a tiny fraction of a turn at a time until there was just the faintest trace of �feel� on the last few degrees of bolt closure. As far as extraction is concerned, if the bolt can be opened just with one finger and thumb then the cases cannot be sticking much, even if there is little or no lug-drag.

The thought of firing cartridges with �negative neck clearance� as you friend did gives me the creeps. (moly coated bullets or not) It�s interesting that there were no visible signs of excessive pressure, but it is still not something that I have any inclination to experiment with!

A VERY slightly delayed hang-fire is a possibility that I hadn�t thought of. As you say, though, it would be a difficult thing to prove. As far as the possibility of defective components are concerned, I can only say that primers from the same lot, and powder out of the same can, had always worked normally prior to my firing that fateful shot.

Maybe I will never know for sure what the cause of this blow-up really was. The worst of it is that I cannot PROVE beyond any possible doubt that I did not load the wrong powder into that one case. I can only say � quite truthfully � that my regular loading methodology SHOULD have prevented such an occurrence. Would you care to hazard a guess at what a load of 42grs of Varget instead of H4350 would do? The reason I ask is that Varget was the only other powder I had been using anywhere near the date that I loaded the ill-fated cartridge and its nine �brothers�. I am sure it would be an over-load, even with moly coated bullets, but to what degree � ? (if you don�t feel like publicly stating such a guess, I quite understand)

Do you think it would be worth getting a hardness test done on a portion of case wall taken from immediately in front of the case head? The head itself is so stretched and mangled that I�m sure the hardness of this will have been affected, but the undamaged case wall above should � I think � be of similar hardness to the original head metal. The problem I have with attributing the blow up to a soft case is that if this WAS the situation, I would have expected the case to show some obvious signs of failure on the first firing.

Is Earle Stanley Gardener still writing detective stories? Or Edgar Rice Bubbles? How about a new title � �The Case of the Blown Case�

Red

In defence of Todd Bartell, he had a very bad blow up himself a while back. Completely understandable he has a thing for that rifle. Damn near lost his eye.

This has been a very interesting thread, and I'll offer a guess as food for thought. It may have been simply a bad piece of brass, that held together for a while, then finally gave way, probably going all the way back to the sheet the brass was formed from. An impuritity inclusion, cold joint, etc. If posssible, a microscopic exam of the case -might- show something. Alas, along with other great mystries of life, you may never know...

Quote
"My Enfield has a single stage over-ride type trigger in it, so it does not have this additional safety feature. I have been through arguments several times in the past about the effect of pulling the trigger with the bolt not fully closed. To satisfy my own curiosity, I experimented with some primed but empty cases. I chambered them, and tried pulling the trigger with the bolt handle raised by varying amounts.

The results were about what I expected. If the bolt was raised only a few degrees from fully closed, the primers did fire, and the bolt simultaneously spun down to fully closed. If the bolt was raised further amounts, the primer indentations were very weak, or non-existent, and again, the bolt spun closed. Most of the mainspring energy was obviously getting expended through the cocking cam nose hitting the side of the cocking notch in the bolt and spinning it closed.

I did not mean to imply in any way that wingnut�s question was out of line, and I apologise to him if I gave this impression."

No need for apology, no offense taken, as obviously none intended.

I asked only because I knew of the possibility of an out of battery shot with some Enfields. There would be an excess headspace problem , AT THE INSTANT OF FIRING, that would not be detectable after the fact, due to the rotation of the bolt by the cocking cam.

My P-17 is a 308Norma,now,because of those " headspace questions" Headspace came up frequently on a M1917 forum,often enough that I wondered if it was part of the rifles.My cases ended up as much as 11 thou long,13 if the bolt handle was not tight down.I found and tested that at the range .Removeal of wood under bolt handle is a common repair for excess headspace.On mine I think the trigger is original,but with a screw on the back of it,so it's a single stage,and has the original cocking piece.(long drop) The firing pin will drop,if lugs just catch.I just dry-tested it. But at worst you are only looking at a few,2 or 3,thou. BTW On your rebarreled rifle,how is the headspace? The design leaves the case head dangling.

[ 05-15-2003, 05:03: Message edited by: downwindtracker2 ]

Pedestal:

Yes, I guess your suggestion of a metallurgical flaw in the cartridge brass, not simply the metal being too soft, is a distinct possibility. The split in the brass across the middle of the primer pocket, where things parted company, is a fairly clean break, almost a dead straight line, which may be significant.

Hopefully, I will have some close-up photos of the damaged case soon, which I will post here, and hope that people such as Mr Belk can deduce something from them. I won�t speculate any further until we have heard some expert opinions on what the photos suggest.

downwindtracker2:

It sounds to me as though your M-17 trigger has undergone more alterations than just having a first pull take-up screw added to it. What shape is the top of the stud on top of the trigger piece that the weight spring fits over? In its unaltered form, it is beveled on both sides, like the tip of a crudely fashioned, round shank screwdriver. When the trigger is pulled, the tip of it rises up through the hole in the bottom of the receiver, above the spring, and enters the small slot milled in the bolt body. Has the stud on yours been cut shorter, to de-activate it?

I have just been testing this feature on an un-altered P-14 action and trigger, and there is no way the thing will let the firing pin drop if the bolt handle is raised very much. The top of the stud hits the bolt body instead of entering the slot, and this prevents the sear moving down enough to release the striker. (as the designer(s) obviously intended)

The tests I mentioned doing with the bolt of my M-17 a fair way open were primarily to check if it could actually fire a cartridge with very little lug engagement, which would be dangerous in the extreme if it could occur. The firing pin would drop if the trigger was pulled when bolt was down any more than about 10 to 15 degrees (guessed � I didn�t actually measure it) but the primer would only go off if was down within a few degrees of fully closed.

I have been amusing myself pondering over the exact sequence of events which might take place in the latter situation using a fully loaded cartridge. Sort of thinking out loud, expanding on the point �wingnut� makes above:

If the trigger was pulled with the bolt almost completely closed, but not quite, the tip of the firing pin MIGHT contact the primer at about the same instant as the nose of the cocking cam on the striker contacted the edge of the cocking cam notch in the bolt.

If this did happen, and the firing pin hit with enough force to set off the primer, what would happen first? Would the impact of the cocking cam instantly spin the bolt the rest of the way closed? Or would the primer going off, and the powder charge starting to ignite, create enough back-thrust quickly enough to push the bolt lugs back into contact with their abutments before the bolt could turn that last few degrees? (and hold the bolt in this position by friction until after the bullet left the barrel and the pressure subsided)

Your experience seems to indicate the latter, verifying wingnut�s statement. Of course case lengthening due to this effect can only occur with Enfields, or other rifles with inclined locking lug faces. With the more usual square-cut lug faces, the bolt would already be fully forward by the time it was almost completely closed. But there is not even the remotest possibility of an Enfield bolt unlocking under back-thrust because it is not fully closed - the incline on the lug faces is nowhere near steep enough to cause this. So it is not really a safety issue, except for the additional few of thou of case lengthening. This could become a safety issue for an unwary reloader, but that�s another story.

You asked about the headspace in my blown up 6mm. The gunsmith says it was dead-on when he chambered and fitted the new barrel, and he�s such a perfectionist that I am quite prepared to believe this. The tests he did with a set of headspace gauges after the disaster show that it is now almost 0.003� too long, so it looks like something has stretched.

Red

BTW � You might be able to hunt LONGER with the wind at your back, but I have always found that I hunt much SUCCESSFULLY with it in my face!

spiral cam of bolt. Supposed to be .100" in one complete 360 rotation, 1/10 rotation= 36 degrees, and .010 difference in headspace. With that much variation in factory unfired loads ,at times, and your rifle with no headspace gap as you load, Bolt not closing would A, be rather noticable and,
B, at 36 degrees .010 .
Flawed case with split unlikely to wait for a 2nd firing to show up. More likely; Represents the unsupported part of the case. Bolt rim support,stops the movement in one direction and only way to go when you feel the move is out the unsupported part of the bolt face. Spelter goes down the left lug raceway from this source.

Systeme98,

What do you mean 360 degrees? Doesn't most bolts rotate 90 or 60 degrees?

I think I've read all the posts,but maybe something fell or crawled in your empty primed case, or .257 bullet in wrong place. you'd like to think......

Old Action:

> maybe something fell or crawled in your empty primed case,

Not totally impossible, I suppose, but 42grs of powder gets a 6mm Rem case fairly well filled up just on its own. There wouldn't be room for much else, and if it was something inert ...??

> or .257 bullet in wrong place. you'd like to think......

Sorry, but no cigar for this one. I don't own any 25 calibre rifles, and I don't have any bullets this diameter. But even if one of this size had somewhow got into the box at the factory, then:

A: I imagine it would be difficult to seat a bullet that was 0.013" over-size without being able to tell just by the feel of the press arm that something was very seriously wrong, though I've never actually tried to do such a thing.

B: Even if I HAD managed to seat such a bullet, it would have been nigh-on impossible to chamber the cartridge, because with the correct diameter bullets (0.0243") seated, there was 0.0045" total neck clearance. The force required to close the bolt would have been colossal (if it could even be done at all) and I most definitely would have noticed this.