My interest is piqued with this gas-check stuff, I haven't seen much discussion on this before beyond just annealing. Wouldn't it be nice to actually see what's going on inside the barrel at a million frames per second?

Gear

I've got three gas checks I'm going to test out on that 30 caliber bullet. I have a very consistent load for that AR 10 and you've seen a typical target from it. One is a Hornady, another a soft aluminum, and the third is a hard aluminum.

I've gotten the soft aluminum to fail with an extremely hot load in a Finn 39. I repeated the test with a Hornady and it did a little better.

There's one other material I've made checks from that most all of you would be sick to think of using. That's mild steel.

quote:

Originally posted by SmokinJ:
I've got three gas checks I'm going to test out on that 30 caliber bullet. I have a very consistent load for that AR 10 and you've seen a typical target from it. One is a Hornady, another a soft aluminum, and the third is a hard aluminum.

I've gotten the soft aluminum to fail with an extremely hot load in a Finn 39. I repeated the test with a Hornady and it did a little better.

There's one other material I've made checks from that most all of you would be sick to think of using. That's mild steel.

What's wrong with mild steel? Steel-jacketed bullets work fine, and in the case of a steel gas check, there's lube in the barrel anyway so I don't see how it would be much worse than camshaft lobes on flat tappets.

Gear

quote:

Originally posted by Geargnasher:

quote:

Originally posted by SmokinJ:
I've got three gas checks I'm going to test out on that 30 caliber bullet. I have a very consistent load for that AR 10 and you've seen a typical target from it. One is a Hornady, another a soft aluminum, and the third is a hard aluminum.

I've gotten the soft aluminum to fail with an extremely hot load in a Finn 39. I repeated the test with a Hornady and it did a little better.

There's one other material I've made checks from that most all of you would be sick to think of using. That's mild steel.

What's wrong with mild steel? Steel-jacketed bullets work fine, and in the case of a steel gas check, there's lube in the barrel anyway so I don't see how it would be much worse than camshaft lobes on flat tappets.

Gear

Gear,

With all the hoopla over aluminum checks wearing a bore that those that think that would really think a person was crazy to use steel checks. Like you mentioned the military has used steel jacketed bullets for years with about equal wear to the barrel as using the copper alloy jacketed bullets.

The only thing that might even be a slight concern with aluminum checks is using aluminum which has been anodized, with the anodized surface to the outside. Such a finish is EXTREMELY hard, although very thin. Even then, just because it's hard, doesn't mean it's necessarily abrasive to steel barrels, especially with lubricated cast bullets. It takes billions of cycles for chrome-moly piston rings to cause significant wear soft cast-iron cylinder walls.

Gear

quote:

Originally posted by Geargnasher:
The only thing that might even be a slight concern with aluminum checks is using aluminum which has been anodized, with the anodized surface to the outside. Such a finish is EXTREMELY hard, although very thin. Even then, just because it's hard, doesn't mean it's necessarily abrasive to steel barrels, especially with lubricated cast bullets. It takes billions of cycles for chrome-moly piston rings to cause significant wear soft cast-iron cylinder walls.

Gear

Don't forget that aluminum check goes through the sizer die before it's shot. Don't you agree that would "tone" it down?

Von and Gear,

I used a RCBS type neck expander and flare on those 7.62 cases. In fact I use them on all my calibers. Wouldn't do it any other way.

I stopped flaring the necks on my cases after I got a VLD chamfering tool and gave the inside of the neck a vld chamfer almost to the outer edge. I also only have 1-1 1/2 thou neck tension so there is no seating deformation and they can still be loaded from the magazine with no worry about missalignment caused by the feed ramp.

quote:

Originally posted by Von Gruff:
I stopped flaring the necks on my cases after I got a VLD chamfering tool and gave the inside of the neck a vld chamfer almost to the outer edge. I also only have 1-1 1/2 thou neck tension so there is no seating deformation and they can still be loaded from the magazine with no worry about missalignment caused by the feed ramp.

Yup that will work. I also use that same neck tension. There have been some heated debates over the RCBS and the Lyman step expanders.

Von,

You ever play around with shotshell buffer in your cast loads? I've done it quite a bit.

quote:

Originally posted by SmokinJ:
Von,

You ever play around with shotshell buffer in your cast loads? I've done it quite a bit.

Not shot shell buffer but I did use the usual dacron and some wool balls but found that they were only marginaly useful when I got to the higher load levels with my HV loading as the powder was in the 80% load density with the H4350. My lighter loads are with powders that are not position sensative as in Red and Blue Dot.

quote:

Originally posted by Von Gruff:

quote:

Originally posted by SmokinJ:
Von,

You ever play around with shotshell buffer in your cast loads? I've done it quite a bit.

Not shot shell buffer but I did use the usual dacron and some wool balls but found that they were only marginaly useful when I got to the higher load levels with my HV loading as the powder was in the 80% load density with the H4350. My lighter loads are with powders that are not position sensative as in Red and Blue Dot.

Buffer can make a small amount of powder act like a much larger charge plus it does a whole lot more beneficial things. It's a whole new area of cast loading if you haven't been into it before.

You're right about the fiber fillers.

Well I tested my gas checks. Remember was going to test Hornady, my soft aluminum, and my hard aluminum. The Hornady and the soft aluminum were a virtual tie. The hard aluminum checks on the other hand were terrible. Not conclusive until I shoot them all a few more times.

Joe, a little birdie told me one time about designing the boolit's GC shank such that the check practically touches the base band all the way around. We know square muzzle crowns are critical to accruracy, and square boolit bases almost as critical, so I can't help but think that factors like gas check strength and how it's supported by the case neck, throat, and the bullet itself all contribute very much to accuracy.

Gear

Joe

That design is almost a duplicate of the excellent LBT bullet that Bass Ackward uses for HV/RPM success. I also used it for very, very good success. It is almost exactly as I described a cast bullet should be to push the RPM threshold up in a faster twist barrel. Your Von Gruff's 7mm bullet has all of the same design features which is one of the major reasons he is as successfull as he is with his 7mm.

That basic design that 45 2.1 uses now for several bullets (absolutely no criticism there, actually a bit of praise) is probably one of the best. It also is a design that has been used quite successfully by several CBA shooters who shoot at HV. It is also why you are succesfull at HV/RPM. I've hopes for the similar 22 NATO bullet 45 2.1 designed.

Just a couple simple questions here so don't get all in an uproar; do you think you can shoot as successfully at HV/RPM with regular cast bullets such as a 311291 (even a very good fittingone)in your .308W AR ir the 266469 or 266473 in your 6.5s instead of the custon Kurtz design?

Larry Gibson

I don't normally come to this forum, but a regular contributor to it brought this discussion to my attention, indirectly.


I don't plan to argue about any powder mixes, rpm thresholds, any of that stuff.

Just want to make some observations about things related to cast bullet accuracy, which may or may not apply to specific instances any of you guys are experiencing.


1. The most important thing in relation to CB accuracy which I have seen in cast bullet shooting competition seems to be matching the bullet diameter & shape to the THROAT of the chamber.

I had a CB BR rifle built for me by John Ardito, (many time CBA Grand National BR Champion) when I first started CB benchrest competition in 1993. I could not get it to group under 1/2" for 5 shots at 100 yards and was disappointed. At that time group aggregates under 1/2" would win many matches, but agregates over 1/2" usually put you in about 8th or lower place in a field of 30 shooters.

So I had the late Larry Jennings (former holder of many, many CBA national records) look at it for me. He told me the throat was, for some unknown reason, .3145" diameter, but that it would shoot well if I quit using .3115" sized bullets and increased their sizing to .3145" to fit the throat. I tried that using a bump die John made for me. The throat-sized Lyman 314299 bullets immediately started grouping in 0.400"<0.420" at 100 yards. The barrel groove diameter, incidentally, was .3085". The cartridge was .30 BR and the velocity was about 2,200 fps with 178 gr. bullets.


2. Bullet design is important. For seven years I shot at least 200 rounds per week under competition conditions, and and many more under test conditions trying every kind of .30 bullet mould, alloy, and bullet shapes I could lay my hands on.

The late Don Eagan's brass moulds casting his MX4-30A bullets (198 grs.) and MX4-30ARD (212 gr) bullets outperformed every other bullet on the market which I tried during those years by a wide margin in my rifles.


3. Lube is also important. Mel Harris (3 or more times Grand National Champion), David Lee (holder over the years of at least 10-to-15 National Records, Gary Long (holder of the first CB national record 5-shot group of 0.15" or smaller at 100 yards shot in a registered match) and I all shot together regularly in our small home town. Basically what we found worked for us was that using hard lubes with hard alloys at high velocities and soft lubes with soft alloys at lower velocities, gave us our best accuracy from our particular rifles, chambers, and throats. All of our gun chambers were intitially cut with combinations of my chamber and throating reamers. We all used Hart 1-in-11" twist barrels except for my second one. It was a Harris barrel with the same twist.

Dave Lee, for instance, who may have been technically the best shot of all of us, seldom won matches until Mel and I convinced him to go from soft lubes like Javelina to LBT Blue or even harder lubes for his linotype bullets when he shot at 1,950 TO 2,100 fps. Then he instantly started winning and setting national records quite regularly.

Eventually we all ended up shooting Eagan mould MX4-30 bullets made of pure lino, lubed with Thompson's Blue Angel, and propelled by Vihtavouri N-133, N-135, 2230-S, or H-4895, pretty much interchangeably. I also tried a mix of N-133 and N-135, and it worked just fine. I quit using it when I ran out of the 2 pounds I had accidentally mixed (but used-up rather than throwing it away).

Dave shot Eagan's 212 grain bullets (including lube and Hornady gas check) at about 2,000 fps most of the time, Mel shot the same bullet at about 2,050 fps, and I shot mine at 2,305 fps. I don't recall Gary Long's velocities with the same bullet, but it was at least 2,050 fps.


4. Interestingly enough, we all loaded our match ammo differently, so that aspect apparently is NOT critical to accuracy. Dave sized and loaded his "Match" cases between each relay as a general rule. Mel pre-loaded his ammo before the match much of the time and between relays other times. Gary ALWAYS pre-loaded his whole day's match ammo IIRC. I used only one case during a match, and NEVER sized my brass, ever, after first making it and fireforming it. I reloaded the one case chosen for any given day's matches between every round I fired. I owned neither a sizing nor seating die in .30BR; still don't. Just a decapper, recapper, and powder measure.



So, finally, to the subject of SmokinJ's thread.

From my limited experience. I'd say that cast bullet accuracy is dependent on doing a lot of things so they fit together as a consistent, reliable, high performance "SYSTEM".

I have no idea why bullet fit to throat is so important, but have a lot of conjectures, none of which matter until a test thesis is postulated and tested.

But, if was going to start trying to shoot heavy .223 bullets in fast twists, I would begin by investigating bullet shape and diameter vs. chamber throat shape and diameter and match them together the best I could. When I found something which works fairly well and consistently, I would start trying harder and harder lubes just to see what the range of useable lubes would be in my rifle with that bullet.

Lastly, I'd do just what we used to do with our BR rifles for the final tune. On match day we'd start with our "generic" powder charge, and tweak it up or down in steps of .08 grains at a time while shooting on the sighter target to see exactly what it liked best in the ambient conditions of the day. (.08 grains is one "click" on my Jones powder measure) And we'd write down both what the conditions were and what worked best for us as powder charges that day...all for future reference in deciding on loads.

A logical scientific explanation? No. But it worked for us. For several years one of us, Dave, Mel, Gary, or I, won just about every match we entered, including the nationals. And in the regionals we often swept the top four places overall.

A big-time PITA? Yup. But no one ever said accuracy was easy....just that finding it is fun.

AC,

Very interesting post. I didn't know you shot cast,but then again it doesn't surprise as know you you've done a lot of things.

You're so right about that throat fit, lube, and loading technique.

Thanks for sharing with us.

Von,

I went to that website you posted the link to. I really liked the look of that 7x57 you have there.

I have a 7mm-08 SAKO Mannilicher carbine that I've shot some cast from. For low velocity I shoot the Lyman 180 grain Loverin. It does exceptionally well till you try to press some velocity out of it. It won't do it. Another factory bullet mold I use is the LEE 135 grain 7mm. My SAKO loves it. I've gotten that bullet up to just under 2700 fps and it shoots a 3/4 inch group. It's a difficult rifle to shoot for me being so light weight, short barrel (18.5 inches) and a small scope which is a Burris Mini 3x9. It does well for all that in my opinion. Not all my good shooting bullets at HV are with custom molds and designs.

Alberta Canuck

Well documented post that backs up what most of us have beem saying for years; fit cast bullets to the throat, not groove diameter.

Larry Gibson

Thought I'd throw in one more comment. Which lube-sizer or make of sizer dies we used didn't seem to make a one whit of difference either.

Dave always used a Star luber-sizer, Mel used an RCBS, then later only a Saeco as far as I can recall, Gary ended up using a Star the most as years went by. I liked to experiment, so I used a Lyman 45, two Lyman 455s, two different Stars, a Lee, four different Saecos, and so on....I still have all of them, stored in plastic "Totes". (I liked to try different lubes with different bullets over the years. So I kept different sizers full of different lubes as I DID NOT enjoy the mess of changing from one lube to another in any given sizer.) The brand I like using the best is probably obvious, the Saeco.

Very early we all found out that the marked sizes on sizing dies, regardless of make, are seldom closer than +/- .001". Any given die marked ".311", for instance, could size bullets to anywhere from .310" to .312" and be within the manufacturer's acceptable tolerance specs.

So we'd buy dies marked at least .001" smaller diameter than we wanted our bullets. Then if they actually were too small, we'd lap them out to what we needed.

Von,

Do you make your own gas checks? If so what tool do you use. I'm wondering if my hard aluminum check didn't fair as well in my test because it's base wasn't formed as square corners as the softer aluminum and the Hornady check. What is your opinion on that?

Fitting the bullet to the rifle's throat is only the beginning.

The Bullet Joe was using with no joy in the 5.56 AR was designed to be a perfect match. It seems that in this case the system is especially finicky about powder ignition and burn rate, because only the blended powder brought the groups together according to Joe's tests.

Gear

quote:

Originally posted by SmokinJ:
Von,

Do you make your own gas checks? If so what tool do you use. I'm wondering if my hard aluminum check didn't fair as well in my test because it's base wasn't formed as square corners as the softer aluminum and the Hornady check. What is your opinion on that?

I have one of Charlies Freechex tools. Actually a second one because I wanted to work to my gc shank dia that didn't take to well to the standard size that Charlie made. The second tool has a seperate solid disc cutter and cup former nd a heavier duty die as I wanted to work with the .021 copper although I still did some lapping to get to where it made GC without drawing the sides of the cup down. I also tried using a push through sizer a 1/2 thou larger than desired finish size to pre seat the GC and ensure a square fit and flat base and then finish sized them in the lubrisizer. I also adapted an un-used die to take Wilson neck sizing bushes so I could size the nose on ,my bore rider so it was a 1/2 thou under bore dia till engagement so I could seat for optimum base seating to case neck. This was only for less than a 1/4 inch of the nose then it reverted to a 1/2 thou larger than bore dia.

quote:

Originally posted by Geargnasher:
Fitting the bullet to the rifle's throat is only the beginning.

The Bullet Joe was using with no joy in the 5.56 AR was designed to be a perfect match. It seems that in this case the system is especially finicky about powder ignition and burn rate, because only the blended powder brought the groups together according to Joe's tests.

Gear

Most certainly more going on in that 5.56 bore with a 7 twist. That bullet has a very small cross section area for the pressure to work on as opposed to the larger cross section area of say a 6.5 bullet or a 30 caliber. Bullet material is a part of the mystery, but even switching to a hard alloy doesn't solve it completely. I must have really spread out the soft push of a very slow powder to prevent what was happening to bullet loaded otherwise. Lot's going on...when the bullet is in the case, when it's in the throat, when it's in the bore, and when it leaves the muzzle.

This is the neck sizer adapted for an un-used lube dia for nose sizing. It is easy to try different sizes for different requirments. You can see in the pic where I have sized the nose just far enough to ensure engagment at chambered length to suit a neck-shoulder junction for the bullet base

quote:

Originally posted by Von Gruff:

quote:

Originally posted by SmokinJ:
Von,

Do you make your own gas checks? If so what tool do you use. I'm wondering if my hard aluminum check didn't fair as well in my test because it's base wasn't formed as square corners as the softer aluminum and the Hornady check. What is your opinion on that?

I have one of Charlies Freechex tools. Actually a second one because I wanted to work to my gc shank dia that didn't take to well to the standard size that Charlie made. The second tool has a seperate solid disc cutter and cup former nd a heavier duty die as I wanted to work with the .021 copper although I still did some lapping to get to where it made GC without drawing the sides of the cup down. I also tried using a push through sizer a 1/2 thou larger than desired finish size to pre seat the GC and ensure a square fit and flat base and then finish sized them in the lubrisizer. I also adapted an un-used die to take Wilson neck sizing bushes so I could size the nose on ,my bore rider so it was a 1/2 thou under bore dia till engagement so I could seat for optimum base seating to case neck. This was only for less than a 1/4 inch of the nose then it reverted to a 1/2 thou larger than bore dia.

I use to make my own freechex but they are just too painfully slow for the volume of shooting I do. I make a one stroke on finished gas check die like the one you see in the picture.

I dont necessarily volume shoot the way you guys volume shoot and an enjoyable afternoon in the sun or an evening in fromnt of the tv can get more than enough made to suit my needs. I have made something to make them on and save them in and it will take nearly a thousand before I have to empty them into my storage jars and for me that is a lot of shooting.

Amazing how some our components look the same...like the material strip. Sure beats paying the high price for factory checks.

Instead of using the hammer now I have found that my Sinclair arbour press works for the single layer checks that I make with the Frechex tool in 44 cal and I got a second forming stem that makes perfect checks from the same die for my 404 jeffery at least for the plinkers. Still use the Hornadies for the HV loads as I had a 1000 and it will .take a while to shoot my way through them

quote:

Originally posted by Von Gruff:
Instead of using the hammer now I have found that my Sinclair arbour press works for the single layer checks that I make with the Frechex tool in 44 cal and I got a second forming stem that makes perfect checks from the same die for my 404 jeffery at least for the plinkers. Still use the Hornadies for the HV loads as I had a 1000 and it will .take a while to shoot my way through them

When I used the freechex style I used my drill press to cut the discs.

Okay, let's get this back to the original topic and that is it's not the rpm of the bullet that is causing inaccuracy. Myself and others have proven that. Like I've said, and others in the field of ballistics, have said if a bullet is balanced over spinning it won't ruin the accuracy enough to make a difference. This is shown with jacketed bullets being shot in many fast twist rifles of various caliber, plus many of these rifles shoot the shorter lighter bullets (which definitely don't require such a fast twist) to very good accuracy that often exceeds the accuracy of the bullets that are suppose to do better in the faster twist.

So with my playing around with blending powder and drastically changing it's pressure event on the cast bullet has let the bullet go further up the velocity scale with accuracy. I know my alloy is at the limit, even below the limit in the 5.56 with a 7 twist. So it's alloy and how the pressure curve acts, plus their may be some negative things happening at muzzle exit. I also believe something changes or happens to the bullets surface while in the bore.

So brain storm. Let's hear what others have found...not think...as thinking something does this or that is what starts the arguing.

Joe

You are quite right, it is not the RPM that "causes" inaccuracy. It is the imbalances in the bullet. The increased RPM is what affects accuracy. The better ballance and stabilized the bulet is the higher the RPM it can be driven to and maintain accuracy.

Gearnasher from a post today on the CBF; "Now, for hunting with cast boolits, First the Mosin. It will take a lifetime to learn how to shoot gas checked boolits accurately at much above 1900 fps in that rifle, much less 2600."

Seems a bit of a reversal there for gear in this and the other thread here on AR. Seem he now agrees with me! Be that as it is joe, why do you suppose it is so difficult to shot GC'd bullets accurately above 1900 fps in the Mosin 7.62x54R?

Larry Gibson

quote:

Originally posted by Larry Gibson:
Joe

You are quite right, it is not the RPM that "cases" inaccuracy. It is the imbalances in the bullet. The increased RPM is what affects accuracy. The better ballance and stabilized the bulet is the higher the RPM it can be driven to and maintain accuracy.

Gearnasher from a post today on the CBF; "Now, for hunting with cast boolits, First the Mosin. It will take a lifetime to learn how to shoot gas checked boolits accurately at much above 1900 fps in that rifle, much less 2600."

Seems a bit of a reversal there for gear in this and the other thread here on AR. Seem he now agrees with me! Be that as it is joe, why do you suppose it is so difficult to shot GC'd bullets accurately above 1900 fps in the Mosin 7.62x54R?

Larry Gibson

First Gear isn't changing his opinions. Now to the Mosin. I don't find it hard to shoot the to higher velocity with accuracy above that 1900 fps. I'll tell you a good portion of what is for many. Bullet fit. Mosin's have chambers, throats, and bores all over the place. Take the very good Finn 39's. The have a god awful long throat in them to shoot that Rooskie heavy bulleted machine gun ammo. In addition they have fat neck dimensions in the chamber. I don't think you remember that 10 shot target I posted on CB with my FINN 39. Maybe if I told you that a bird pooped on that target you may remember. It was the Lyman 314299 over some 4350 and the muzzle velocity was slight over 2000 fps. I wouldn't call that, in my opinion, really high velocity but it's higher then the average cast bullet shooter shoots at. The group was 1/2 inch.

Now I'll tell you something you don't know I've done with my FINN 39. I made a blistering load of a booster with my 867 powder. My 314299 weighs around 210 grains. It chronographed a little over 2600 fps. So I went out to put it on paper and zero the scope which I had set for a totally different much lower velocity. I had a giant piece of paper out. Larry I couldn't for the damn of me get it on paper. Oh maybe a bullet or two. I thought something was wrong. Well there was. I went up at 15 feet and shot two rounds. Guess what? Both 100 percent keyholed. What I had done was exceeded the strength of my alloy drastically. I tried some check material changes and shot again at 15 feet. The harder check made "some" difference,but still showing bullet tilt. Amazing to all this is your could eat off the bore! Not a trace of leading..zero on the muzzle. Case mouths and necks clean as a whistle. Primers by the way had cratering around the firing pin indent. Checking the jacketed reloading manuals I was where I shouldn't have been with that rifle and load. What do you think about that?

By the way an increase of rpm you were speaking of only affects an unbalanced bullet. If the bullet is only slightly unbalanced it may not show up until high velocity/rpm rear their heads. Also to get higher velocity you need a higher pressure and it's quite possible the higher pressure deformed/damaged the bullet.

One of my "suspicions"(not provable facts) about why bullet fit to rifle throat is so important, has to do with gas-deformation and associated unbalancing of bullets.

I SUSPECT that some bullets which don't obturate to completely and uniformly restrict gas flow in the throat instantaneously on firing (or even before firing) are subject to gas bypassing the bullets and cutting some of them before they ever even get into the bore. The gas may also scatter or otherwise randomly redistribute lube pushed or yanked out of the bullet grooves by its passing.

Gas cutting and/or lube movement are not necessarily uniform, even if the cast bullets start out as 100% uniformly dimensioned inside and out, which they seldom do.

So one then may have a turning, accelerating, physically imperfectly-balanceable bullet which soon leaves the confining controls of the bore surfaces via the muzzle.

Why wouldn't it fly in an unbalanced manner when cruising unsupported through the air and its variable non-homogeneous resistance, and produce occasional if not frequent big-time and/or small fliers?

I dunno, of course. But I suspect that's just one of many culprits found in loads which don't shoot well, fast twist, or slow.

Sometimes I'm utterly amazed by just how well cast bullets do manage to fly.

Yup, that's another possibility AC. Mann was a firm believer in the bullet getting kicked the wrong way at exiting the muzzle. Or perhaps even damaged by the exiting gas. I believe he only experimented with plain flat base bullets. We have it better today with are different alloys and gas checks.

My peers and I have been stressing all along minimum case neck clearance so that bullet base doesn't have much an area to move too and the gas also doesn't have much room to get around the base.

quote:

Originally posted by Larry Gibson:
Joe

You are quite right, it is not the RPM that "cases" inaccuracy. It is the imbalances in the bullet. The increased RPM is what affects accuracy. The better ballance and stabilized the bulet is the higher the RPM it can be driven to and maintain accuracy.

Gearnasher from a post today on the CBF; "Now, for hunting with cast boolits, First the Mosin. It will take a lifetime to learn how to shoot gas checked boolits accurately at much above 1900 fps in that rifle, much less 2600."

Seems a bit of a reversal there for gear in this and the other thread here on AR. None whatsoever. You're taking a partial post out of context and twisting the meaning to misrepresent what I meant, and the reason behind my statement. This sort of deliberate word-twisting ranks right up there with theft, lying, and slander in my book and I'm sick of you doing this to me and others. Neither do I appreciate you responding to Joe by trying to start a personal fight again without adding a single, valid point or fact to the topic of conversation. Where I come from they call this being a TROLL. Seem he now agrees with me! Be that as it is Drop the God complex Larry, just because you make something up and present it as a statement of fact doesn't make it so. joe, why do you suppose it is so difficult to shot GC'd bullets accurately above 1900 fps in the Mosin 7.62x54R?

Larry Gibson

All right, for the rest of the story. A member at CB, who has never cast a bullet in his life, wants to make a hunting load in the 2600+ fps range for his military Mosin Nagant. He's read enough to know he "needs gas checks" or "paper patch" to achieve this, but what he hasn't the foggiest notion about bullet fit, loading cast, or anything. He's completely green. Telling him how to beat the balance monster won't do any good because he has no frame of reference yet, and I was presenting him a realistic picture of what he can expect to achieve with "standard" loading techniques, i.e. what the Lyman manual or others like it tells you. I also mentioned alloys and how cast bullets have a different range of ideal terminal performance than do copper-jacketed hunting bullets. I think I painted a realistic picture for him, which is what he needed.

So, WHY 1900 fps? For the reasons Joe stated, somebody who doesn't know what they're doing won't be able to achieve the things necessary to cast, load, and shoot a lead bullet out of a MN without having a mangled mess coming out of the muzzle. I never argued that mangled messes are usually terribly unbalanced and only shoot so-so at low velocities at best. Lower velocities don't exacerbate the effects that lack of throat support on the bullet, excess chamber neck clearance, poorly fitted, FL-sized brass, improper case neck expansion, poorly chosen components, and a myriad of other pitfalls have on cast bullet accuracy. You call it the "rpm threshold" because you attribute your findings to the rotational velocity of the bullet. I think that's a backward way of looking at it. The cause of the inaccuracy at higher velocities has to do with loading technique, not RPM. To say that you can "push the threshold upward" makes the threshold meaningless when one can take a bullet to 220K rpm with accuracy by correcting balance issues but your "threshold" maxes out (with typical loading methods) at 140K or so.

Everything has limits. Take a bolt-action .30-'06 10 twist, just about everyone that shoots has one. Load it with plain-based bullets, accuracy might be 1.5-2 moa and goes away at 14-1600 fps normally. Add a gas check, take it to 1900 fps with the same accuracy. Specialize the alloy and gain maybe another 150 fps. Correct the fit and some other things and shoot WD 50/50 alloy to 2400+ fps with even better accuracy, but it will peter out if you push it much faster(you don't know how to do this). Paper patch the same bullet, even with air-cooled 50/50 alloy, delete the gas check, and you can push it to the pressure limits of the cartridge with MOA or better accuracy. Each example has its own set of operating limits, and when you exceed them, the accuracy goes south. It ain't RPM that kills it, it's the inability at each limit point to continue to launch the bullet straight and balanced that kills accuracy. You may think it's the same thing saying "balance" or "RPM", and the two are connected, but only in the most abstract way. Balance isn't the only thing going on with the above examples that ruins accuracy above a certain velocity. You change twist rates around and can squeak more velocity with the same accuracy, but it isn't so much the RPM that's being sidestepped there, it's the LAND PRESSURE that's the bugaboo. Merely saying "It's the RPM that's the problem" is not only a poor description of the phenomena, it's a very incomplete one with too much variable range to have any real meaning. You have yet to realize fully what CAUSES the accuracy/velocity issue, and when you do you'll realize that attributing it strictly to rotational velocity of the bullet is no more conclusive than Richare Lee attributing it to alloy yield strength and peak pressure.

So, to be perfectly clear, the only thing we agree on is that there will be an accurate velocity limit to each particular gun/component combination.

JOE: I maintain that the principle cause (assuming everything else is done right) of the ultimate failure of a cast bullet to achieve accuracy beyond a certain velocity in any twist involves bearing surface limits and base squareness, particularly at muzzle exit. My reasoning is based upon the observed effects of paper jackets, copper jackets, and grease-groove bullets, particularly this last where I've recovered bullets that were shot at velocities beyond the "accurate limit" of the system and noted the engraves were obviously stressed and distorted on the drive side, and the bases were quite observably not square. This land distortion and square base effect was not observed on bullets fired accurately out of the same system at slightly lower velocity. I wish I had a good way to recover bullets, I might be able to actually say something conclusive about the relationship between twist rate, velocity, and this sort of bullet damage, but I've only recovered a few examples from two guns and two loads.

Gear

quote:

Originally posted by Alberta Canuck:
One of my "suspicions"(not provable facts) about why bullet fit to rifle throat is so important, has to do with gas-deformation and associated unbalancing of bullets. ]Deformation of the bullet in the throat during initial pressure rise and transition into the barrel is provable by observing recovered bullets. This is why chamber neck and throat fit are so important. You can indrectly observe the effects of throat fit simply by firing two series of bullets of the same weight and same load, one with minimal tolerance in every dimension, and one with some a large unsupported area at launch.


I SUSPECT that some bullets which don't obturate to completely and uniformly restrict gas flow in the throat instantaneously on firing (or even before firing) are subject to gas bypassing the bullets and cutting some of them before they ever even get into the bore. The gas may also scatter or otherwise randomly redistribute lube pushed or yanked out of the bullet grooves by its passing. I call this "Dynamic fit" and "lube blowby". Lube blowby leads to "running over the lube" further up the barrel, causing problems of its own in the instances of "wrong" lube formula, poor dynamic fit due to alloy strength and/or exessive clearances, or as I'm learning now, grease groove design.

Gas cutting and/or lube movement are not necessarily uniform, even if the cast bullets start out as 100% uniformly dimensioned inside and out, which they seldom do. One of the keys to accruracy is minimizing or at least uniforming the dynamics changes at launch.

So one then may have a turning, accelerating, physically imperfectly-balanceable bullet which soon leaves the confining controls of the bore surfaces via the muzzle.

Why wouldn't it fly in an unbalanced manner when cruising unsupported through the air and its variable non-homogeneous resistance, and produce occasional if not frequent big-time and/or small fliers? I believe that they do, based on results. I also believe this is what Larry Gibson defines as the RPM threshold, the point that the imbalance starts ruining groups. Thing is, inaccuracy is also caused by bullets leaving the muzzle on a tangent, even BALANCED bullets, because of the effects of barrel harmonics and bases not being square to the muzzle crown. The point that tangent muzzle exit and the effects of balance start to become evident is similar. It isn't just a balance thing.

I dunno, of course. But I suspect that's just one of many culprits found in loads which don't shoot well, fast twist, or slow. I agree on that, too.

Sometimes I'm utterly amazed by just how well cast bullets do manage to fly.

You and Joe beat me to it before my last post, but I see we're thinking along some similar lines.

Gear

quote:

Originally posted by Geargnasher:

quote:

Originally posted by Larry Gibson:
Joe

You are quite right, it is not the RPM that "cases" inaccuracy. It is the imbalances in the bullet. The increased RPM is what affects accuracy. The better ballance and stabilized the bulet is the higher the RPM it can be driven to and maintain accuracy.

Gearnasher from a post today on the CBF; "Now, for hunting with cast boolits, First the Mosin. It will take a lifetime to learn how to shoot gas checked boolits accurately at much above 1900 fps in that rifle, much less 2600."

Seems a bit of a reversal there for gear in this and the other thread here on AR. None whatsoever. You're taking a partial post out of context and twisting the meaning to misrepresent what I meant, and the reason behind my statement. This sort of deliberate word-twisting ranks right up there with theft, lying, and slander in my book and I'm sick of you doing this to me and others. Neither do I appreciate you responding to Joe by trying to start a personal fight again without adding a single, valid point or fact to the topic of conversation. Where I come from they call this being a TROLL. Seem he now agrees with me! Be that as it is Drop the God complex Larry, just because you make something up and present it as a statement of fact doesn't make it so. joe, why do you suppose it is so difficult to shot GC'd bullets accurately above 1900 fps in the Mosin 7.62x54R?

Larry Gibson

All right, for the rest of the story. A member at CB, who has never cast a bullet in his life, wants to make a hunting load in the 2600+ fps range for his military Mosin Nagant. He's read enough to know he "needs gas checks" or "paper patch" to achieve this, but what he hasn't the foggiest notion about bullet fit, loading cast, or anything. He's completely green. Telling him how to beat the balance monster won't do any good because he has no frame of reference yet, and I was presenting him a realistic picture of what he can expect to achieve with "standard" loading techniques, i.e. what the Lyman manual or others like it tells you. I also mentioned alloys and how cast bullets have a different range of ideal terminal performance than do copper-jacketed hunting bullets. I think I painted a realistic picture for him, which is what he needed.

So, WHY 1900 fps? For the reasons Joe stated, somebody who doesn't know what they're doing won't be able to achieve the things necessary to cast, load, and shoot a lead bullet out of a MN without having a mangled mess coming out of the muzzle. I never argued that mangled messes are usually terribly unbalanced and only shoot so-so at low velocities at best. Lower velocities don't exacerbate the effects that lack of throat support on the bullet, excess chamber neck clearance, poorly fitted, FL-sized brass, improper case neck expansion, poorly chosen components, and a myriad of other pitfalls have on cast bullet accuracy. You call it the "rpm threshold" because you attribute your findings to the rotational velocity of the bullet. I think that's a backward way of looking at it. The cause of the inaccuracy at higher velocities has to do with loading technique, not RPM. To say that you can "push the threshold upward" makes the threshold meaningless when one can take a bullet to 220K rpm with accuracy by correcting balance issues but your "threshold" maxes out (with typical loading methods) at 140K or so.

Everything has limits. Take a bolt-action .30-'06 10 twist, just about everyone that shoots has one. Load it with plain-based bullets, accuracy might be 1.5-2 moa and goes away at 14-1600 fps normally. Add a gas check, take it to 1900 fps with the same accuracy. Specialize the alloy and gain maybe another 150 fps. Correct the fit and some other things and shoot WD 50/50 alloy to 2400+ fps with even better accuracy, but it will peter out if you push it much faster(you don't know how to do this). Paper patch the same bullet, even with air-cooled 50/50 alloy, delete the gas check, and you can push it to the pressure limits of the cartridge with MOA or better accuracy. Each example has its own set of operating limits, and when you exceed them, the accuracy goes south. It ain't RPM that kills it, it's the inability at each limit point to continue to launch the bullet straight and balanced that kills accuracy. You may think it's the same thing saying "balance" or "RPM", and the two are connected, but only in the most abstract way. Balance isn't the only thing going on with the above examples that ruins accuracy above a certain velocity. You change twist rates around and can squeak more velocity with the same accuracy, but it isn't so much the RPM that's being sidestepped there, it's the LAND PRESSURE that's the bugaboo. Merely saying "It's the RPM that's the problem" is not only a poor description of the phenomena, it's a very incomplete one with too much variable range to have any real meaning. You have yet to realize fully what CAUSES the accuracy/velocity issue, and when you do you'll realize that attributing it strictly to rotational velocity of the bullet is no more conclusive than Richare Lee attributing it to alloy yield strength and peak pressure.

So, to be perfectly clear, the only thing we agree on is that there will be an accurate velocity limit to each particular gun/component combination.

JOE: I maintain that the principle cause (assuming everything else is done right) of the ultimate failure of a cast bullet to achieve accuracy beyond a certain velocity in any twist involves bearing surface limits and base squareness, particularly at muzzle exit. My reasoning is based upon the observed effects of paper jackets, copper jackets, and grease-groove bullets, particularly this last where I've recovered bullets that were shot at velocities beyond the "accurate limit" of the system and noted the engraves were obviously stressed and distorted on the drive side, and the bases were quite observably not square. This land distortion and square base effect was not observed on bullets fired accurately out of the same system at slightly lower velocity. I wish I had a good way to recover bullets, I might be able to actually say something conclusive about the relationship between twist rate, velocity, and this sort of bullet damage, but I've only recovered a few examples from two guns and two loads.

Gear

Yeah if we lived in Florida where there are places on the ocean front you can walk quite a ways out into the water before she really gets deep. They with a few friends as observers with hardhats on, we could shoot as straight as possible straight up and hope to recover the cast bullet when it falls back into the water. That bullet would tell us lots.

quote:

Originally posted by SmokinJ:
Yup, that's another possibility AC. Mann was a firm believer in the bullet getting kicked the wrong way at exiting the muzzle. Or perhaps even damaged by the exiting gas. I believe he only experimented with plain flat base bullets. We have it better today with are different alloys and gas checks.

My peers and I have been stressing all along minimum case neck clearance so that bullet base doesn't have much an area to move too and the gas also doesn't have much room to get around the base.

SmokinJ - I wasn't going to mention this because of the potential danger to not thorougly experienced shooters, but one of the things Mel Haris, David Lee and I did which helped us shoot winning BR groups and scores was:

Using "0" tolerance, interference-fit case neck ammo in our chambers.

We actually used loaded rounds where, with the bullet in the loaded case, the overall neck dimension of the loaded round was .0001" to .0002" LARGER than the chamber neck.

If it had not been for the camming ability of our bolt actions, we would not have been able to completely chamber our loaded rounds to fire them.

Not only were they more accurate than rounds with clearance around their necks, but they also allowed us to determine when a bullet was not the correct size to stay in the group when fired. A bullet which was a little too large would make the overall dimension of the neck enough larger that we could feel the difference when we chambered the round. We would NOT fire that round in a match, because it would almost invariably impact half a bullet diameter or a skosh higher in our group. And a round which chambered too easily would have a too small bullet which, when fired, might impact anywhere in or vaguely around our groups.

NOW THAT IS AGAINST ALL THE PRINTED RELOADING SAFETY RULES I HAVE EVER SEEN, ANYWHERE. SO I RECOMMEND AGAINST IT FOR ANYONE! AND A PERSON WOULD HAVE TO BE INSANE TO DO IT WITH A TOUGHER, JACKETED BULLET.

We did it for several years of cast bullet competition without any problems ever, but we knew what things should feel like going into our chambers. We also cut our chambers by "feel", using cartridge cases and bullets rather than chamber headspace gauges., so we knew exactly what we should be feeling as we closed the bolt.

Joe, I just realized that I have about 30 gallons of used engine oil stored in my shop, and a friend of mine owns a cabinet shop about half a mile from here and collects his tablesaw dust in a separate vacuum system from the planers, shapers, and sanders. I could get a couple 55-gallon drums of clean, dry, pine-free sawdust really easily. If I had the bucks I could build a long trough (16 feet maybe?) out of 2x12s with removable partitions every few feet, put a tin roof over it to keep out the weather, and we'd REALLY learn some stuff.