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Headspace. What's a few thousandths among friends?
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A client just brought in his latest acquisition, a brand new Ruger African rifle in 9.3x62. He had just come from the range where he found that Hornady ammo would not fire in the rifle but PPU ammo would fire every time. I checked with rifle's headspace with a "GO"gauge and found it to be perhaps .001" above minimum. Or nice & snug and within spec's. The PPU ammo that would fire would chamber with a .004" shim and the Hornady ammo would chamber with a .009" shim. The conclusion is that the Hornady cases are short in the headspace dimension to the point they will not fire. (Firing pin protrusion is .050".)

If there is a point(s) to all this it is that factory ammo is sometimes out of spec. and that headspace should be set with a gauge and not a cartridge case. Had this rifle been headspaced with the Hornady ammo, properly sized ammo from PPU and Lapua would not chamber.
 
Posts: 465 | Location: Fayetteville, GA | Registered: 12 August 2004Reply With Quote
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If there is a point(s) to all this it is that factory ammo is sometimes out of spec. and that headspace should be set with a gauge and not a cartridge case. Had this rifle been headspaced with the Hornady ammo, properly sized ammo from PPU and Lapua would not chamber.


You are correct, this is an excellent example of a topic we were recently discussing.
BB
 
Posts: 391 | Location: CANADA | Registered: 06 April 2004Reply With Quote
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Actually it does not tell you that at all; it tells you that both the ammo, and the chamber, were within SAAMI specs (voluntary), and neither the rifle chamber, nor the ammo is at fault.
If a .009 shim will close on Hornady ammo; that is well within spec.
Here are the numbers.
Max chamber: 2.098
Min ammo: 2.0809
Do the math and you will see that .0171 slop is allowed. Let's call it slop because is it not headspace. Most people do not realize that SAAMI specs are that generous.
The solution is to make the firing pin protrude more, easy on a Ruger. I like to see FP protrusion in the .065 range; like a Mauser. Those weak useless Mausers.
No guarantee that another factory barrel will be any better; after all, it is totally within spec.
I do sometimes fit barrels to accommodate someone's brass for a snug fit. No guarantee it will work with other make of brass.
 
Posts: 17045 | Location: USA | Registered: 02 August 2009Reply With Quote
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dpcd, why are you bringing logic to this? The correct answer is do things the instinctive way we've been trained/taught to think, and they'll magically work.

Your example of SAAMI specs is really borne out by magnum cartridges. I routinely chamber magnum cartridges so that they won't quite close on the go gauge. I've never measured a piece of factory magnum brass that wasn't .007 to .010 or more short of the go gauge. Some of it approaches .020". That, of course, is the reason that to make magnum brass last you have to resize it just enough to chamber again, and have it headspace on the shoulder instead of the belt. By short chambering it, you remove some of that "slop". And, since all factory brass has that slop, the rifle is still reliable.
 
Posts: 1098 | Location: Eastern Oregon | Registered: 02 December 2007Reply With Quote
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With that much "slop", it's a real wonder

there isn't a lot more problems crop up.

Thanks Tom, didn't know there was that much

tolerance.

George


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LM: NRA, DAV,

George L. Dwight
 
Posts: 5935 | Location: Pueblo, CO | Registered: 31 January 2006Reply With Quote
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OK dpcd, so you are saying that the rifle is at fault.
I actually find it very difficult to believe that SAAMI numbers allow ammo to be that small to cause the above condition as described by you. ( I have not verified industry numbers)
Sounds like the numbers are a little wishy washy to me.
BB
 
Posts: 391 | Location: CANADA | Registered: 06 April 2004Reply With Quote
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I didn't make them up; the numbers, are not "wishy washy" whatever that is. Believe it or not, it is reality.
Read the SAAMI specs and you will see. As dave said above, most magnums are in the realm of .018 clearance too. Nothing new, and it is a wonder that all our rifles, ammo, and dies work as well as they do.
I didn't say the rifle was at fault, the rifle is in spec (probably, I can't gauge it), as far as headspace goes; I proposed a way to fix it. Ruger FP protrusions are on the low side, again, compared to a Mauser, the standard I follow. On a custom rifle I would set the barrel back to match the users ammo. But on that Ruger, you have to go a full turn and then the stock will have a gap in it.
So, lengthening the FP protrusion will solve it, with the system he has.
Of course the absolute best way is to hand load and fit the brass to the chamber, as always taught here on AR.
 
Posts: 17045 | Location: USA | Registered: 02 August 2009Reply With Quote
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Hate to throw stones, but I've become pretty (No confidence" with Hornady ammo. Fire Hornady 450 Rigby ammo in a properly chambered rifle and case head expansion is a least alarming.

Conclusion...they use the same brass for 450 Rigby and 45t0 Dakota...just different head stamp
 
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In my books modifying a rifle to suit the ammo batch of the day does sound well wishy washy.
Something is off somewhere. Or am I missing something.
BB
 
Posts: 391 | Location: CANADA | Registered: 06 April 2004Reply With Quote
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In my limited experience, I've never seen magnum brass which was any less than .212". Given the minimum chamber dimension of .220 this is much less than .018. I don't believe I've ever measured a factory rifle which was over .223.
Typically, magnum brass has been around .214.
I chamber to .220. Rimmed cartridges are much the same although rims are generally held to closer tolerances. The minimum for most rimmed cartridges is .063 and that is what I chamber to.
With rimless cartridges, a little bit (one or two thou) of crush is still usable but rimmed cartridges won't compress so you don't want to risk it.
Generally speaking, I would not expect .010 of head clearance to cause misfires with .050 of firing pin protrusion. However, if you have .010 head clearance and the primer is seated .010 below flush (deep primer pocket), you are down to .030 of potential penetration which is pretty borderline. Regards, Bill
 
Posts: 3490 | Location: Elko, B.C. Canada | Registered: 19 June 2000Reply With Quote
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Mr bull; something is off? Are you missing something? Yes, maybe reality. But not if you look at the details of the matter, and I just go with the facts. Nothing else. And the facts, as I see them presented in this case, and applying the allowable tolerances as specified in the SAAMI specs (and realizing that no maker of anything has to even read them), the facts are that both that guy's rifle, and his ammo, are both within those specs.
Easy to understand how it can happen. Sometimes the planets align wrongly.
Fortunately most makers try to stay in the middle of the specs.
And Mr Leeper, that is exactly what is happening as I see it; .050 won't fire that ammo, although everything is within spec. But also, magnum brass and chambers are allowed to vary far more than what you have seen. You are lucky.
Who do you blame? Rifle, or ammo? The facts show, no one is at fault.
 
Posts: 17045 | Location: USA | Registered: 02 August 2009Reply With Quote
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DPCD is correct--the potential clearance between cartridge and chamber ("tolerance stack-up") is as he relates. Why is this?

SAAMI's job is to define dimensions and tolerances--two different things--that ensure, for example, that shotshells made in Italy will fit and function in a shotgun made in the States, providing both meet SAAMI standards. This holds true for rifles, pistols and their ammunition as well.

SAAMI also defines working pressures of firearms, and the manner in which these are measured, as well as defining "proof" loads for each caliber in its standardized "library".

There's no question that problems such as the one described by the OP occur from time to time, but, in the main, while many curse at "sloppy" chambers, SAAMI does a very good, comprehensive job to ensure the safe functioning of firearms and ammunition.

Dave Manson
 
Posts: 678 | Location: Michigan | Registered: 04 November 2007Reply With Quote
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Good thread, I learned something. Brian


IHMSA BC Provincial Champion and Perfect 40 Score, Unlimited Category, AAA Class.
 
Posts: 3335 | Location: Kamloops, BC | Registered: 09 November 2015Reply With Quote
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As beautifully made as MS rifles are, their headspace can be all over the map. If it wasn't for long FP protrusion, many wouldn't fire factory ammo.
 
Posts: 6830 | Registered: 10 April 2009Reply With Quote
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Check out headspace tolerance for 45 Auto and 9mm Luger if you'd like to see "tolerance". Good thing the original weapons firing those rounds had looong inertial firing pins.

Dave Manson
 
Posts: 678 | Location: Michigan | Registered: 04 November 2007Reply With Quote
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After the first shot and its off a tad, its probably a good idea to set the bullet out to touch the lands, in effect you will be fireforming the case to match the chamber..Most of the time I just shoot the round and it fireforms itself without my help..Sometime we overthink these situations but maybe thats not a bad idea..Most of old timers still fly by the seat of our pants, some admit it and other act horrified, now thats impressive!! jumping


Ray Atkinson
Atkinson Hunting Adventures
10 Ward Lane,
Filer, Idaho, 83328
208-731-4120

rayatkinsonhunting@gmail.com
 
Posts: 41758 | Location: Twin Falls, Idaho | Registered: 04 June 2000Reply With Quote
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I worry about the Ruger's mainspring. We've got an FN Mauser with 12 thou headspace but it always fires. On the other hand, a buddy got a s/h Ruger 9.3x62 and it failed to fire the first three times. A bit of oil seemed to fix it - but it should not be that sensitive IMHO.

Anyway, I notice the mainspring is a bit skinny compared with Mauser's.
 
Posts: 4915 | Location: Melbourne, Australia | Registered: 31 March 2009Reply With Quote
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Good point on the 9mm and .45acp. I have often thought that if I were going to build a 9 or .45 for maximum accuracy I would fit an unchambered bbl. to the slide and then short chamber it to the point that I would use only trimmed brass. I have never measured a 9mm or .45 case that came even close to minimum chamber dimensions.
C.G.B.
 
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They have to function reliably and it doesn't matter in a pistol.
As for Ruger mainsprings; I find them to be strong enough; it is the FP protrusion that is the issue. I have had them at .045; Way too short. No amount of spring tension can make up for the firing pin not reaching the primer deep enough.
As I said, it is easy to make them longer though.
 
Posts: 17045 | Location: USA | Registered: 02 August 2009Reply With Quote
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quote:
The PPU ammo that would fire would chamber with a .004" shim and the Hornady ammo would chamber with a .009" shim. The conclusion is that the Hornady cases are short in the headspace dimension to the point they will not fire. (Firing pin protrusion is .050".)


the case does not have head space; I off set the length of the chamber with the length of the case from the datum to the case head. Before I left for the range I would have know the difference in length between the PPU and Hornady when measured from the datum/shoulder to the case head.

quote:

Do the math and you will see that .0171 slop is allowed.


.0171" is .0031" over field reject length for the 30/06.

quote:
Nothing new, and it is a wonder that all our rifles, ammo, and dies work as well as they do.


I have dies and shell holders that are 60+ years old, I do not have a die and or shell holder that is as sloppy as you describe.

F. Guffey
 
Posts: 453 | Location: Dallas, Texas | Registered: 16 February 2010Reply With Quote
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Cartridge cases do indeed have a headspace dimension & it's measured just like the headspace dimension in a chamber, i.e., from the cartridge head to a magical datum point on the shoulder (rimless bottlenecked cartridge). You will forgive the obviously sexist metaphor that a rifle chamber has female headspace and a cartridge has male headspace. That's why SAAMI establishes min/max dimensions for BOTH cartridges and chambers. What joy when they find compatibility in properly made firearms and ammunition!

As for determining cartridge measurements before going to the range, God bless you. My client, however, is not a hand loader--I know there ought to be a law that all rifle shooters are hand-loaders with a fully equipped machine shop at their service. The gun's owner committed the sin of trusting a brand new factory rifle to fire factory ammo. He had every right to expect the rifle, even a Ruger, to go bang everytime the trigger was pulled.

I will not publicly acclaim that DPCD was right about firing pin protrusion. Such might cause gloating. I will admit that the Ruger firing pin has been adjusted in my firing pin stretcher and that it protrudes a proud .063". It suspect this will be enough to fire the Hornady ammo & all will be right with the world.

Cheers & thanks for all the replies.
Roger
 
Posts: 465 | Location: Fayetteville, GA | Registered: 12 August 2004Reply With Quote
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Very good job Roger.
I was certain you would unf*ck it.
Mr guffy; the OP was not talking about a 30-06, which has different specs than the 9.3.
 
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The gun's owner committed the sin of trusting a brand new factory rifle to fire factory ammo. He had every right to expect the rifle, even a Ruger, to go bang every time the trigger was pulled.


I believe Ruger should have had an opportunity to test the rifle. I do believe if the rifle required a longer firing pin they should have an opportunity to agree and or disagree.

I do not agree with the only standard is bang and if it does not go bang make the firing pin longer.

F. Guffey
 
Posts: 453 | Location: Dallas, Texas | Registered: 16 February 2010Reply With Quote
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quote:
Mr guffy; the OP was not talking about a 30-06, which has different specs than the 9.3.


OK, The firing pin did not reach the primer, that means nothing to you but I want to know where the case is when the firing pin bust the primer.

F. Guffey
 
Posts: 453 | Location: Dallas, Texas | Registered: 16 February 2010Reply With Quote
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At the risk of getting lambasted, is there an industry standard for firing pin protrusions?
BB
 
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At the risk of getting lambasted, is there an industry standard for firing pin protrusions?


I can not believe no one checked the specifications. I believe we have found the fiddle case. They have a cute little saying that covers the fit between the case and chamber; they claim the case can fit the chamber like rat scat in a fiddle case.

F. Guffey
 
Posts: 453 | Location: Dallas, Texas | Registered: 16 February 2010Reply With Quote
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Dear Mr. big bull,
Fear no lambasting from me. If there is a chisleled-in-steel standard for firing pin protrusion, I haven't found it. I have seen everything in print from .050" to .070". The best answer is, I guess, is that it depends on the action design and its application.
For a true benchrest/target rifle where Both headspace and ammunition tolerances are held to 1/10th of a frog hair, .050" protrusion is OK, as is small diameter, bushed firing pin tips. For hunting rifles, especially those built on one of Tom's old, worthless and obsolete Mauser actions, more protrusion is needed to compensate for more generous tolerances in chambers and factory produced or military ammunition. Personally, I have found .060 to .065" to be quite satisfactory.

On a strictly personal note, I prefer guns with no headspace or firing pin protrusion considerations. My last assignment as a Field Artillery officer was with M110A1 203mm (8" bore diameter) howitzers. With bagged, separate loading ammunition there was no headspace or firing pin protrusion to worry about, & there was no doubt when the thing fired.
 
Posts: 465 | Location: Fayetteville, GA | Registered: 12 August 2004Reply With Quote
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Wise words, Roger. As usual. But you have to watch those Cannon Cockers.
For others, no, there is no spec for firing pin protrusion for sporting rifles. Each maker designs his own, but about .055 or so is normal. Of course, all military arms have specs, and for an M16 is I recall .028-.036.
As for not understanding how Ruger test fired that particular rifle, they obviously didn't use the same ammo as the owner did.
I see and understand that it is hard for some to comprehend how such a thing can happen here, and now, but, back to the facts, one only needs to look at them to see that it can, and did, happen. As Dave eloquently said, Tolerance Stack Up, and he should know; he makes all the reamers.
And in the case of the 9.3x62, it is an old German round, only recently spec'd by SAAMI and I can only guess that the generous tolerances are so it will fit old rifles. I do not know; they didn't ask me.
Still don't understand the violin thing. SAAMI specs are not haphazardly arrived.
Guys, this is a very extreme case/example. Do not fret over it; it won't happen to you. (If it does, I will advise on COA.)
And I do not know what lambasting means; Tankers do not use words that long.
 
Posts: 17045 | Location: USA | Registered: 02 August 2009Reply With Quote
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Wise words, Roger. As usual. But you have to watch those Cannon Cockers.
For others, no, there is no spec for firing pin protrusion for sporting rifles. Each maker designs his own, but about .055 or so is normal. Of course, all military arms have specs, and for an M16 is I recall .028-.036.
As for not understanding how Ruger test fired that particular rifle, they obviously didn't use the same ammo as the owner did.


Ruger designed the rifle to use minimum length/full length sized ammo when measured from the shoulder/datum to the case head. It just proves Ruger can not protect the shooter from himself. Someone has added .013" to the protrusion and now the firing pin can reach the primer on cases that are no-go gage length and .001" short of a filed reject length.

Back to "I want to know where the case is located in the chamber when the firing pin crushes the primer". I understand that is not your problem but there is a chance the case was shoved too far forward for the extractor to jump the rim of the case. And then there is that other insignificant 'thing'; when the firing pin strikes the primer I want the head of the case against the bolt face.

I understand that is not something you would concern yourself with but I want to know where the case is located in the chamber when things get serious.

F. Guffey
 
Posts: 453 | Location: Dallas, Texas | Registered: 16 February 2010Reply With Quote
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Mr G; you need to read the SAAMI specs. Hornady made that ammo IAW them. Ruger made the rifle, IAW them. Ruger did NOT build the rifle to shoot absolute minimum length ammo; obviously. They make it to shoot average length ammo, not minimum. Everything in manufacturing is designed to be optimized, not customized to one end or the other of the specs. That is why we have custom gunsmiths. I make them absolute gauge minimum and sometimes below that.
They are looser than anyone would like, but they are, what they are.
You reference dimensions and gauges that are not germane to the 9.3x62. It has no field reject criterion.
Cases that are no-go gauge length??? I don't get that one.
Not a perfect world.
I, too, want the case head firmly against the bolt, and I make all my ammo to do so. However, in the real world, SAAMI is not so concerned about that; they allow some very loose tolerances, magnums are the most egregious (with the 9.3 it appears); again, read the book.
You should write to SAAMI expressing your concern; they do make changes all the time to their data base. Telling me won't help at all; I have no influence over them. I am just outlining what the facts on the pages are.
My only opinion is, I like, and make, firing pin protrusions on hunting rifles, of at least .060-065; the Mauser standard.
 
Posts: 17045 | Location: USA | Registered: 02 August 2009Reply With Quote
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quote:
No confidence" with Hornady ammo.

Having been a handloader since 1965 I actually have relatively limited experience with factory loads for centerfire rifles. However, the only factory loads I've ever experienced difficulties with was Hornady brand -- in two different calibers and loadings.

However, I recently hunted Africa using the local guide's rifle and ammunition. The ammunition was the cheap Hornady "American Whitetail" 140 grain .270 Win. Not only was it dependable and accurate, but took down game which is "supposed" to be too large to hunt with a .270.

So, I class Hornady ammunition as neither "good" nor "bad" but simply "uneven". As I say, being a handloader, the quality of factory ammunition isn't really an issue that keeps me awake nights.
 
Posts: 13214 | Location: Henly, TX, USA | Registered: 04 April 2001Reply With Quote
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How does one increase the firing pin protrusion on a Ruger Hawkeye?
I might give it a go.


"The liberty enjoyed by the people of these states of worshiping Almighty God agreeably to their conscience, is not only among the choicest of their blessings, but also of their rights."
~George Washington - 1789
 
Posts: 2135 | Location: Where God breathes life into the Amber Waves of Grain and owns the cattle on a thousand hills. | Registered: 20 August 2002Reply With Quote
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PM me and I will go over it with you.
It is for a machinist. It is not something to be taken lightly.
 
Posts: 17045 | Location: USA | Registered: 02 August 2009Reply With Quote
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Thank you sir. Iwl do that though not a machinist. Often wish I were though.


"The liberty enjoyed by the people of these states of worshiping Almighty God agreeably to their conscience, is not only among the choicest of their blessings, but also of their rights."
~George Washington - 1789
 
Posts: 2135 | Location: Where God breathes life into the Amber Waves of Grain and owns the cattle on a thousand hills. | Registered: 20 August 2002Reply With Quote
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You should write to SAAMI expressing your concern;


I have said from the beginning the case does not have head space. After that everything had head space and and ever tool was a head space gage. L. Willis advertised a digital head space gage and reloaders got all giggly. All of the tool manufacturers called his head space gage 'a dial indicator stand'.
quote:
Mr G; you need to read the SAAMI specs. Hornady made that ammo IAW them. Ruger made the rifle, IAW them. Ruger did NOT build the rifle to shoot absolute minimum length ammo; obviously. They make it to shoot average length ammo, not minimum. Everything in manufacturing is designed to be optimized, not customized to one end or the other of the specs. That is why we have custom gunsmiths. I make them absolute gauge minimum and sometimes below that.[/QUOTE]

I make a gage that I call 'short chamber' it is not my problem but SAAMI does not have a 'zero', all they have is plus and minuses because of their tolerances. Because I have a zero I am able to form cases that are .012" shorter than a minimum length chamber. that would be .007" shorter than a go gage length chamber.

I have read SAAMI, insisting I read it again will not cause me to agree with you. the Ruger was a new rifle, both boxes of ammo used were new. The difference in length between the PPU and Hornady when measured from the datum on the shoulder to the case head was .005".

quote:
The conclusion is that the Hornady cases are short in the headspace dimension to the point they will not fire. (Firing pin protrusion is .050".)


OK, I am at home when I get a call from a firing range, they claim a shooter has a new Ruger with two new boxes of Remington ammo. They say the shooter had 5 rounds that failed to fire and 15 that did fire. I told them to call Remington I also informed them the phone number for Remington was on the box.

In the meantime the man with the Ruger tried to bust the primers 3 times each he then passed the ammo to 3 30/06 shooter; they made at least two attempts each at busting the primers, no luck.

That evening a man shows up with a box of Remington 30/06 ammo with 5 failed to fire rounds and 15 cases that did fire. I measured and weighed each case and round, I then pulled the bullets and weighed the bullets and powder, I removed the primers and then reinstalled the primers, I dug out one of my primer busting rifles and chambered the cases with primers; I then busted the primers one at a time.

It was about that time I ask for the phone number of the shooter; no phone number. In my opinion the cases were in magnificent condition. All of the weights measured to the grain. The case measurements came out to the .001". There were no protruding primers on the 5 failed to fire cases after removing and reinstalling the primers.

I would like to have formed 20 cases for the 30/06 chamber with 4 different case length from the datum to the case head. I would have started with cases that were go-gage length, no go-gage length and field reject length cases.

Out of all of that I could have told him the length of his chamber from the datum to the bolt face.

quote:
So, I class Hornady ammunition as neither "good" nor "bad" but simply "uneven". As I say, being a handloader, the quality of factory ammunition isn't really an issue that keeps me awake nights.


Good, I only have two boxes of new, over the counter ammo, both boxes are Hornady.

F. Guffey
 
Posts: 453 | Location: Dallas, Texas | Registered: 16 February 2010Reply With Quote
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Sambarman,
Not common but I have seen many new in the box guns fail to fire because of caked dryed grease in the bolt, and it slows the thrust or grabs and holds the bolt, clean the bolt is best, but just a bit of oil usually works...seldom if ever a severe problem and an easy fix in every case I have seen or had happen to me...My latest Ruger 220 Swift failed to fire out of the box, It was a NIB mod 77 in the box since 1973 or ?? I loaded it with WD-40 I had on hand and blew it out with a pressure hose and started shooting awesome groups and no misfires..cleaned it good later that day..


Ray Atkinson
Atkinson Hunting Adventures
10 Ward Lane,
Filer, Idaho, 83328
208-731-4120

rayatkinsonhunting@gmail.com
 
Posts: 41758 | Location: Twin Falls, Idaho | Registered: 04 June 2000Reply With Quote
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Definitely a lot of "slop" in SAAMI specs.
I just finished building a .300 WSM, and the "customer" in this case happened to be my son Smiler.

He texted me that his fired brass was measuring 1.736 with his comparator, while the new Norma brass was at 1.728-1.730.

I freaked out a bit because that seemed way excessive- so I measured the Manson go gauge, and it came out at 1.734. I'm sure the gauge is correct (I can't actually get a datum measurement unless I make a custom bushing for the .445 datum diameter).

My experience is that Dave's gauges are at the minimal end of the allowed range- meaning the Norma brass is something around .005 under minimum. Definitely a bit of stretching on the first firing...
 
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Hello Big Gorilla:

For your--and everyone else's reference--we make our headspace gauges for rimless, shouldered calibers to the below dimensions and tolerances:

"GO"-min SAAMI (or CIP, if no SAAMI std) +.0005"

"NO GO"-"GO" plus .006" + or - .0003"

"Field" SAAMI Max (usually min plus .010", +.0000", -.0005"

The above gauge dimensions and tolerances are designed to ensure that the gauges you use fall within the industry min and max for headspace.

Measuring headspace gauges isn't about their overall length--except for rimless pistol calibers (9mm Luger). Dimensions are taken from the base of the gauge to a specific datum diameter on the shoulder of the gauge. Unless one has the correct datum gauge, the most that can be said with certainty is that one fired case is longer to the shoulder than another. Comparisons can be made, but specific dimensions are impossible without the correct equipment.

Hope this helps,

Dave Manson
 
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This problem almost caused a war between Sweden and Norway. The union caliber 6,5*55 was adopted by both Sweden and Norway as a united kingdom, but the unity were breaking up and troups were called in to be prepared. One of the reasons of anger were the norwegian ammunition couldn`t camber in the Swedish M96 but the Swedish ammunition could chamber in Norwegian Krag-Jörgensens, it was resolved when they found out both rifles and the ammunition were within specification but on opposite end of it.
 
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Originally posted by DManson:
Hello Big Gorilla:

For your--and everyone else's reference--we make our headspace gauges for rimless, shouldered calibers to the below dimensions and tolerances:

"GO"-min SAAMI (or CIP, if no SAAMI std) +.0005"

"NO GO"-"GO" plus .006" + or - .0003"

"Field" SAAMI Max (usually min plus .010", +.0000", -.0005"

The above gauge dimensions and tolerances are designed to ensure that the gauges you use fall within the industry min and max for headspace.

Measuring headspace gauges isn't about their overall length--except for rimless pistol calibers (9mm Luger). Dimensions are taken from the base of the gauge to a specific datum diameter on the shoulder of the gauge. Unless one has the correct datum gauge, the most that can be said with certainty is that one fired case is longer to the shoulder than another. Comparisons can be made, but specific dimensions are impossible without the correct equipment.

Hope this helps,

Dave Manson



Thanks, Dave. Exactly as I figured.
I was just a bit surprised that the Norma brass was that much under "go" mimimum.

Commonplace to set HS so that light resistance on bolt fall is felt on the gauge, but I don't know of anyone that intentionally sets HS thousandths under "go". Just seems unnecessary to stretch the brass right out of the box, even in a minimum headspace chamber.
 
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