M94 Extruded Primers

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  • Last Post 31 March 2024
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Aaron posted this 23 March 2024

I have two IDENTICAL Cimarron Arms (Uberti) Model 94 rifles chambered in .38-55 Winchester. After filing a radius at the 6 o’clock position on the breech face, both rifles now feed ammunition without a hitch. While shooting the second rifle last week, I noticed that it simply would not open the action after the shot. It was jammed up tight.

The load is a very moderate load with Starline 2.085” (short) brass. The propellant is 28gr of IMR-3031, a Hunter Supply 260gr FP bullet, and lit off with a Winchester Large Rifle primer. This was the third such load tested in the rifle with the same result. Propellants varied on previous loads with Buffalo Rifle, RL7, A2520, and another with a propellant I can’t recall at this writing.

ALL of the loads resulted in a jammed-up action which could not be opened with normal force on the lever. To get the fired cartridge out of the chamber I had to cock the hammer and drop the hammer on the fired case. The lever could then be operated in the usual manner and the fired case extracted. Once ejected, the backed-out primers became visible. The primers are extruding at least .015” and may have been seated a tad deeper with the firing pin strike on the fired case.

A focused internet search on M94 backed out primers seemed to yield a consensus of a Headspace issue which was(is) endemic to the M94 family of rifles. Of course, there were dissenting opinions which ran the full gambit from Alien interference to dirty chambers. Rest assured, my chamber is “normal” and operating pressures are within industry standards.

I am believing the headspace argument is valid based on a few things:

  • Winchester made thicker locking bolts to accommodate headspace issues in decades past. A .005” thicker locking bolt was normal and can still be purchased on various sites.
  • When my bolt goes into battery, I can use my thumbnail to push it forward just enough to be visible. The locking bolt also appears to rise just a little bit too. That could be my imagination, but it does seem to rise a bit and hold the bolt forward.
  • The Starline .38-55 brass I have is measuring .056” rims and not the .063” as called for by SAAMI. Not as thick as they could be, but not by much.
  • My measurement for headspace is .071” or 1 thou greater than the SAAMI spec.

One thing is certain, the SAME cartridges fired in the first rifle DO NOT have extruded primers. The bolt on the first rifle can not be manipulated forward on that rifle either. Two identical rifles. One extrudes primers, one does not.

I have to say the headspace argument is correct although I have to admit, I do NOT see how excessive headspace will allow a primer to extrude. That case is going rearward when fired and should seat that primer flush, if anything, with the case head. I simply can’t envision it in my feeble little brain.

I may order a “Field” gauge to see if the action will close on it, but still have a few comparative tests to make before I spend even more money. I’ll try the 2.125” brass to see if it also extrudes primers. It could be the brass primer pocket with this lot of Winchester primers is incompatible. Like I say, a few more tests are in order.

Do any of you who shoot a M94 and have experienced extruded primers have any input here?

Rifle-1, Extruded Primers

Rifle-2, Normal Primers, Same Load

 

With rifle in hand, I confidently go forth into the darkness.

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Premod70 posted this 31 March 2024

Thanks Wilderness, I looked three times and missed it every time. Time for my afternoon nap:-).

Forrest Gump is my smarter brother.

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Wilderness posted this 31 March 2024

Original post, third paragraph, .015".

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Premod70 posted this 30 March 2024

Another point of curiosity is the remaining measurement not stated is the protrusion of the fired primer.

Forrest Gump is my smarter brother.

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pat i. posted this 30 March 2024

The rim thickeness of the case min = .063 and max = .073

Actually the case rim thickness spec is .063 - .010, in other words.053 to .063 so the cases are well within spec.

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Aaron posted this 30 March 2024

Aaron you know what the SAAMI drawing specs say?   The rim thickeness of the case min = .063 and max = .073, but the their measurement from the bolt/breech measurement (which is this case being a rimmed cartridge is the headspace) is min = .063 and max = .070. Hmmm that doesn't sound just right. You can look it up on SAAMI specs for center fire cartrdiges.  It's the same measurements for the 375 Winchester.   Confusing isn't it?

No confusion whatsoever. The measurement (gauge) is a binary measurement tool. It will or it will not. Yes or No. A one or a zero. It does not display continuous data, it reports discreet data. If the gauge rim thickness was .070" (the max SAAMI tolerance for 38-55 headspace), and the bolt closed on the gauge, is the headspace actually at the maximum or over the maximum? With the gauge set to .071" and a bolt closure, one can say the headspace is OVER maximum. By how much is irrelevant at this point. We simply wish to know a discreet piece of data - is the headspace OVER maximum or not.

I think at this point, we are beating a dead mule. We should probably let this thread die off since we are way off topic now. I have stated my belief of the tolerance stacking theory for the extruded primers since going with another brand of primers cured the problem in Rifle-2, which was never a problem in Rifle-1 with its differing chamber.

Have a great day and shoot safe!

 

 

With rifle in hand, I confidently go forth into the darkness.

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MP1886 posted this 30 March 2024

Aaron you know what the SAAMI drawing specs say?   The rim thickeness of the case min = .063 and max = .073, but the their measurement from the bolt/breech measurement (which is this case being a rimmed cartridge is the headspace) is min = .063 and max = .070. Hmmm that doesn't sound just right. You can look it up on SAAMI specs for center fire cartrdiges.  It's the same measurements for the 375 Winchester.   Confusing isn't it?

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Aaron posted this 30 March 2024

Hey Aaron, curious to know the rim thickness of the no-go gauge.

It's .071" on the button. For the doubters out there, here are images of the measurements.

So, when I went to school .050" + .018" + .003" = .071"

 

With rifle in hand, I confidently go forth into the darkness.

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Aaron posted this 30 March 2024

Mark….I like that term “tolerance stacking”. It seems that it is what is going on in Rifle-2 where its chamber, and all the other components, allow primer back-out. Rifle-1 must have a different chamber which is not contributory to the stacking phenomena.

 

 

 

With rifle in hand, I confidently go forth into the darkness.

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MP1886 posted this 30 March 2024

When  you have constant leakage you get pitting in the ring you see. What you are seeing is friction wear and remember the primer is pushing back on the bolt face too.  The ring is the gap between the round corners of the primer and the round corner of the primer pocket mouth. That's why the you get the ring because that gap doesn't wear anything, if you understand what I mean. 

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MarkinEllensburg posted this 30 March 2024

Right now over on the Accurate Shooter forum some people are having issues with Winchester LR primers. Mainly gas leakage around the primer edge etching the bolt face.

How interesting. When I was in my 20s and buying rifles my Dad mentioned that you can tell from a bolt face how much a rilfle has been shot by the ring around the firing pin. I am guessing years later that there likely is a small amount of gas leakage past primers even under ideal specs for that to be an issue.

I am currently using Remington primers that are very hard to seat. I can't seem to reliably seat them below flush with my primer arm on my RCBS Rockchucker press. Lee's early hand prime works just fine though. Anyway last match I believ I was seeing gas leakage around some primers. I seriously wonder how many 1000's of rounds it takes for gas cutting of a boltface to be an issue.

I think what Aaron is seeing is a case of excessive headspace due to tolerance stacking. It seems he has found the solution by adjustment of components.

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Aaron posted this 30 March 2024

Mabye you do have lousy newer WW primers, but you didn't answer why your other rifle firing the same ammo didn't have any problems. 

We may never know. Different chamber I suppose. 

With rifle in hand, I confidently go forth into the darkness.

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MP1886 posted this 30 March 2024

All the Winchester primers I shot were the silver ones also.  Then I switched brands because of costs. 

Aaron I'm sure you mean you had blow by with your WW primers in a 7.62x54R cartridge instead of 7.72. Hey just jabbing you, that's all.  Mabye you do have lousy newer WW primers, but you didn't answer why your other rifle firing the same ammo didn't have any problems. 

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Aaron posted this 30 March 2024

Hey Aaron, curious to know the rim thickness of the no-go gauge.

I'll get that for you tomorrow. I have buttoned up the shop for the evening. Remind me if I forget to post that for you.

 

With rifle in hand, I confidently go forth into the darkness.

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Premod70 posted this 30 March 2024

Hey Aaron, curious to know the rim thickness of the no-go gauge.

Forrest Gump is my smarter brother.

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Premod70 posted this 30 March 2024

Hey Aaron, curious to know the thickness of the no-go gauge.

Forrest Gump is my smarter brother.

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Aaron posted this 29 March 2024

Right now over on the Accurate Shooter forum some people are having issues with Winchester LR primers. Mainly gas leakage around the primer edge etching the bolt face.

And sure as heck, a few months ago I was getting gas blow-by on my WW primers. It was the 7.62x54R. I KNOW the pressure wasn't the culprit and was scratching my tiny little head about it. Good to know. Thanks for the post Admiral

 

 

With rifle in hand, I confidently go forth into the darkness.

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admiral posted this 29 March 2024

Right now over on the Accurate Shooter forum some people are having issues with Winchester LR primers. Mainly gas leakage around the primer edge etching the bolt face. They had this issue about 10 years ago with some lots and were taking them back and issuing refund checks. After having it happen to me Winchester paid to have my bolt face bushed. I returned a case (5000) of LR primers to them for a refund. It was like $135, those were the days, lol. Winchester did decrease their primer dimensions, we're talking a few 10,000's, for easier function in progressive reloading presses. This was reported in Handloader magazine a decade ago by, I think, John Barsness. I haven't shot millions of Winchester primers as MP1886 has but have shot hundreds of thousands of Winchester LR primers since the early '80's and never had any issues with the older style silver colored primers. I don't like the brass colored Win LR primers and will not use them anymore.

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pat i. posted this 29 March 2024

There's another gauge that I bet most of you don't know about and it's called a "manufacturing gauge.

Pray tell what's a "manufacturing guage? Don't be man of 1000 secrets, it gets annoying. We all love learning new things. I've probably chambered 20 barrels for my own use and never heard of one. And a search on the internet and reamer makers turned up nothing.

Aaron I couldn't agree more about the Lee tool. Use that thing to seat Fed primers for a couple of months and you'd be unbeatable in a thumb wrestling contest. I use my Sinclair hand primer when playing with those hard to seat primers. It does the job with ease.

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MP1886 posted this 29 March 2024

Aaron essentially what you said about the field gauge is exactly what I said, except I said it a different way. There's another gauge that I bet most of you don't know about and it's called a "manufacturing gauge".  

The field gauge is the militarys way of basically allowing a rifle out in the field that shouldn't be in my opinion.

 

Used Winchester primers by the millions, never had a problem with them. My most offending primers have been CCI. 

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Aaron posted this 29 March 2024

The WW are a lot easier to seat too. Don't know if it's diameter or just harder cups but that's my experience and maybe why with the Lee hand primer tool they tell you not to use Federal primers.

Absolutely agree. WW primers seat easily. CCI are the worst and my thumb gets squashed when using the Lee Auto Prime hand tool. I ended up getting a RCBS Automatic Priming Tool. Glad I did. My thumbs are now normal size and this rascal seats any primer easily with its mechanical advantage. The Lee hand prime tool is the easiest to use but man, it does a number on your thumbs.

 

With rifle in hand, I confidently go forth into the darkness.

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