Case Head Separation in Mosin-Nagant.

M

Mosin-Marauder

New member
Hello all,

I loaded 18 rounds of 7.62x54R for my Mosin, today. I used a load of 51.2 Grains of H 4350 under a 180 grain Speer Hot-Cor, this load shot well the first time, so I figured I would load a bit more and change to match primers. I took it out to the range and got three shots fired when all of a sudden I had extreme difficulty working the bolt. I finally "mortared" it on the ground and all that came out wad the case head. I got it home and managed to get the remaining case out with the Mosin cleaning rod. Accuracy was awful, three shots strewn about the target, from a load that managed to get 4 shots under 2 inches at 100 yards. My rifle seems sound, no obious cracks in the chamber that I can see (I haven't looked too much). These winchester cases have been through about 5-6 loads, some being younger. I have no idea what prompted it to do this, but I am looking for any advice. I weighed each charge on my digital scale before I shot and none exceeded anywhere near Max charge. Should I throw these loads And start with fresh brass? Any advice as to why this may have happened would be appreciated. This is the first time this has happened, so im sure itd not the gun.
Thanks.

Regards,

-Mo.
 
How you FL sizing your brass each time you load it. Also I'm willing to bet that your mosin has a "large spec" chamber and isn't exactly set minimum on its head spacing. All three things added together will ruin brass much quicker than anything else.
 
You might be over working the brass. I'd take a fired piece of brass and slowly work your die down until it chambers with no resistance then lock it down and leave it. That will prevent from working the brass anymore than necessary and may give you some more life out of it.
 
5-6 loads for some rifles is about all you will get. I usually start checking for "the ring" around that point with most. Its the ring on the inside at the base of the case where it separates. Its caused by the cases brass "flowing" when fired. I use a paper clip with the end sharpened and with a slight bend on it as a tool to check mine.

Do you check the OAL of the cases after you size them? That will give you an idea if the brass is flowing. If youre seeing cases needing trimming each load, thats a hint something might be up with your headspace. Not necessarily anything "wrong", but it bears watching so you know when to trim and check on things anyway.

Out of habit, I trim all cases in a lot/box if I need to trim one. That also helps with keeping all things even.

Headspace on some of the mil surps can be a little on the full size. I had a SMLE that would have head separations on the first reload of commercial brass and was not one I reloaded a lot for because of it. You could take your rifle to a gunsmith and have the headspace checked. That would answer some questions and maybe guide you in the right direction. 5-6 loads on a piece of brass isnt really all that bad though. Its about what I used to get with my HK 91's with any brass, and my M1's, M1A's when using military brass usually didnt make it past 8.
 
This was one fired brass too, so add that and I'm probably near 8 uses. I have some new brass that, once I finish firing this batch of loads, I will toss the old brass and use.
 
This was one fired brass too, so add that and I'm probably near 8 uses.
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Im a little confused. When you say "one fired", are you saying the separation happened on the first reload?

Are you using that "new math"? :D
 
Got ya. :)

8 reloads doesnt sound unreasonable then. I would still check the other cases and see if you feel (sometimes you can see it with a flashlight) the ring in them. If you come across more, then youre likely near scrapping them at that number.

This kind of thing is why its important to keep track of lots or boxes of brass and keep records of what goes on with what. That can be a challenge sometimes, especially if you use the same brass in different guns. If you load for more than one gun in the caliber, you may want to dedicate a box or two to it, and keep track of things until you have a better understanding of whats going on.
 
I fired five rounds again today and had another seperation, luckily outside the gun. After I finish this bunch of loads, I'm scrapping this brass. Hopefully the Prvi/Grafs brass I have on hand will be good.
 
I would guess you are over sizing the brass. Buy a case gage that measures from base to shoulder datum.

The difference for fl sized brass should be fired -0.003" on average.

Since a Mosin is likely loose, I would guess you are approaching -0.010". You could also loose the FL die 1/8 turn with a new case each time until it is tight to close the bolt and then tighten 1/8 turn for a good fit.
 
I somewhat doubt it is a sizing issue, as I've used this same process for 8 reloads on some cases, and the separation only happened in the older ones. There's no difficulty working the bolt before or after being fired, aside from the usual bit of stiffness that comes naturally with Mosin rifles. Plus, headspace wouldn't be an issue, as it headspaces of the rim, not the shoulder. And headspace has been checked. I will turn my die in a quarter of a turn the next time I load just to make sure it is FL sizing, thoughm

I also read (maybe in a Lyman Manual) that the average case life for rimmed cartridges is somewhere between 8 and ten, including the original loading. And this isn't the best brass so I would say it's just this batch's time to go.
 
Mosin-Marauder
I screw the die down until it touches the shellholder, lock it in place and then size them all.
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How many firings until case head separation?
You might increase that number by backing the die adjustment a little out of the press, so the shoulder only gets pushed back .002", .001", or .000".
 
Normally, the 7.62×54R headspaces on the rim and FL resizing wouldn't affect that.

... BUT... that ain't working.

So go ahead and resize so that it's the shoulder that stops the cartridge going forward in the chamber, not the rim.
(Not unlike where many of us resize the belted cases like the 300WinMag)

That means:

Partial resizing to where the case will just re-enter the chamber and the bolt bolt just close w/o significant resistance.
Then measure that ersatz headspace dimension* with the 0.400" insert from this headspace comparator gauge set,
http://www.midwayusa.com/product/47...-headspace-gage-5-bushing-set-with-comparator
write it down, and use that dimension to set the FLsize die every session.


*Sorry Guffey ;):D
 
I fired five rounds again today and had another seperation, luckily outside the gun.
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You lost me- what does "outside the gun", mean?

As in, you ejected the brass- and it separated on ejection?

Not sure why no one has mentioned the other most common cause of case head separation- especially valid in the case of old milsurps- which is excessive headspace. A half-dozen reloads is nothing if not loaded excessively hot.

The backs of the locking lugs, or the bolt lug raceways in the receiver could be worn to the point where headspace has increased beyond spec.

"Oversizing" wouldn't be relative here because the brass has been sized relatively few times for this to be a factor. Bumping shoulders to the factory die settings a half dozen times or so isn't going to overwork the brass- again, provided the loads haven't been hot.

Suggest you get a no-go gauge and cease firing the gun until you can rule this out.

Disclaimer: this is not a substitute for a no-go gauge, but you can try this:
Take two layers of cellophane packing tape (usually about .002 thick) and place them over a case rim, trim tight with a razor knife.

Run the bolt- GENTLY- a few times to get a feel for the amount of resistance you encounter closing the bolt fully on an empty chamber.

It's best to remove the ejector for this- but MN ejectors often stick, and are easily bent/damaged when trying to remove them- so be careful.
Place the empty case with the tape on it into the action, and run the bolt carefully feeding the neck into the chamber. Now- gently again- start to close the bolt. It should close with the same resistance as before.

Now, remove the case- and add a third layer of tape. SAAMI spec is .066 go, .071 no-go, which equals .005. This third layer should give you about .006, exceeding that. Do the same thing- insert the cartridge, gently run the bolt.
With the same amount of force, the bolt should close about halfway- then stop. Do not force it or apply more force than before. Tape is "squishy"- it will compress unlike a correct steel gauge.

If the bolt closes easily, get a no-go gauge or field gauge to get accurate results. A field gauge will tell you only if it's safe to shoot- but you'll still end up stretching brass to the extent that they're not useful for handloaders. Suggest you get the no-go gauge instead.

If the bolt closes only halfway with the third layer- it's likely something else is amiss.

MN's generally do not suffer from excessive headspace, but I always check them. One of the first I owned had it, fixed it with a new bolthead.
 
As in, you ejected the brass- and it separated on ejection?
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The brass ejected fine. But when I went to inspect it, I saw the black ring and I was able to pull the case head off by hand without any effort.

Please remember, this was only two, out of 20 rounds, and those two have been loaded the most. I did the paperclip check on the brass that did not separate and none (that I felt) had an obvious bump.

I will try the tape thing.
 
Tip- when removing the ejector- first try to flex it away gently from the bolthead to be sure it's free. Often, they're gummed up (but still function). If it's sticking, use some brake cleaner or other solvent to free it up.

Again- be really careful. They bend VERY easily. Drive it straight down/out with a punch with the bolthead clamped in a vise if you have one.
 
Ahh yes, I knew it was coming. Headspace. Why would you risk damaging the extractor to check headspace? Actually, why would you even bother to check it in this case? The problem started with resized brass. These chambers were cut under wartime conditions, unless you have an older model. There IS a difference in the chamber size between the two. Wartime guns ran steel cased ammo and the chambers were sloppy. I have owned both and this is obvious when you fire a lot of ammo through them. I had a Finn Hex receiver that would not chamber some steel cased ammo at all. I don't consider 5 reloads bad at all using brass cases. As already stated, you can "Cheat" when you resize to extend brass life. I would look around for the company that makes the biggest brass. This helps a lot.
 
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