Case Head Separation in Mosin-Nagant.

Considering the case shape and the questionable integrity of the rifle, full length sizing should be applied VERY carefully.
 
consider this: If the bolt had room to move back 1/4 inch...
Click to expand...
But it does not. The separations occurring at 8 FL-resized firings would say it has "some" headspace excess -- several thousands associated with rim thickness and not the shoulder, and well within the solid brass web portion -- not something gross like a quarter inch.

Moreover, any partial resizing to set the rim back against the bolt face is nothing more than what the rifle is doing itself as it stretches the case back to the bolt -- only now it's stretching during a 55,000psi-level impact.**

So again I'd suggest setting the rim to meet the bolt as an interim measure to extend brass life.



** Thinking about it more, what is the difference between sizing to the shoulder in a rimmed case like the the 7.62x54R, and sizing to the shoulder in a belted case like the 300WinMag -- which is nothing more than a wider rimmed case?
 
Last edited:
Case head separations and a "ring" around the case 1/4" or so from the base are signs of excess headspace. I don't know why folks seem to believe that rifles firing rimmed cartridges like the 7.62x54R or .303 British just can't have excess headspace. They can, and do. And just because those cases have shoulders does not mean the cartridge headspaces on the shoulder and that all will be well if some magic adjustment is made to the sizing die.
Click to expand...

With a rimmed case, nothing else, not pressure, not case sizing, not the failure to bless the rifle, will cause head separation. If the chamber is too big, but the headspace is OK, the case simply "rolls out" forward; it might split or the shoulder move forward, but the head does not separate. With rimless cases, there are some other conditions, but they don't apply to the 7.62x54R.
Click to expand...

Thanks, Jim. Nice to know I'm not nutz...(well, maybe a little).
Always wonder why the most obvious seems to be passed over in favor of some obtuse, complicated scenario.

Anyway, MM...
How did you check the headspace, specifically? With the tape as I suggested?
If you want to borrow a no-go gauge- PM me.

It would be interesting- if you have, or have access, to another MN to try to chamber one of your fireformed cases from the rifle in question in it.
 
That is ridicules. Case head separation can and is caused by excessive full length resizeing/trimming. When I used to make rimmed case chamber reamers, I never put the rim on the reamer. I bored the rim area into the barrel and cut the rest of the chamber with the reamer. I then used a RESIZED case and a piece of cellophane between the front of the rim and the rim cut out in the barrel to check the depth of the cut. It gives a very tight chamber. It is kind of like resetting your die as others mentioned, only in reverse. Never had a problem or even signs of one and I did one in 7.62x54R and 8MMx54R. If you put a threaded adjustment on a bolt head and screwed it tight against the head of the case to fire every time, the brass would still eventually separate if you kept full length resizeing it.

Mosin-Marauder, You are not setting up your press wrong. As you get more experienced with reloading, you will see what the others are talking about with the "Case adjustment" using the die. It is an old trick to give your brass longer reloading life and that is all it is. There is nothing wrong with full length resizeing, but you have to check your fired cases to see what you can get out of them. Cases do not last forever.
 
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.
Click to expand...

Not always true. While it is often true for commercial calibers, the reason it is often true for them is the relatively "close fit" between the rifle chamber and the sizing die dimensions.

When you start looking at the chamber dimensions of certain military rifles, particularly the .303 British and 7.62x54R you find a different world.

"Proper" specs for the headspace point on these guns (where the rim fits) is something that can be checked, and is usually ok. But the REST OF THE CHAMBER can be "grossly" oversized. This is often called "generous chambers", and explained by either "sloppy wartime production" or "room to allow battlefield crud and still chamber ammo", or something like that.

Remember that the priority for military arms (AND ammo) is that cases work, ONCE. How much a fired case stretches (so long as it doesn't rupture on its first firing) doesn't matter much to the military.

You've had the headspace checked. IT's good. Fine. Now you need to look at the sizing die. Adjusted per maker's instructions, fine. It's now set to return the fired case to MINIMUM dimensions. This may not be the usual commercial cartridge "bump the shoulder back a tiny bit" it may be "move the shoulder back A LOT", because of the rifle's "generous" chamber. This relatively large amount of movement, on each FL sizing leads to early case failure.

I believe this is what you are seeing. and 8 loads from a piece of rifle brass is pretty good, even for commercial guns. Many times cases in .303s (the most famous example) don't last even 3 or 4 times, IF full length resized each time.

but mine is a 1941 rifle. It was actually designated a training rifle, due to one of the marks on the barrel shank.
Click to expand...

That might be one part of your issue. Many militaries, including the US, make guns "training rifles" because there is something about them that fails to meet the spec for a combat rifle. Not unsafe, normally, but something not good enough.
 
You bet. I never owned one, but it would be interesting to see the chamber size difference between a U.S. manufactured M-N rifle and a Soviet manufactured rifle.
 
Last edited:
That is ridicules. Case head separation can and is caused by excessive full length resizeing/trimming
Click to expand...

Absolutely agree- and I don't think anyone was disputing that.
What I had issue with, was dismissing excessive headspace off the bat as a potential cause.

FL size, the fireformed case is squeezed back to spec- and the brass that had flowed from the area of the casehead ends up at the neck- which is why trimming is necessary in the first place. There is always a gap- headspace- between the boltface and the back of the rim. Primer ignites powder, case is shoved back against the boltface, expands to fill the chamber.

Every time this happens, the brass at the casehead gets stretched, and thinner. Excessive headspace just speeds up/exacerbates this process- the more room for the brass to expand back to the boltface, the thinner it's going to get each time- until it separates.

I have three MN's that I regularly shoot, and brass life (FL sized, .002 shoulder bump) is no different than any of our modern rifles. Maybe I'm just lucky- but far as I know, the MN doesn't suffer from the oversize chamber issues that seem to be very common with the .303 Brit.
 
The OP fired the brass 8 times before he had a problem and you IMMEDIATELY think it is a headspace issue? Go back to 44 AMP's post and read that thoroughly. Then read it again.
 
So all that produced nothing. When someone displays honest ignorance, folks try to educate him. And that almost always fails because once an idea, no matter how wrong, gets entrenched, it is hard to get rid of.

So we have now been told that excess headspace is not a problem and there may not even be such a thing. So there is no need to be concerned about the rifle, only about setting the sizing die. Sure.

Jim
 
I'm sorry if I did something wrong, but honestly I'm kinda confused at this point. I went and had the headspace checked again, and it checked out. Sorry, again, If I'm impeding in some way.

Regards,

-Mo.
 
It isn't the headspace. :eek:

It's the case's rim as it fits in that headspace -- and there's too much slop :)... ergo case stretch on firing.

Either size for the shoulder (recommended still), or get brass with a thicker rim (which might not be readily available). ;) :D
 
I think some of you boys are getting a little crazy with all this. The brass is on its 8th reload, which is really not bad, and certainly on the back side of its useful life. Im lucky to get that with military brass in my M1's. Even with new commercial brass, I usually dont get much more than 10-12 loadings out of them.

I load a lot of 30-06 and .308 and all of it is FL resized, as I shoot them in a number of different guns, most of which are auto loaders. FL resizing to standard specs just keeps things simple, and really doesnt give up very much if anything in the accuracy department, except maybe in one or two certain guns.

It also eliminates the inevitable "mix up" and aggravation of dealing with neck sized or gun specific ammo in the wrong gun.
 
Mo:

Scrap the loads you have. They're not safe.

Go buy some Wolf Gold. It's PPU.

Fire them, and clean and trim the cases.

Back the sizing die out so that it only sizes the neck. This is what I do. The cartridge will headspace on both the shoulder and the rim this way.

I do this and get 10 loads out of them, each. I could get more but I also get skittish and trash them just in case. I do check for incipient case head separation with a sharpened and bent brass rod.

If you keep shooting your current loads, odds are better than even that you'll get hurt.

Regards,

Josh
 
Mo,

Just the ones in any cases that might be bad. I wouldn't use anything FLR more than three or five times.

Check the rest each reload, man. The ones you know to be good, check 'em anyway.

Crush the rest after you pull them down.

Josh
 
I'm sorry if I did something wrong, but honestly I'm kinda confused at this point.
Click to expand...

As far as I can see, you are doing things right. Sorry for the confusion, but you get that with different people explain things each in their own way.

headspace, of the rifle, of the cartridge, on the rim, on the shoulder, how to set the FL die for maximum case life, all have been mentioned, and I can see how it can get confusing. (forgive me if you already understand this)

7.62x54R headspaces on the case rim. Properly, in this case, headspace refers to the space in the rifle where the case rim fits, and the fit of the case in this space.

there is normally a tiny amount of clearance between the case (rim, in this case) and the boltface. When this clearance is too much, the term is excessive headspace.

You've had that checked, and its good. SO, your issue is NOT headspace, in the proper use of the term.

Your issue is how much the brass stretches on firing, until it is stopped, by the boltface in one direction, and the chamber shoulder in the other, COMBINED with how much your sizing die is "squeezing the case back down".

Because of this, your brass has reached the end of its life after 8 FL sizings. TO extend your case life (with the same load -powder amt & bullet), either a custom FL die made to match your rifle's chamber, OR backing off the standard FL die to neck size only are your main options.

Or just continue on as you have been, checking for signs of head separation, and keeping track of how many times each BATCH of cases has been FL sized.

If you are getting SOME cases fail on their 9th firing, but not all, then the 8th reloading cycle is the last straw, and in the future, you should toss the cases after the 7th time (keeping a close eye on them, checking them, because some might fail earlier than others.

Hope this helps.
 
Headspace, chamber dimensions, full-length resizing, whatever...drop back a couple of grains. Nothing you shoot will know the difference.
 
If there is a headspace dimension disparity between the rifle and cartridge, dropping the charge only a few grains will have no significant effect on case stretch.

Now if you want to drop-a-few AND oil the cartridge case..... ;)


.
 
Last edited:
You must log in or register to reply here.
Back
Top