Case Head Separation in Mosin-Nagant.

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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I disagree.
First- I don't see where the OP posted the date of his barrel- so what makes you assume it was "wartime"- and therefore "sloppy"?

I have never seen evidence to support your assumption. Yes- I've seen plenty of sloppy cosmetic machining on wartime- fabricated rifles, but that's cosmetic. Why would they care about running the tool bit down the barrel one last time to remove tool marks? Entirely different to say chambers weren't cut correctly. I've put thousands of reloads downrange with my MN's- with S&B and Prvi brass- and never had issues with any of them as far as brass goes.

Everyone has an opinion, and the internet is full of them- including yours and mine. My point is, case head separation can have multiple causes, or combinations of them. I've been told on other forums that checking headspace on milsurps is "overrated". So be it. I'm not going to fire a 100 year old military rifle without first doing at least them most rudimentary, cheap, and fast test that can be done.

Rather than advise continuing to shoot a potentially dangerous rifle, I would tell any of my customers as an FFL to check the headspace before continuing to shoot the weapon.
 
I used to have it in my sig, but mine is a 1941 rifle. It was actually designated a training rifle, due to one of the marks on the barrel shank.
 
You have documented a relatively well known characteristic of bottle necked, rimmed cartridges.

My suggestion is to send three fired cases to the folks at C&H Tool and Die and have them make you a custom sizer for your chamber. Since the cartridge headspaces on the rim, the shoulder often blows forward in chambers made under the duress of a war time production. You set the shoulder back upon full length resizing, and voila. It blows forward again, stretching at the fire ring.

If you try to partially resize your cases, often the body of the case won't be squished down enough.

So a custom die is a good investment, only costs maybe $50 or so.

FWIW. Same holds true on 303 Enfields.
 
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Different chamber sizes is not an "Assumption". This is a common occurrence with military rifles. The rifle that I was describing as "Pre-War" was a Hex receiver with all matching numbers. The first commercial hunting loads that came in from Russia were copper washed steel/ with soft point bullets. The rims were so coarse that the burrs on the rim actually gouged the face of the barrel where the rim seats. Some would not even allow the bolt to close. I had Type I Japanese Carcanos that you had to force the bolt down on WWII Japanese ammo because the chambers were so tight. The OP is using aftermarket brass in a war production gun. There is a difference. What the OP is describing is as others have posted: A common occurrence with rimmed cases. I have noticed that headspace is becoming more and more of a problem since the internet came to be.

Moisin Maurauder, Take UNFIRED Winchester brass and mic it down by the head, and then do the same to other brand UNFIRED cases you have. You will probably see quite a difference in size. I have always found Winchester brass to be on the low side. Makes a heck of a difference when full length resizing.
 
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I'm just going to keep going about my life. I see no real reason to stop shooting it/reloading for it. 8 reloads is more than my moneys worth. I've checked my gun twice over and had the headspace checked (again) and it's still gtg. Thanks again for all your help!

I plan to start checking my brass on the inside with a small pick to check to see if there is the ring in the inside after several reloads.

Also, I don't have any unfired winchester brass, I used it all. But the Prvi brass chambers fine And ejects fine.
Regards,

-Mo.
 
I see no real reason to stop shooting it/reloading ....
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Case head separations are serious business.
Start partial resizing to fit the chamber, or wear triple thick safety glasses,
...and expect some forehead/cheek tattooing sooner or later.
 
While they are/can be serious, they are inevitable, no matter what you shoot, if you shoot the brass to failure. 8 reloads is approaching old age for most.

Keeping track of things, following proper reloading techniques, and looking for the problem as the brass is used, usually allows you to scrap the brass before it becomes an issue or danger.

One other thing I wont do, is use rifle brass I dont know the history of. I dont scrounge rifle brass at the range, buy "once fired" stuff you see advertised, as it can be difficult to be sure it really is, and only use either factory brass Ive fired, or new, factory cases meant for reloading.
 
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.

Jim
 
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.
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Headspace had been checked.

Twice.
 
Headspace had been checked.
Twice.
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Have you checked the headspace/chamber recess against the case rim thickness?

I had a 45-3¼ that began getting head separations on a falling block at black powder pressures. Turned out the rim thickness was too thin. It didn't matter that the "headspace" was right. The case headspace dimension was wrong for that rifle.

Changed brass manufacturer and the problem went away.

What is the chamber recess/headspace ?
What is the case rim thickness ?
What is the difference between the two ?

NOW... make that rim irrelevant: Partial size for the shoulder dimension, not the rim.
 
7-8 firings is pretty good out of a war production gun using a rimmed cartridge. Talk about the proverbial mountain out of the molehill.
 
Mosin-Marauder

this load shot well the first time, so I figured I would load a bit more and change to match primers.
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I have no idea what prompted it to do this, but I am looking for any advice.
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I didn't see anybody else mention this, so I figured that I would bring it up. It is advised that whenever switching primers, the initial loading should be downloaded by 10% and worked up again. From your OP, it sounds like you swapped primers and used the same powder load as before.

I read an interesting article in the most recent Hogdon reloading annual magazine, where loads were identical and the only change was the primer. Standard, magnum, match of different manufacturers were interchanged, and the pressure difference was a real eye opener. If I recall, some changed by 6000 psi or more.

Case head separation is usually caused by brass reaching the end of it's useful life. The useful life can be significantly shortened if the casing is repetitively FL resized more than necessary, ie overworking the brass.
 
You are absolutely correct. The Frankford Arsenal did studies on point of impact and what affects it years ago. Changing primers had the most affect. Changing bullet style, brass, and even going up and down a few grains had less affect on point of impact than the primers did.
However, in this case it appears to be simply a matter of inexperience with reloading. I know people that don't get 8 loads out of 30-06 or .270 brass.
 
I don't really see how I'm resizing wrong. I set up the die just like every manufacturer says to do, I lube cases correctly etc. I most likely wont be using these primers again in this cartridge, though.

Thanks all for your help!
 
Before you go away mad, let's look at the basics. When a rifle is fired, the pressure pushes out from the inside of the case in all directions. The thin front part of the case is pushed out against the chamber walls, keeping the front of the case from moving. The pressure also pushes back against the inside rear of the case. But that part of the case (the head) is solid and is not expanded like the front is. So the case head pushes back against the bolt face. Normally, the bolt cannot move very much, and all is well.

But if the bolt head can move, the case head can push it back. With the front of the case immobile and the rear moving back, the case is stretched at the point where the solid head thins down. If the case is stretched enough, the head separates from the case.

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.

(There is one point I will mention in regard to the .303 British. Under extreme pressure, the early MLM/MLE/SMLE action can actually bend, allowing the bolt head to move and create a temporary excess headspace condition. When the pressure drops, the action can spring back, and all or most of the excess headspace will go away. But that does not apply to the M-N, which has its locking lugs on the front of the bolt.)

Jim
 
Having difficult extractions and head separations indicates bad headspace. Check it. Requires proper headspace gauges that in the case of 7.62 x 54R, most smithies will not have. Rent 'em from www.reamerrentals.com or 4-dproducts.com. Cheap thing to do. Runs about $7 for 3 days from the former.
There is no changing how a rifle is headspaced by doing anything to the case. Headspace has nothing to do with the case.
"...load a bit more..." How much more? 51.2 is very close to minimum, but you should not just add more powder. You should load 5 of each load starting at 51.0 and going up by half a grain to the max of 55.0(C), then go shooting off a solid bench at 100 yards for group only.
 
"Set the die to only partially resize so that the case is headspacing on the shoulder... not the rim."

Sorry, mehavey, but DON'T. A rimmed case is supposed to headspace on the rim and seting the die so it stops on the shoulder can make things worse if the rifle has excess headspace.

If you don't think so, consider this: If the bolt had room to move back 1/4 inch, but the shoulder of the round was moved forward 1/4 inch, your case would fit perfectly. But the unsupported case head would burst and leave you holding a handful of hot gas and pieces of case and action.

Jim
 
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