Splitting shoulders in my Mosin Nagant 7.62x54R

[Smiddy]

Took out my Nagant last week with a spam can of what I believe is 149gr Russian or Bulgarian silver tip dated 1971 with "copper washed steel case." About 1/5 shots were splitting the cases at the shoulder. I see on a couple forums that this seems to be "normal" when it comes to nagants and surplus 7.62x54R ammo. It seems that the consensus is that this is due to age of the case having become brittle/hard over the years.

Im having trouble wrapping my head around that idea and think there may be more to it. If I'm not mistaken a Nagant uses the rim to "headspace". Is it more possible that the ammo is out of spec and the shoulder is unsupported aka too much space? Wouldn't that be more likely to cause so many cracks in the shoulders? Any other ideas of what might be causing this?

I've fired thousands of old surplus "rimless" 7.62x39 ammo and had none of these problems so it just seems fishy to me that lack of annealing would be the problem.


This is what mine also looked like:

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[Certaindeaf]

You could always check the headspace. If that is correct, that ammo is likely the culprit. Then you can either "fix" it, use brass ammo, throw it in the river, or just shoot it 'til something "fails".. not really recommended unless you have regenerative powers.
good luck

 

[Smiddy]

AARG, exactly what I don't want to do is buy a set of headspace gauges that cost as much as the rifle. However I concur that might be the route necessary. Then maybe pass them around to other Nagant guys in the community so they can check theirs. Some nice soft fire-formable brass would be the bees knees.

Pic illustrates what I'm thinking is the problem. Wiki regarding rimmed ammo says "Because the rimmed cartridge headspaces on the rim, the case length is of less importance than rimless cartridges." I would probable argue that in the case of bottle necked steel cased ammo the length is just as important to avoid pressure building at the neck. I'll probable have to do some measuring of the ammo.

Question...saami doesnt list it. Is to find Warsaw/NATO cartridge specs that would be considered an authority?

 

[trainsktg]

I would routinely split '54 Bulgarian HB in my rifles, but no other ammo has ever done so for me. I'd say its the ammo. In all honesty, the Mosin bolt and receiver are so excessively stong for the cartridge (the Finns are using 100+ yr old Mosin receivers in their current issue TAK sniper rifles) that I never gave it much thought.

Keith