Just had a look. I didn't keep any of the undamaged empties but these three don't look any different than unfired rounds except for the firing pin dimple.
lots of the surplus dose it. not a issue
http://www.canadiangunnutz.com/forum/showthread.php?879209-Surplus-ammo-issues-762x54
I think its because its steel cased and brass.
If the primers don't protrude then head space would not seem to be an problem. Is it only this particular type of ammo you have had problems with, or is this the only type of ammo you have tried ? It almost looks like a corroded chamber problem to me. In order for the case to be able to expand to the point where it can split, it would seem to indicate an excessively oversize chamber. Unless the primers show excessive headspace.
On the US forums some people had this with the Hungarian ammo........ brittle cases.



























