Protruding primer: do we have a problem oomans?

[meles meles]

We're currently working our way through a mixed lot of military surplus 7.62x54R in our MN1891. Occasionally, maybe about one shot in thirty or forty, the bolt feels a little stiffer to open and whenthe brass is ejected and examined, the primer is flattened and pushed back, almost protruding above the case base. On one, the hammer strike had actually been inverted and so instead of being a dent it was now a tiny lump standing proud of the primer base.

Do we have a problem, oomans?

[Steve E]

Sounds like excessive headspace to me, or if the primer is flowing into the firing pin hole then the firing pin hole may be enlarged.
If this is not happening with all rounds only those from a particular batch, I would isolate those rounds and measure the rim thickness. The 7.62 X 54R headspaces on the rim. If the batch that is giving problems has a thinner rim thickness than the others that may be the source of the problem. Wether you continue to shoot them or not is up to you.

Steve

[meles meles]

I've looked at a pile of empty cases and it seems to be one particular type that seems to be affected. They're a slightly yellower shading than others, so presumably have a little more zinc in them than the others. It's also possible the 'good' cases are steel with a copper wash. I don't reload, so don't have any gauges et cetera to take measurements of thicknesses and so forth.