Excessive primer cup flow/FP impact diferences??

[TactAdv]

Last time I took out the '42 Daimler Mk II, we had the opportunity to fire a bunch of "original" Kynoch '50's-dated Mk VII ammo. After burning through a little over 400rds, and mostly on fullauto, I noticed that these fired cases exhibited what, to me at least, was some astounding levels of primer cup "flow" from the FP impacts.

Having had this gun for a couple years now, I have only ever fired 'current/new' mfgr Privi PPU 174gr FMJ and Wolf 174gr FMJ, along with a good quantity of my own reloads (PPU cases + CCI primers) using pulled down USGI .30cal 151gr tracer projos. So, not until this last trip have I ever fired anything resembling true, original, British sourced 'MkVII' cartridges.

That's not a large statistical sampling of primer examples I realize, but at least I can say that all the "non-Brit" ammo I have put through it so far, all the fired primer cups show only what I would characterize as a "normal" primer indentation, i.e., a strong inner dimpling of the primer cup face as would be expected (along with the "primer-lock" indent).

Then I get to these....(what I assume are Kynoch-made, cordite-loaded) '52 "Kynoch head stamp" Mk VII cartridges.....Korean War era fodder?....which I would have expected to give nothing less of a "proper example" of fired primer appearances. Trouble is the fired primer cups show a HUGE outwardly expressing, raised vertical ridge all around the FP indent. Gotta admit that the closest to that I've ever experienced was with the MkIV Oerlikon 20mm cases, but even there the rise of the upended primer cup was not so obvious. The positive relief extends about .040" above the base of the cartridge casehead.

Is any of this particular to Korean War era Kynoch service ammo?? Is this a known "thing"??

Take a gander at the pictures below. Any thoughts, musings, or other ideas gladly desired....(Sorry for the less than stellar picture clarity).
-TomH
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