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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[CINDERS]

Just wondering due to the size of the Kynoch primer being somewhat larger V's the PPU's size also the copper may flow a bit more being a softer type of material than the modern PPU type cup just my best WAG.

I always like to increase my knowledge on ballistics as it is quite fascinating but would not the burn rate of the PPU powder be a lot different than the Kynoch's as the cordite I reckon was more of a detonation than a push. (having set a fair bit of it on fire from pulled rounds also burnt modern powder the same way noting the difference.)
Therefore my reasoning is the pressure wave from it is some what of a spike which generates a more intense push back causing the metal to flow more than the PPU cup the brass of the latter looks allot softer given the extractor mark on it.
Just wishing to learn........

[browningautorifle]

The center one looks correct, the others show signs of an enlarged firing pin hole...

[Bruce_in_Oz]

Copper primer cups vs. brass primer cups.

At any given pressure, copper cups WILL "flow" more than brass ones.

Only thing that matters is that they DO NOT puncture / rupture and have hyper-velocity gas-jets eating your striker and bolt face.

The BREN design was "lifted" from the Czech ZB series, mostly built for the 7.92 x 57 cartridge, which, of course, used the classic European .217" diameter, brass-cupped Berdan primer, as opposed to the very British .250" diameter COPPER cup on MK 7 .303 ammo.

Furthermore, if the "fit" of the striker tip to the face of the breech-block is not "close", then there WILL be primer "flow" as per the photos, even under "normal" conditions. This may happen in ALL centre-fire systems.

Anyone have pics of primers fired in 7.92 x 57 BRENs, or from the L4 series?

[CINDERS]

Rem 700's have a similar cratering flow so I never go by that as a pressure sign in my Rem-700 but more the shoulder radius at the primer cup edges.