Quote:
Originally Posted by MichiganScott
Looks like the OP is new to the world of M&P semi-autos. The marks on those primers are caused by the relief cut in the breach face. It's part of the design of the M&P's and has nothing to do with pressure.
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Actually, this is my 2nd M&P, the 1st going to my youngest son a couple of years ago, and I am aware of the facts you mention.
Please note in my original post that I didn't say those marks were anything other than common to the cases shown.
However they do, in fact, have something to do with pressure, that being what caused the metal to flow into the breech face relief cut, 'though not necessarily excess pressure.