Load too hot for M&Pc/357 but not for P226?

Hey all - I have loved shooting 13 grains of AA#9 with a Berrys 124 gr. FP out of my P226. It doesn't yield the screaming velocities I was expecting, but it's still a great load. I recently discovered that when I shoot the same load out of my M&Pc, I am unable to decap the brass afterwards. First things first: I messed up by not working up to this higher-end load when using it in a different pistol. Second, I assume that not being able to decap the brass, in addition to making my brass single-use only, is a clear sign that the load is over-pressure in the M&P. The P226 doesn't think twice about this load - does this seem normal?

Rather than give up my "flashbang" load in my 226, I might just find what the M&P likes and load separately for it.

Thanks.

Ah yes, I was aware of this issue with Speer brass, which lots of 357 SIG tends to be. I think you may have been one of the people that helped clarify this before. However, this issue seems independent. I'll test it again when I get home today, but I simply can't decap brass that's been fired with this load through my M&Pc. I take this as a pressure sign but I will certainly confirm and I'll also note how far it's flinging the brass to see if that corresponds.

Thanks again.

Everything you all are saying makes good sense - let me test again tonight/tomorrow and I'll post up.

Well isn't research wonderful.

Fired several rounds of 13.0/AA#9 and was able to decap them easily. So perhaps I'm more senile than I thought at 31. This does not bode well. Anyway, I may have gotten confused as to what wouldn't decap all those months ago.

BUT, I was re-reminded of this little phenomen: check out these primers.



Here's a closeup of one:



So I wondered if this, whatever this is, is a sign of overpressure, so I fired some rounds that were loaded significantly lower. I also fired one 125-gr. Gold Dot round. Here are two lower-loaded rounds with the Gold Dot case in the middle.



Well how about that. What in the world is going on? Is this weirdness consistent with overpressure? I find it hard to believe that all three of these loads would be overpressure in this pistol - even factory Gold Dot ammo. Maybe my firing pin is strange. Any other M&P owners seen this before?

Thanks in advance for your theories!

Well, doing some research has revealed that this is a common occurrence in striker-fired pistols. As this M&P is my only striker-fired pistol, that explains why I haven't seen it until now In the first pic, the leftmost primer looks pretty flattened - I'll have to see if others do that as well. I will admit that when loading these rounds, the first one seated to 1.130 when it should be 1.140, and I decided to shoot it anyway, knowing full well that OAL is extremely important in this caliber. Maybe that's the corresponding brass.

Thanks for the help fellas - looks like it was much ado about nothing.

Yeah, apparently in striker-fired pistols, the slide begins to move backwards before the firing pin comes out of the primer. As the slide moves backwards, the breech end of the barrel begins to dip, and that causes the "firing pin smudge" on the primer. Makes good sense - wonder how somebody figured that out!