I'm just back from the range, where I did a little bit of testing myself. I had about 78 hand loaded 165 gr plated bullets with 6.4gr of Power Pistol, which I fired without any issues at all. The average velocity for this batch was 949.7 fps. I had 22 rounds of hand loaded 180 gr FMJ bullets with 7.4gr of HS-6, which caused a lot of problems. I had 4 mags of 5 rds each and one mag with 2 rds. In mag 2 and 4, the slide caught about 1/4 " before battery for a few seconds then went the rest of the way. Both times, though the striker wasn't reset, so I had to pull the slide back a bit to reset the trigger. On mag 6, this same thing happened on rd 1 but not rd 2. I then fired about 50 rds of 180gr American Eagle, without any issues at all. This was odd, because last time I was at the range (last week), all I fired was this same 180gr American Eagle, and it did the same 1/4" pause before battery about 6 times out of 50 rds.

On the 180gr hand loads, I did ensure that I had a good grip on the weapon at all times. The shots were fairly accurate, as well. I didn't get a velocity reading on any of the shots this time out, but last time I took the chrony with these same loads, the avg was about 1300fps.

With the 180gr factory ammo, I got an avg velocity of 812fps.

So... I believe this goes back to my earlier complaint that neither S&W, nor third parties, do not supply any optional recoil springs for this weapon. I think that maybe the 1300fps ammo is maybe too much for the supplied spring. Granted, this is a little hot for my taste anyway. I'll probably stick with the 165gr Power Pistol loads from now on, since they performed so well. I still have a LOT of 180gr FMJ's, so I'll just back off quite a bit on the HS-6 to see if I have better luck. The fact that I didn't have any problems with the same factory ammo that I did have problems with last week sort of leaves that piece of the puzzle inconclusive.

My next task is to mimic the changes that xzhyncmade to his mags and slide stop spring. I'll report back again after that (I usually go to the range once a week).

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M&P 40c, PPQ 40, M1 Garand