The last two range sessions with my MP9 have been plagued with a strange failure-to-feed malfunction. Maybe 10-12 times out of 800 rounds, the slide fails to completely return to battery. The cartridge seems to hang up just about 1/8" short of full lockup. Tapping the magazine or bumping the rear of the slide will not cause it to close, but all of the problematic cartridges chambered properly when I removed them and reinserted them into the magazine.
So far I've only fired this pistol with my handloads, 147grn. Zero JHPs over 3.x grains of Titegroup, mixed cases, Federal primers. I'm perfectly willing to accept that my handloads are the problem, but I saved a couple of bad rounds and mic'd them, and they're all fully in spec (C.O.A.L. within 5 thou of 1.100", etc.)