I finally got to put my suppressor on my pistol and take it to the range the other day. I had some 115gr and 147gr FMJ. Everything fed and fired just fine, but every time I fired the last round of 115gr the magazine partially ejected from the magwell. Not much at all, but enough that the mag was completely out of the mag release. Of course the slide did not lock back after the last round. This did not happen at all with the 147gr, but occured at the end of every mag loaded with 115gr. The slide did lock back after the last round every time I shot 147gr.

The pistol/suppressor setup is:

First Gen M&P9 with a factory mag release (changed from blk to FDE about a year ago but I don't think there was a design change) and a Second Gen factory M&P threaded barrel

Two different factory M&P9 17 round mags (for some reason I never loaded them to capacity that day, only 5-10 rounds per mag each time)

Innovative Arms 9mm LEX suppressor threaded 1/2x28

Ammo used: 115gr Federal FMJ / 147gr Freedom Munitions FMJ ("new" not remanufactured according to their website)

Pistol has a TLR-1 on it, not that it should matter.

Pistol also has the mag disconect feature.

I was figuring there was more backpressure caused by the 115gr rounds, and that was somehow causing the mag to be pushed or "blown" (for lack of a better term) out of the mag release.

Anyone have any thoughts?