I had the same issue with a Taurus PT809. Gun shot excellently, but consistently sent spent casings back at my face and head. My M&P 9mm, Taurus PT92, and Glock 19 don't have the issue. Taurus finally replaced it, and the second gun did the same thing, just not as badly (went from around 98% of the time to around 30% of the time). Tried multiple types of ammo and had almost 1000 rounds through it. After one landed in the space between my glasses and forehead (even with a cap on, so it came straight back), I got rid of it. See if someone else has an M&P 9mm like yours and try theirs. If the same thing happens with theirs, then it might be you. If it doesn't happen, then it's probably the gun.