This happened the other day. Lot of casings had nicks on the mouth like it was trying to do this frequently. I’ve shot similar reloads with out this happening. It’s a full size m&p 40. As my carry gun, it gets pretty dirty, never had an issue. I usually target practice with 180gr. These were 180gr plated flat points with 8gr of longshot, seated at 1.125 with a lee factory crimp. The last reloads I ran were 155gr with 9.5gr of longshot, same col, no issues. I cleaned the gun and bought some federal ammo to do testing. I just don’t understand. I’ve ran the gun dirty, ran 180gr reloads and factory ammo, ran that same powder and col, all with no issues. I’m extremely meticulous when I reload yet there were some casings landing at my feet and others going 10’. I’ll report back tomorrow with what I find out.