Squib308 said: concur appears like an ammo concern. Probably the brass is bulging? have you inspected the winchester brass prior to vs. after firing? I experience like getting slide mounted over a centerfire pistol is about as severe as it will get, and anything that survives that will be good https://highimpactrounds.com/product/mossberg-590a1-spx-12-ga-20in-8rd/