Squib308 reported: agree sounds like an ammo difficulty. Probably the brass is bulging? have you inspected the winchester brass in advance of vs. right after firing? MGL Chapter 140 stated: “Big potential weapon”, any firearm, rifle or shotgun: (i) that is semiautomatic with a fixed big potential feeding machine; (ii) https://highimpactrounds.com/product/mossberg-590a1-tactical-12-ga-20in-8rd/