Squib308 stated: agree seems like an ammo concern. perhaps the brass is bulging? Have you ever inspected the winchester brass just before vs. immediately after firing? Choke: choke is a distinct discussion than shotgun shells, but what choke you happen to be working with should really sync with whichever projectiles https://highimpactrounds.com/product/mossberg-590a1-spx-12-ga-20in-8rd/