Squib308 explained: agree looks like an ammo problem. Probably the brass is bulging? Have you ever inspected the winchester brass in advance of vs. just after firing? Choke: choke is a different dialogue than shotgun shells, but what choke you might be applying should really sync with whatsoever projectiles you https://highimpactrounds.com/product/mossberg-590a1-tactical-12-ga-20in-8rd/