Squib308 stated: concur sounds like an ammo situation. Probably the brass is bulging? Have you ever inspected the winchester brass before vs. right after firing? Choke: choke is another dialogue than shotgun shells, but what choke you are working with ought to sync with regardless of what projectiles you're shooting. https://highimpactrounds.com/product/mossberg-590a1-spx-12-ga-20in-8rd/