Squib308 stated: concur looks like an ammo problem. Probably the brass is bulging? Have you ever inspected the winchester brass right before vs. immediately after firing? That cutout is the place the locking lug over the bolt physique locks into. In case you glance just ahead of that cutout, the https://highimpactrounds.com/product/mossberg-590a1-tactical-12-ga-20in-8rd/