Squib308 said: agree appears like an ammo issue. perhaps the brass is bulging? Have you ever inspected the winchester brass before vs. soon after firing? That cutout is in which the locking lug on the bolt physique locks into. Should you look just ahead of that cutout, the extention is https://highimpactrounds.com/product/mossberg-590a1-spx-12-ga-20in-8rd/