It happens from time to time. I have never had it happen with a shotgun, but have with rifles and especially .22 rimfires.

Good job on looking for a barrel obstruction. I would bet most of the injuries and barrel blow ups are from something like this happening and people don't check the barrel.

Out of curiousity what type of ammo was it. I have never had that great of luck with Remington ammo. Oddly enough I have really good luck with winchester. I guess any of them can have problems though. After they are made by humans like you and me. I work in a factory, screw ups are bound to happen.

Paul