I'm very new new to shotguns, so I may not even be using the correct terminology. Please bear with me. I bought a used-but-looks-new (maybe unfired) 870 in 20 gauge at a pawn shop. I'm running into a frequent problem, and I don't even want to load the gun until it is sorted out. Frequently, when working the slide, it locks firmly in place about a third of the way back. Nothing I've tried seems to get the slide working again except pushing the slide forward while banging the muzzle against the floor or a table. I figure I need to resolve this, and be certain it's resolved, before I ever load the gun. Ideas?