I've got a 12 ga. Mossberg 500 with a 24" fully rifled barrel with rifle sights. I've seen the mounts advertised that are mounted on the side of the guns reciever. I don't know about other pump shotguns, but the Mossberg pumps have alot of play where the receiver and barrel come together. I would think that you would never be able to sight in a scope with this type of mount. Seems like everytime you took a shot or layed the gun down or anything that casued the barrel to move would put the shot in a differentspot on your target at each shot.Is this the case? Thanks, Scott Woody