I have an 870 supermag and I'm looking to put a red dot on it for turkey hunting. My question is regarding mounts for these. I have seen the B-square type mounts but would rather have something that mounted to the barrel instead of the receiver since I have another barrel for waterfowl hunting. That way I don't have to remove the mount every time I change barrels. Anyone know if there is a mount that I can put on the rib of the barell?