This may be a retarded question, but I'm new to shotguns. I bought a regular Remington 870 express synthetic. Not the magnum version. I know I can only use 2 3/4 and 3" shells. I've seen 3" magnum shells...am I able to use these? I assume the answer is no, but I'm not positive. I can't seem to find buckshot anywhere around here unless it's magnum 3".