Recently bought a Remington 870 Express 20 gauge. Pretty much a neophyite on shotguns. It says it can take 2 3/4" or 3" shells. I'm assuming the chamber is 3", although I can't seem to find documentation to support that. Anyway, I've read in other general shotgun discussions that it's better not to use shells smaller than the chamber. Anyone disagree? Also, I was told by the salesman I could use buckshot. Any differing opinions here? Main use: HD Many thanks!