Do the Mossberg 500 & Maverick 88 pump shotguns have a smaller receiver in 20 ga, or are they all built on the 12 ga size receiver? Just wondered: this morning's paper had a classified ad for a nice little house gun: Mossberg 500, 20 ga, 18.5" bbl, never fired, $185. I shouldn't, but if it's a ligher slimmer shotgun, I just might!