my guess is that once people either bought up all the ARs, they went towards "tactical" shotguns or, in some states like Colorado, where even pump guns with 8-rdn tubes are being targeted, thier was a rush, though less publicized, on pump-shotguns.
That being said, if you can find one, can't go wrong with the 590 series. Love mine.
that is, if you don't loose the bolt.
