The Marines went with a slightly modified version of the Benelli M4 Super 90 and called it the M1014. The Army is in the early stages of replacing theirs - they’ve already got an all new design that is modular and uses a straight pull bolt called the M26 Modular Accessory Shotgun System. It can be used as an underbarrel mount on an M4/M16 or as a stand-alone equipped with a stock kit. That and a to-be-determined semiauto shotgun are to replace all the Army’s pump guns.
Dang. The M4 is $1800 from cabelas