The Specter 1882 short barreled variant in 12 gauge from Hunt: Showdown! Based on the very first pump action shotgun, the Spencer 1882. This unusual shotgun takes a little getting used to, since you cannot load shells with the action closed.
If you want to fully load this shotgun, you need to open the action, load shells until full, close the action which puts a shell in the carrier, open the action with the bolt release, load one more shell, then close the action. Loading a shell before it's empty will eject an unfired shell, and with practice you can catch that unfired shell and feed it back in.