cool.
It is about the right overall length but I don't think so. The forarms are vastly different. It's hard to tell from the photo if the captains gun is a smoothbore or a subgun. As I look at the photo, the captains gun may have a barrel shroud and a vertical magazine but that may be due to light reflection and what looks like it might be a magazine near his left knee is actually something else. I wonder if there is any chance that it's a civilian shotgun that he cut down?