what is that?
That is a Kel Tec KSG
https://www.keltecweapons.com/shotguns/ksg
My son got one when he came back from Bagram.
Click on “THESE” in my post. They are 12 gauge mini shells by Aguila. Some pumps can’t handle them without jamming. Looks like the Mossberg 500 (and probably others) need an adapter to handle them, but lighter recoil and higher mag capacity are big pluses.