I would really hate to be stuck belowdecks where the walls, floor and ceiling is steel and having a firefight, you do not even have to be in the line of fire, just do bank shots.
Guns would not be my first choice, nice to have for abovedeck work but below decks I would rather gas them, flood them or just secure them in a watertight compartment thats secure against escape even if they use heavy caliber rifle bullets, now defending against an RPG is something else.
Trying to shoot out of a compartment would be asking to get permanently deafened, no matter what was used.
I would add to that that it is impossible to adequately express how LOUD it is when a firearm goes off inside a small steel box. :-)
"Put your hands up!"
"What?"
"Put your hands up!"
"What?"
:-)