Even in combat a shotgun is highly effective due to the knockdown power. When we were on bunker duty we had pump shotguns, and OO buckshot in brass cased shells. My partner Ira hit a VC with a load and the dude died right now. I think he shot him twice - never too dead for another shot.
In the bunker we didn't worry about the capacity of the shotgun. 5 I think and a few guys carried them on patrol. Didn't seem to be a big deal about capacity there either.
Ironman is not combat nor is it home protection. It's a shooting spree!!! And for time -

I try to never confuse reality and shooting contests. The only crossover is the increased ability to handle the weapon.