Another good idea for a round is a acid filled .76cal ball(12 gauge is .76cal) for breaching walls and such.
Might also want an incindiary pellet(starting fires) and probably some sort of chem pellet(be it lethal or not).
Perhaps a 12 gauge proximity mine as well. That would be very useful.
00 buck is pretty much the 'industry standard' for APERS duty, but flechettes would be even better, and probably extend the range by 10 meters, to about 45 meters.
A .30 cal APFSDS penetrator would probably exceed 3000fps and have a range similar to a short barreled rifle, maybe 300 meters.
"When you're wounded and left on Afghanistan's plains,
And the women come out to cut up what remains,
Jest roll to your rifle and blow out your brains
An' go to your Gawd like a soldier."
Kipling-