Shotguns are largely unreliable. The only time to use them are A: if it's the first weapon you have B: the only CQC weapon available (no SMG's) or C: you have a choke. A choke makes most of the shotguns go from a 50% chance of one shotting with a body-shot to something like 85%. The S686 with a choke has some extreme range, but only two shots. The pump shotgun with a choke is great for people rushing your house. The S12k is mostly bad except with a compensator and extended quickdraw. It'll never have the tightness of a choked rifle, but you can get 7 shells off in about 3 seconds which is more than enough for one person if you control the spread.
Overall for close quarters I'd never, ever pick up a shotgun if ANY smg is available. And then I usually dump an SMG for a red dot SCAR as my close quarters. For SMG's the Ump is a very practical weapon and I used to use it exclusively until more recently. I'd say for SMG's it's UMP (try burst with a red dot if you don't have an AR as well) > Vector (only with extended mag) > Tommy Gun (honestly haven't used it much) > Uzi (stock and compensator help immensely). The Uzi isn't bad, but iron sight only and it takes 7ish bullets to kill some one with a 2 vest in the body and it only has a clip of 35 with extended. The real key to SMG's is controlling the recoil into their face. Nipples to nose will kill anyone instantly as no matter WHAT the gun, 3 headshots will kill them. Even with a 3 helmet. 3 Uzi bullets will kill some one. I think it's less for T1 helmets and T2 as well.
Overall shotguns do suck, but they can come in handy if you get a nice line up on the shot with a choke on. I have a clip of me killing a guy with a shotgun blast instantly. I went to loot and his 1 helmet and 3 vest were untouched. Not sure if that's the shotgun's problem or the 3 Vests are bugged as people are claiming now.
