As it sits presently, all of the SMG's except for the tommy gun are terrible. If you want the game to be realistic that's just fine as AR's actually DO completely dominate SMG's in every way except for size, but this is NewZ not a simulator game.
The purpose of SMG's should be to dominate the ranges in between shotguns and AR's. How do we do that? We tweak our damage output and effective range until smg's are very powerful at close range, and we nerf the effective range so that AR's match or beat the SMG's beyond 15-20 yards or so.
Lets look at the Damage per second on a few guns.
mp5 - 231
p90 - 231
Red stalker - 231
Tommy Gun - 245
m4a1 - 250
Mini-Uzi - 264
Famas - 279
QBZ - 280
AK-74u - 280
AK47 - 282
Masada - 284
PKM - 346
Shotgun - 203 (instant, not really per second)
Who on earth would accept damage output that is, at best, on par with mid-tier AR's when they can just take an AR and get 2-5x the effective range with the same damage??
After writing all of this out, it is my conclusion that for a player to even CONSIDER running an SMG, the absolute minimum damage output is about 280 per second. A number in the low 300's would make more sense, combined with spread numbers between 4.5 and 7, and decay numbers between 10 and 20.
Here's what a proper smg would look like (i am thinking of the UZI here):
Damage - 19.5 (309 per second)
fire rate - 950
spread - 5.5
decay - 11
this weapon would be incredibly deadly out to about 15 yards, but almost useless as you get out to 20 yards. In order for a gun to have DPS around 300, it MUST be very weak in some other dimension, in this case range. That's also important because if an smg had such high DPS and was also good out to, say, 40 yards, then AR's would start to become obsolete. This was sort of the issue that Tommy guns had pre-nerf, with a decay of 40 and a decent spread they were competing with the best AR's out to 45 yards.
For open world you also have to consider that snipers beat AR's really badly beyond about 50 yards, while on open world / AR only servers red stalkers can run effectivly out to 100-125 yards. If SMG's have huge damage numbers, and are effective out to 40-50 yards, then AR's become obsolete in open world. That's not good! This is another reason I think SMG's must be kept as 15-25 yard guns MAX. Decay and spread must be nerfed if damage output is to be increased!!!
The main problem is that the effective range of shotguns are limited primarily by spread, not decay. Spread on shotguns needs to go WAYY down, and decay also needs to go down to 2-5. After this change damage may need to be lowed from 203 per shot down to about 175. This doesn't necessarily give shotguns any more effective range AT ALL, what it does is make shotguns more reliable, instead of up to chance with the pellet spread.
Some of the shutguns should have slightly different stats, with the double barrel perhaps having high spread and high damage, and the mossberg maybe having low spread but also barely enough damage to one shot.