I have been rethinking the sub-machine gun. As this is an alternate 1895 there is no reason it cannot exist, but it will not be as effective or reliable as even a Thompson.
So let's break the beast down.
1. Like many sub-machine guns it will use the equivalent of pistol bullets, which it carries in a stick or drum magazine. Pistol bullets do not have the penetrating power of a rifle. So its SV bonus is +2 @ 2pts.
2. However, it does throw a lot of bullets down range so it is likely the target could be hit multiple times. So its Pluck penalty is -2 @ 2pts
3. It has a longer barrel than a pistol, more like a carbine in fact. So it has a range of 15" @ 2 pts
4. Like a full size machine gun it can attack groups @ 3 pts, however it tends to be fired in bursts because it is not belt fed, so it cannot walk its fire.
Sub-machine gun: SV+2, Pluck -2, Range 18", can attack groups, Cost 9 points.