It might be seen as a poor mans autopistol. The diffence is stubgun is youre regular 6 shooter, where youre autopistol is a beretta or glock semi automatic.
So I think the damage is okay, since revolvers I believe is usually considered a bit more powerful. If nothing else, you can pretend to be dirty harry with youre future version of a magnum. :devil2:
Boltguns and pistols should probably be damage 4, since they are more powerful than stubguns. Thou its likely that the bolt weapons we find and can use, are of a smaller caliber than space marine bolter weaponry.
But otherwise looks good, I would probably but in a medium range modifier, but that might just be too much.