How about a minor conversion of the Lasguns?
I converted one for a figure recently:
I removed the barrel where it met the stock, cut the last bit of barrel away and attached the flash suppressor back to the stock to give it a bit more of a snub-nose profile.
You could probably modify a bit more, maybe change the ammo clip for a drum or sickle clip.
Then in game they can be used as a specialist pattern of Autogun with mass reactive rounds (counts as Boltgun)... Or an alternative pattern of Lasgun.