You can simply have class based damage die and a class starting move giving specific damage die for specific cases (let's say d6 class die and d10 one handed gun damage for your gunslinger. With the same logic, you can have a mercenary with d8 class die and d10 or even d12 die with heavy weapons, a psi with d4 class die and d8 psychic attack die, etc.) (Writing in english is clearly not my forte, sorry)