Looking at the load times of ancient firearms, wouldn't it be better to make them an Encounter item?
For example, a pistol could be:
Wheel-lock Pistol, Level 3
Wondrous Item: 340 gold
Ranged 10
Power (Encounter • Fire): Standard Action. Make a Dexterity vs Reflex; on a hit deal 3d10 + Dexterity...