If you play an early era game. You can perfectly use the gunslinger class. There should be rules about certain modern weapons floating around.
You can use them as written.
If you want to use laser weapons you can take this:
Laser Pistol
Dmg (s)1d6 Dmg (m) 1d8 Crit X4 Range 40 ft. Capacity 1 Weight 3
All attacks with a laser weapon are ranged touch attacks agsinst mundane armor. If your wear special combat armor attacks are performed as normal ranged attack.
Laser weapons do fire damage
Laser weapons have the scatter quality, however you do not need to change ammunition. You can switch between the modes as a swift action
A power cell holds enough power for 50 shots.
Treat a laser weapon as a magical item. In addition to high purchase costs you might need a licence to wear a laser weapon.
Phaser weapons work similar. They cause negative energy damage.
