As far as I can tell, Wild Gunman is the first arcade video game to feature a replica gun used against replica people. A longer demo is here. I remember the experience with much bitterness, because the light gun was not very sensitive, and even if you drew and fired in time, the hit didn’t always register.
The flyer below shows the cabinet and the different cowboys you could duel. Shooting Trainer (1975) was the sequel. The player fired at white bottles that popped up against a Wild West backdrop.
(Video via Shane MacDonald/YouTube; images via The Arcade Flyer Archive)
2 Warps to Neptune 
Classic! I love it!