More than likely. He was evidently pretty fond of the scatter gun, as evidenced by the following accounts:
1880, Mexico:
Slaughter, two black hands named John Swain and Old Bat, and several other cowboys had gone into Mexico to retrieve stolen stock. As they drove the stock back to the ranch, bandidos appeared, and Slaughter's Mexican vaqueros fled into the brush. But John and the two black cowhands drove the stock into a box canyon and readied their shotguns for action. The bandidos charged into the canyon, into the face of those shotguns. John and the two cowboy's quickly drove the bandidos away.
1887, Fairbank, Arizona:
John and Deputies Burt Alvord and Doc Hall tracked Gerónimo Baltiérrez, a murderer and bandit, to Fairbank. Baltiérrez and his señorita were in a tent about one-half mile from town, the three lawmen surrounded the tent and ordered the outlaw to come out. The outlaw slit the side of the tent and ran to a nearby fence, where Slaughter killed him with two blast from his shotgun.
June 7, 1888, Cochise County, Arizona:
John, Alvord, and two Mexicans had trailed a group of bandits to their camp in the Whetstone Mountains. At dawn John, shotgun in hand, ordered the sleeping outlaws to surrender. John then opened fire, wounding one of the fugitives. The bandit leader, Guadalupe Robles, jumped to his feet with his pistol in hand. John shot him dead. Another outlaw named Manuel sprinted out of camp, John shouted, "Burt, there is another son-of-a-____. Shoot him!" Not waiting for Burt, John shot the fleeing man and hit him. Then he ordered the rest of his posse to chase after him and kill him. The man somehow escaped.