From The Feud: The Hatfields and McCoys: The True Story, by Dean King (Little, Brown, 2013), Kindle pp. 209-210:
The two sides fired on each other for, by one estimate, more than two hours…. After the initial strikes, the outnumbered Hatfields took the worst of it. Already missing fingers, Mitchell was shot in the side. Indian was drilled in the thigh. A man named Lee White was hit three times.
Just who had the better arms in the battle is a matter of dispute as each side subsequently tried to downplay their weaponry. “The Hatfields fought with the best rifles that money could procure, heavy caliber Colts and Winchester rifles,” wrote journalist Charles Mutzenberg. “The Kentuckians were armed less perfectly, about half of them using rifles and shotguns of the old pattern.” According to him, only Bad Frank [McCoy] and two others had repeating rifles, which accounted for the Kentuckians’ “heavy losses in horses and wounded men.”
Cap’s son Coleman disagreed, saying: “Anse, Cap, and a few other of the Hatfields were armed with .45 caliber one-shot cartridge Spencer rifles. The remainder of the Hatfield side had only cap-lock squirrel rifles and such other muzzle-loading weapons as had been handed down from the Civil War.” He claimed that the McCoys used Winchester repeating rifles bought from the riverboats that plied the Levisa Fork to Pikeville.
In either case, the relative lack of sophisticated weaponry was indicative of just how slow “progress” was in coming to the region, despite its increased economic well-being. It was certainly a factor in the number of casualties suffered in the feud. Had they had better and more accurate guns, more people would have died.
Firearms had evolved rapidly since the war. The original Winchester—the Model 1866 lever-action repeating rifle (like others, named for its introductory year), which fired multiple shots without requiring reloading—had changed gunfighting forever. The highly portable 1873 carbine with its short, twenty-inch barrel was so widely disseminated (to the tune of 720,000) that it has been called the gun that won the West. Colt adapted its Peacemaker revolver to fire the same ammunition, allowing those armed with both to carry only one type of cartridge. And everyone from buffalo hunters, Texas Rangers, and Canadian Mounted Police to Geronimo carried the ’76 Winchester, which celebrated America’s centennial with more potent firepower.