On February 18, 1878, members of the Jesse Evans Gang shot and killed John Tunstall, which sparked the Lincoln County War. The Lincoln County Regulators, led by Dick Brewer, were formed to bring to justice those involved in the Tunstall murder, and several were killed over the following months, to include the Regulator leader Dick Brewer, and with Buckshot Roberts, William Morton and Frank Baker being killed by the Regulators, and later Sheriff Brady himself along with Deputy George W. Hindman. Peppin was present during the Sheriff Brady shootout, but was not wounded. Following Brady's death, John Copeland was appointed to the office of sheriff, but was dismissed shortly thereafter due to his refusing to take the side of the Murphy-Dolan faction, and he was replaced by Peppin, whose loyalties were with Murphy-Dolan, and with his weak demeanor he was easily influenced by that faction. Peppin deputized members of the Murphy-Dolan faction, to include Evans, a main suspect in the Tunstall murder. He then led a campaign against the Regulators, resulting in the death of Regulator Frank McNabb and with Regulator Ab Saunders being seriously wounded during the gunfight at the Fritz Ranch. Peppin then led a posse into Lincoln on July 15, 1878, to clash with the rest of the Regulators, assembled by Alex McSween. In what would become known as the Battle of Lincoln, Peppin and his posse well outnumbered the besieged Regulators, and received assistance from the US Cavalry under the command of ColonelNathan Dudley. That battle ended in a draw. McSween and his business partner Harvey Morris, along with Regulator Tom Cullin were killed, as were Peppin's men, "Dutch Charlie" Kruling, Bob Beckwith, and Charlie Crawford. Other Regulators escaped, and although the tensions continued for some time afterward, for all practical purposes the Lincoln County War ended there.
Aftermath
Peppin lived in fear following the range wars end, resigning as sheriff immediately afterward, and begging for sanctuary at Fort Stanton, where for a time he worked as a butcher. He also worked as a butcher for rancher Pat Coghlan for a time during this period, before returning to work as a mason. He testified in the court of inquiry on behalf of Colonel Nathan Dudley, and later testified against Billy the Kid in the killing of Sheriff Brady. Peppin lived out the remainder of his life in solitude, dying in 1904.