Eugene Cunningham 
Triggernometry 

This widely regarded classic represents a volume of biographies of numerous master gunfighters, including such notables as John Wesley Hardin, Billy the Kid, Dallas Stoudenmire, Sam Bass, Wild Bill Hickok, Butch Cassidy, and Tom Horn. Himself a Westerner familiar with the feel of pistol and rifle, Cunningham knew firsthand several of the Texas gunfighters featured in his book, the product of more than 35 years of research, interviews, and writing.