This television show was the first time Steve McQueen worked with James Coburn. They would work together again in The Magnificent Seven (1960), Hell Is for Heroes (1962) and The Great Escape (1963).
McQueen worked hard to perfect his handling of the Mare's Leg, a distinctive and unique but ultimately impractical weapon. One of the maneuvers was the showy spin cock, which he accomplished flawlessly numerous times in the series. However, at the beginning of the final shootout, when the last two escapees come through the door, McQueen spin cocks the 1892 but fails to get the weapon all the way around in the constricted space behind the door, catching his hand in the lever. He grimaces and shakes his head - it's the perfectionist McQueen expressing, "Boy did I just screw up!" He completes the scene and it's used as-is.