I own one of these hand cannons (in 460SW). I've let only a handful of people shoot it. And I always start them with 45Colt, and then let them shoot 460SW. But never thought this could be possible since the trigger pull is long and quite hefty! Youtube videos: .50 Caliber Smith & Wesson 500 Magnum Revolver - Double Fire? - YouTube FULL AUTO 500 S&W - YouTube Double Tapping on a 500 magnum. - YouTube My hypothesis is three factors combine: * inexperienced shooter with poor handgun control, * shooting in single action with a * very high recoil energy handgun Shooters are barely exerting any force to squeeze the trigger. The poor control leads to letting go of the trigger and allowing it to reset, which leads to inadvertently pulling the trigger again while trying not to let go of the gun.