Unless you have not had Internet service over the past few days, you have likely seen the video of a young man demonstrating a safety issue with his Winchester SXP pump-action shotgun. In the video, it is obvious that the gun is slam firing. The young man deliberately shows his finger was nowhere near the trigger, and, as the gun's action closes, the shotgun slam fires. Typically, the cause of such an unwanted discharge is a firing pin that protrudes through the front of the bolt face as the action is closed. You can read the official recall notice from Winchester Repeating Arms Co. here. Firearms are mechanical devices, and this video demonstrates mechanical safeties are no substitute for safe firearms handling. Always point the muzzle in a safe direction, always keep your finger off the trigger until you're ready to shoot, and always keep the action open and a gun unloaded until you're ready to fire.
