Recoil and reflexes.
A video of a petite woman shooting a S&W .500 Magnum made the rounds last week. At issue was an uncontrolled (negligent) discharge, occurring as a rapid “double tap.”
Watch the video, and you’ll see that as the gun recoils from the first round, a second round is ignited. The barrel is nearly vertical when the second shot fires, raising all sorts of concerns about its eventual landing place.
The various comments made (not just on The Firearm Blog) indicate a lack of familiarity with the forces at play.
If one observes new shooters closely, it's very common to see them release the trigger immediately after the sear breaks. This is particularly true where the reset force significantly exceeds the pull weight, as it does on most S&W revolvers in single action (especially the X-frame .500.) The strong rebound spring quickly, almost instantaneously, sends the inexperienced trigger finger back into the battery position.
As the trigger/finger reach full reset, the recoil has caused the muzzle of the gun to arc backwards toward the shooter's face. The shooter, who has not expected this level of violent reaction to the cartridge firing, finds that the hand does not have a firm enough grip on the gun. The hand muscles - all of them - instinctively tighten to maintain a grip and control the gun.
The problem, of course, is that as those muscles tighten so do those of the trigger finger, which is now sitting on a trigger that has reset and produced a gun that is in battery. The hand squeezes and the trigger is forced back, firing the gun again.
It's not a gun problem, and having a longer trigger travel or a heavier trigger as some suggest won't prevent this from happening. What would prevent it is proper instruction from a teacher who understands the whole issue, and is smart enough to do a couple of things: first, have the shooter dry fire the gun so that he/she understands what the trigger is going to do. Second, put only one round into the gun until the shooter is comfortable with the recoil/muzzle blast/trigger control.
The most important thing to take away from this is that it is a predictable, and therefore preventable, occurrence - assuming that the person in charge has the knowledge base necessary to do so. Some time back I took heat for having the temerity to suggest that a good shooting coach needs to have a passing familiarity with physiology, psychology, physics, and engineering. This incident illustrates why that opinion remains unshaken.
-=[ Grant ]=-