Les Jones

Guns > Study of Unintentional Discharges

This is a fascinating study of unintentional discharges in a controlled setting. A researcher gave officers a SIG modified with a pressure-recording trigger and had them go through a course of fire to see if they touched the trigger, and if so how much pressure they applied.

In his first study, 33 male and 13 female officers of different ranks and years of service, were sent into a room to arrest a "suspect" and to "act in a way they thought appropriate" while doing so. The officers were armed with a SIG-Sauer P226 that was rigged with force sensors on the trigger and grip. All the officers were instructed that if they drew the gun during the exercise, they were to keep their finger off the trigger unless they had made the decision to shoot, per their training and department regs.

As the role-play evolved, 34 of the 46 officers drew the gun and one officer actually fired, intentionally. Of the 33 others who drew, all insisted that they had followed instructions to keep their finger outside the trigger guard, because they'd not made a decision to shoot.

Seven of the 33 -- more than 20 percent -- had, in fact, touched the trigger hard enough to activate the sensor. Even the officer who eventually fired his weapon "not only touched the trigger twice before actually firing and once again afterwards, but also had his finger on it long before actually firing," Heim notes. Yet he too maintained he'd kept his finger well clear of the trigger until the very split-second before he fired.

In a second series of experiments Heim explored how various body movements might affect an officer who has his or her finger on the trigger but does not have an immediate intention to shoot. Specifically, would certain movements cause an officer to involuntarily increase pressure on the trigger enough to unintentionally discharge a round?

Heim ran 25 participants (13 female and 12 male, average age 25, all armed with the sensor-equipped SIG) through repetitions of 13 vigorous movements common to police work while their index finger was on the trigger.

In about 6 per cent of cases, enough trigger pressure was registered to have fired the pistol had it been uncocked (that is, mechanically set for an initial double-action trigger pull). In about 20 per cent of cases, the pressure was sufficient to have fired the gun had it been cocked (as with secondary rounds). The gun used had a 12-pound double-action trigger pull and a 5-pound pull, single-action.

The motions that caused the greatest contraction of the trigger finger--and thus the greatest force exerted on the trigger--were all jumping motions, whether with both legs or a single leg on either side of the body. The next greatest contracting force was caused by an abrupt loss of balance. Next were single-leg kicks (especially using the gun-side leg).

For me this confirms what I've thought for some time. Learning rule three (keep your finger outside of the trigger guard until you're ready to shoot) is necessary, but not always sufficient. You can say "just keep your boogerhook off the bangswitch" but people will sometimes squeeze the trigger anyway, for reasons detailed later in the article. Some guns - particularly those with thumb safeties and heavier triggers and trigger takeups - are somewhat less likely to discharge in those circumstances, but even heavy DA triggers aren't a cure-all.