Let It Drop

Ballistic Basics

Excuse the mess, but the circular bump on the underside of this M&P9 slide is the plunger for the striker block.

In an earlier column, I wrote about the various mechanical safety devices used to make revolvers safe to carry with a loaded round in the chamber under the hammer.

“But, Tamara,” you say, “it’s the 21st century! I don’t carry one of those museum pieces!”

Okay, cool. Let’s talk about the mechanical gizmos used to make self-loading pistols drop safe.

Even with an inertial firing pin, however, a pistol’s drop-safety is not foolproof, since nature is always turning out more ingenious fools.

Probably the earliest of these is one that was adapted straight from revolvers: The half-cock notch. Simply put, this is an additional notch in the hammer between the fully-cocked position and the position of the hammer at rest. With a half-cock notch, if a cocked pistol is dropped with sufficient force, or at just the right angle to jar the hammer off the cocking notch, the half-cock notch will catch the hammer before it falls far enough to contact the firing pin and discharge the weapon.

The second drop safety is almost as old as the self-loading pistol: The inertial firing pin. Since early auto pistols were often carried with the hammer down on a live round, there needed to be a way to prevent them from making loud and unwanted noises if the hammer were struck a sharp blow. The inertial firing pin accomplishes this by being slightly shorter than the channel in which it rides.

Usually held to the rear by a firing pin spring, the inertial firing pin needs to be struck at full force by a moving hammer in order to fly forward far enough to ignite the primer. With the hammer fully at rest in the forward position, even smacking it a pretty good blow will not transfer the momentum needed to bust a cap.

Even with an inertial firing pin, however, a pistol’s drop-safety is not foolproof, since nature is always turning out more ingenious fools. If the pistol is dropped from a sufficient height and lands muzzle-first on a hard surface, the pin’s inertia could overcome the resistance of the firing pin return spring and let it travel far enough to ignite the primer. The height required to accomplish this varies with the pistol and the strength of the firing pin spring.

…should you drop a loaded pistol, you should just let it fall.

Thus came the newest development in drop safety for semi-auto pistols, the passive firing pin block. This is simply a plunger that prevents the firing pin (or striker, in pistols that don’t use hammers,) from moving unless the trigger is pulled or, in some designs, a grip safety is depressed. With a functioning firing pin safety, it is practically impossible for a dropped pistol to go off if it hits the ground.

This is why, should you drop a loaded pistol, you should just let it fall. The odds of it going off from impact are infinitesimal compared to the odds of you accidentally pulling the trigger when trying to catch it. Consider it an unwritten codicil to the four rules of gun safety: Never try to catch a dropped gun.

 

[ Tamara Keel has been shooting guns as a hobby since she was eighteen. She has worked in the firearms business since the early 1990s. Her pastimes include collecting old guns, writing, and being bossed around by house cats. ]

This article is featured in the following categories:

Published By USCCA

We're here to help you

Prepare and Protect Your Family

  • - Knowledge
  • - Training
  • - Trusted Legal Protection