The Firearms Blog has a post up about racking a Glock with just the inertia of the slide. I was skeptical, so I decided to do that math. I only have a Glock 19 at my disposal for measurement, but it can’t be that radically different than any other Glock. We can get a ballpark figure for how fast a Glock has to be moving for the slide to rack.
We can figure out how fast a Glock has to be traveling in order for the slide to rack when the Glock comes to a halt. We can do this through conservation of energy. The Glock 19 spring takes about 15 lb. or 67 Newtons to move the spring the 3.5cm it needs. Given that the energy of a spring is 1/2 Fx, that give us 0.5 * 67N * 0.035m or 1.17 Joules. To generate enough kinetic energy, the 350g Glock slide would have to move at 2.6 m/s. The human body is certainly capable of generating this kind of speed, but I’m a bit more skeptical one could stop the movement of the gun quickly enough. From a matter of force, it would take an acceleration (using F=ma) of 191 m/s^2, or about 19.5x the force of gravity. That sounds like a lot of acceleration, but it’s not beyond human capability.
What makes me skeptical is the fact that I can’t seem to reproduce this, but that doesn’t mean it can’t be done.