When Does the Pistol Slide Start to Move?

We all know that when you're shooting most semi-automatic handguns, the slide reciprocates as part of the firing cycle. The Reader's Digest version is that after the primer is ignited and the round sent rocketing down the barrel, the slide moves to the rear in order to extract and eject the spent casing and make ready the hammer/striker. The slide then moves forward to pickup the next round from the magazine and chamber it. We're ready to go again. There are several different action-types, but that's the gist of it.

Pistol powder in particular burns very fast, because there's relatively little barrel to get the projectile up to speed before it exits. Because everything is happening so fast, many are under the impression that the round completely leaves the barrel before any slide movement occurs. And indeed, animations online are often depicted this way.

Cursory glances at high speed seem to bear this out as well. If you're watching something filmed at 600-1000 frames per second (FPS) you're not likely to see the difference. But at 10,000 FPS you may notice some slide movement before the bullet exits. If this is something you can see at 10,000 FPS, then 50,000 FPS must be even better–and that's what we're going to show you today (actually 50,924 FPS). These images were graciously provided courtesy of Sight Picture Media and Freedom Munitions.

You can see that some exhaust precedes the projectile leaving the barrel, and if you pay attention to the recoil spring in particular it's evident that the slide begins to move the moment the primer is struck. And it's not just Glocks. Here's a 1911 filmed at the same 50,000 FPS:

The 1911 has the same barrel exhaust as the Glock, but also a small plume from the rear of the chamber. How about a Beretta at 50,000 FPS?

Yes indeed, the slide starts moving before the complete exit of the projectile.

To be fair, this movement is very slight relative to the overall travel of the slide. Experts have told us a factory Glock slide may move 2-3mm before the round exits. However, any movement that takes place while the projectile is traveling down the barrel can have a tangible effect on downrange accuracy, which is often why aftermarket slides and barrels are fitted so carefully.

But really, watching guns shoot at 50,000 frames per second is just so damn enjoyable. Watch the full video here:

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