Bump stocks have been in the news ever since a Las Vegas gunman used the device to aid in unleashing more than 1,000 rounds into a crowd of innocent concert-goers Oct. 1, 2017. Several states were quick to ban bump stocks, with a federal prohibition going into effect March 26, 2019. The Trump administration ban faced judicial review but was deemed constitutional. Those who violate the bump stock ban can face 10 years in prison and a $250,000 fine.

But what is a bump stock? Perhaps the best way to explore the topic is with a quick true or false quiz:

  1. A bump stock converts a semi-automatic firearm into a fully automatic machine gun.
  2. A bump stock is (was) legal because of a loophole in the 1934 National Firearms Act that prohibited machine guns.
  3. Without a bump stock, it’s impossible to fire a semi-automatic firearm in such a rapid-fire manner.

All answers to the above questions are … false. Let’s explore what a bump stock is — and isn’t — in more detail.

Bump Fire Is a Process

To understand what a bump stock does, it’s helpful to know what bump fire is. Bump fire is a process, or maybe a result, but not a device. Bump fire involves handling and moving a semi-automatic firearm in such a way that the natural recoil pushes the gun forward against a stationary trigger finger.

Imagine holding your trigger finger in a vice so it’s perfectly rigid and still. Now push the firearm forward so the trigger compresses against your stationary finger. That’s an example of a single-shot bump-fire scenario.

Next, imagine allowing the firearm to recoil in such a way that it moves backward after firing, pulling the trigger away from your stationary finger and then pushing it forward again, repeating the process. If you can figure out how to keep just the right amount of forward pressure on the firearm while allowing it to move backward a half inch or so with each shot, then you’ve automated the process of shoving the gun against your stationary trigger finger. As the weapon moves backward, your stationary finger leaves the trigger and allows it to reset. As the gun moves forward, pressure is re-applied to the trigger. As long as you keep applying forward pressure against the gun, it will keep repeating the single-shot firing process until the magazine is empty.

So think of a bump stock as more of a process rather than a device. A bump stock is just an aid to make it easier for the user to bump fire a firearm.

Not Your Stock Stock

A black sporting rifle with ribbed foregrip, a 30-round magazine and a black plastic RW Arms Slide Fire "bump stock" clipped out over a stark white background.

The Slide Fire. (Photo used with permission from RW Arms)

A bump stock replaces the standard stock and performs two basic functions. The stock itself stays (relatively) stationary against the user’s shoulder. The stock also provides a trigger “shelf” that helps your trigger finger remain in a constant position. It’s kind of like a less painful version of the vise we discussed in the bump-fire process illustration. So far, we have a stationary stock and trigger finger. Now we need a way to allow the rest of the firearm to move back and forth.

The bump stock allows the receiver to recoil backward toward or into the fixed-position stock. That solves the problem of getting the firearm to move backward automatically and off the trigger finger. The forward pressure to repeat the process is the responsibility of the shooter.

To fire a bump-stock rifle, you use a strange modification of a Weaver-style hold. Instead of pressing the firing hand forward as with a pistol, you press the gun forward with your support hand. With constant forward pressure against the receiver, your support hand moves the rifle forward against your trigger finger and causes the weapon to fire. As long as you keep the right amount of steady forward pressure on the gun, it will recoil away from your trigger finger and then move forward again thanks to your support-hand pressure.

As you can see, a bump stock doesn’t make any modification to the firing components of a rifle. There’s no impact on the trigger or receiver internals. Nothing changes the design of the hammer or sear. All a bump stock does is make it easier for the user to create a careful balancing act between recoil and forward pressure against the rifle, thereby activating the trigger repeatedly.

Bump Stocks Aren’t a New Thing

Bump stocks aren’t a new thing. Bump fire is a process, not a device. In fact, you can bump fire a firearm using nothing more than a belt loop. No stock, no banned devices, no nothing other than your blue jeans. So, should we outlaw belt loops? Probably not, because like a bump stock, a belt loop is just a tool that aids the bump-fire process.

You can also bump fire an ordinary, unmodified semi-automatic rifle from the shoulder using nothing more than … your trigger finger. Yes, with the right hold, your body becomes a bump stock too. Remember, a bump stock is just a device that packages the bump-fire concept in a piece of plastic.

Now that you know the details, here’s the short explanation: Bump stocks make a gun fire by moving it against the trigger finger rather than moving your trigger finger against the gun. Whether you do that using a piece of plastic, a belt loop or nothing at all is up to you.

Legal Updates

On June 14, 2024, in a 6-3 ruling, the U.S. Supreme Court struck down the federal ban on bump stocks.