A bump stock is a firearm accessory that uses the recoil of a semi-automatic rifle to make it fire faster, mimicking the rate of fire of a fully automatic weapon.

The device attaches between the rifle's stock and the receiver. When you fire, the gun recoils backward into your shoulder, and the bump stock's internal spring pushes the gun forward again. Your finger stays in contact with the trigger, so the gun fires again as it moves forward. This cycle repeats as long as you hold down the trigger, producing rapid fire without the shooter having to pull the trigger multiple times per second.

Bump stocks became widely known after the 2017 Las Vegas shooting, when it was discovered the shooter had used them. The devices had been legal under federal law for years before that, sold openly by gun retailers. In 2019, the Trump administration banned them through the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), classifying them as machine guns under the National Firearms Act. Possession of a bump stock is now a federal crime.

Key Takeaways

  • A bump stock uses a gun's recoil to cycle the trigger repeatedly, allowing a semi-automatic rifle to fire at rates similar to a fully automatic weapon.
  • The device was legal and commercially available in the United States from the early 2000s until 2019.
  • The federal ban on bump stocks took effect in March 2019, making possession illegal nationwide.
  • Violating the bump stock ban can result in federal criminal charges, including felony charges.

How the Mechanism Works

A bump stock has a hollow stock that slides over the rifle's original stock. Inside is a spring and a support arm. When you fire the rifle, the recoil pushes the gun backward into your shoulder. The spring then pushes the gun forward again. Because your finger is resting against the trigger and the trigger guard, the forward motion of the gun causes the trigger to move backward relative to your finger, firing the gun again.

The cycle repeats as long as you hold down the trigger and maintain forward pressure with your non-trigger hand. The rate of fire depends on the gun's recoil strength and the spring tension in the bump stock, but it typically produces 400 to 800 rounds per minute — comparable to military automatic weapons.

Different bump stock designs work slightly differently. Some use a sliding stock, others use a hinged design. All operate on the same basic principle: using recoil to reset the trigger without the shooter having to release and re-press it.

Legal Status and the 2019 Ban

Bump stocks were first manufactured and sold in the United States around 2010. The ATF initially ruled they were legal because they did not convert a semi-automatic rifle into a fully automatic weapon in the technical sense — the gun still fired once per trigger pull. However, the rapid cycling of the trigger created the practical effect of automatic fire.

After the Las Vegas shooting in October 2017, where a gunman used bump stocks to fire into a crowd and kill 60 people, public and political pressure mounted to ban the devices. In December 2018, the ATF reversed its position and issued a new rule classifying bump stocks as machine guns under the National Firearms Act. The ban became effective on March 26, 2019.

Under the ban, possession, manufacture, transfer, or importation of a bump stock is a federal felony. The ATF ordered owners to destroy their devices or turn them in. Violating the ban can result in up to 10 years in federal prison and fines up to $250,000.

State-Level Variations

While the federal ban applies nationwide, some states had already banned bump stocks before the federal rule took effect. California, Florida, New York, and Washington were among the first. Other states passed their own bans after the federal action.

A few states have no additional state-level restrictions beyond the federal ban. However, because the federal ban is the floor, bump stocks are illegal everywhere in the United States regardless of state law. State penalties may be more or less severe than federal penalties, but the federal prohibition applies in all cases.

Why the Ban Happened

The primary reason for the ban was that bump stocks allowed semi-automatic rifles to fire at rates that made them functionally equivalent to automatic weapons, which have been heavily restricted since 1986. The devices created a loophole: a gun that was legal to own could be modified to fire like an illegal automatic weapon.

Policymakers and law enforcement argued that the practical effect — rapid fire capable of killing many people in seconds — was what mattered, not the technical mechanism. The ATF's reversal reflected this reasoning: if a device allows a semi-automatic gun to fire at automatic rates, it should be treated as an automatic weapon under existing law.

Frequently Asked Questions

Are bump stocks still sold anywhere in the United States?

No. The federal ban prohibits manufacture, sale, transfer, and possession. Any bump stock sold after March 26, 2019, is illegal. Retailers cannot sell them, and individuals cannot legally own them. Attempting to purchase one online or in person is a federal crime.

What should I do if I own a bump stock?

You must destroy it or surrender it to law enforcement. The ATF provided a amnesty period for owners to comply without prosecution, but that period has ended. Continuing to possess one now exposes you to federal criminal charges. Contact your local ATF office or police department for guidance on how to surrender or destroy it legally.

Can someone be prosecuted for owning a bump stock before the ban?

Prosecution for pre-ban possession is unlikely because the devices were legal when purchased. However, anyone who possessed one after the ban took effect and did not destroy or surrender it can be prosecuted. The key date is March 26, 2019.

Are there other devices that do the same thing as a bump stock?

Yes. The ATF has identified other devices and modifications that achieve similar effects, including binary triggers and certain types of cranks. These are also subject to the same legal restrictions. The law targets any device that allows a semi-automatic gun to fire at automatic rates, regardless of the specific mechanism.

Why did the ATF change its mind about bump stocks?

The ATF initially focused on the technical definition of how the gun fires — once per trigger pull — rather than the practical effect. After the Las Vegas shooting demonstrated the real-world danger, the agency reconsidered and concluded that the practical outcome (automatic-rate fire) was what the law intended to regulate, not the specific mechanism used to achieve it.