Background

To circumvent the significant restrictions on machine guns, the gun industry has marketed devices that can be attached to semiautomatic firearms and accelerate the weapon’s rate of fire so much that it approaches the rate of automatic machine gun fire. These devices, including bump-fire (or bump stock) and trigger crank devices, were designed to skirt the limits of federal law and increase casualties in a shooting.

What Are Bump Stocks?

Bump stocks are designed to circumvent laws restricting automatic weapons, allowing rifles to fire in quick succession, killing more people more efficiently.

Bump-fire devices replace a semiautomatic rifle’s standard shoulder stock and allow the weapon to smoothly slide (or “bump”) back and forth very rapidly between the shooter’s shoulder and trigger finger. By harnessing the weapon’s recoil or kickback, the bump stock causes the trigger to be engaged many times faster than a human could otherwise fire. When outfitted with a bump stock, some semiautomatic firearms can fire 400 to 800 rounds per minute.¹

In October 2017, a gunman in Las Vegas used multiple bump-fire devices to convert semiautomatic rifles into weapons that fired nine shots per second. He used those weapons to carry out the deadliest mass shooting attack in modern American history, killing 60 people and injuring hundreds at a country music festival. Although the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) implemented a rule after this shooting to regulate bump stocks as machine guns, the Supreme Court overturned that rule in its June 2024 Garland v. Cargill decision, meaning that these devices are now legal under federal law.

Trigger cranks attach to a firearm’s trigger guard and similarly enable a shooter to repeatedly pull the trigger in very rapid succession by simply rotating the crank. Trigger cranks are not classified as “machine guns” by the ATF, and are thus still legal to own in most states.

Summary of Federal Law

Federal law does not address bump stocks and similar acceleration devices, although it does ban “any part designed and intended solely and exclusively… for use in converting a weapon into a machinegun.”² 

In response to the 2017 Las Vegas shooting, the ATF amended its regulations to find bump stocks subject to this ban.³ However, in June 2024 the Supreme Court issued its opinion in Garland v. Cargill, overruling this regulation and finding that a bump stock is not a “part designed and intended solely and exclusively… for use in converting a weapon into a machinegun,” so bump stocks are now legal under federal law.

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Summary of State Law

Sixteen states and the District of Columbia have taken steps to increase security regarding the use of bump stocks and trigger activators.

Because each state defines these devices differently, these laws vary in strength.

California bans the possession, manufacture, import, sale, gift, or lease of “multiburst trigger activator[s],”⁴ defined as either:

• A device designed or redesigned to be attached to, built into, or used in conjunction with a semiautomatic firearm, which allows the firearm to discharge two or more shots in a burst by activating the device.

• A manual or power-driven trigger activating device constructed and designed so that when attached to, built into, or used in conjunction with a semiautomatic firearm it increases the rate of fire of that firearm.⁵

The penalty for possession is imprisonment for up to one year.⁶

Connecticut bans the possession, manufacture, sale, or transfer of “rate of fire enhancement[s],” defined as:

“[A]ny device, component, part, combination of parts, attachment or accessory that:

• Uses energy from the recoil of a firearm to generate a reciprocating action that causes repeated function of the trigger, including, but not limited to, a bump stock;
• Repeatedly pulls the trigger of a firearm through the use of a crank, lever or other part, including, but not limited to, a trigger crank; or
• Causes a semiautomatic firearm to fire more than one round per operation of the trigger, where the trigger pull and reset constitute a single operation of the trigger, including, but not limited to, a binary trigger system.”⁷

Violation of this section is a class D misdemeanor for people who have firearms permits or eligibility certificates, and a class D felony for those who do not.⁸ 

Delaware bans the manufacture, possession, sale, and transfer of bump stocks, trigger cranks, and rapid fire devices.

• “Bump stock” means an after-market device that increases the rate of fire achievable with a semiautomatic rifle by using energy from the recoil of the weapon to generate a reciprocating action that facilitates repeated activation of the trigger.
• “Trigger crank” means an after-market device designed and intended to be added to a semiautomatic rifle as a crank operated trigger actuator capable of triggering multiple shots with a single rotation of the crank.
• “Rapid fire device” means a part, kit, tool, accessory, or device that increases the rate of fire of a semiautomatic firearm to a rate of fire that mimics the rate of fire of a machine gun.⁹

Florida bans the possession, sale, and transfer of “bump-fire stock[s],” defined as:

“[A] conversion kit, a tool, an accessory, or a device used to alter the rate of fire of a firearm to mimic automatic weapon fire or which is used to increase the rate of fire to a faster rate than is possible for a person to fire such semiautomatic firearm unassisted by a kit, a tool, an accessory, or a device.”¹⁰

Violation of this section is a felony of the third degree. Though Florida bans only bump stocks by name, the definition of bump-fire stocks is broad enough to include other devices that enhance the rate of semiautomatic firearms.

In 2018, Hawaii prohibited the manufacture, sale, or possession of bump stocks which are defined as “a butt stock designed to be attached to a semiautomatic firearm and designed… to increase the rate of fire… by using energy from the recoil of the firearm to generate a reciprocating action that facilitates repeated activation of the trigger.”¹¹ 

Hawaii also prohibits two additional types of trigger activators:

(A) “Trigger cranks,” defined as “any device to be attached to a semiautomatic firearm that repeatedly activates the trigger of the firearm through the use of a lever or other part that is turned in a circular motion…” and

(B) “Multiburst trigger activators,” which are:

(1) Devices that simulate automatic gunfire by allowing standard function of a semiautomatic firearm with a static positioned trigger finger or a device that fires multiple shots with the pull and release of the trigger; or

(2) Manual or power-driven trigger activating devices constructed and designed so that when attached to a semiautomatic firearm they simulate automatic gunfire.¹²

Iowa bans the sale of “a manual or power-driven trigger activating device constructed and designed so that when attached to a firearm [it] increases the rate of fire of the firearm.”¹³

Illinois passed legislation in early 2023—as part of a broad, comprehensive bill regulating the availability of assault weapons, .50 caliber rifles, and large-capacity magazines—to restrict the manufacture, sale, offer to sale, possession, purchase, importation, transfer, or use of any device, part, kit, tool, accessory, or combination of parts that is designed to and functions to increase the rate of fire of a semiautomatic firearm above the standard rate of fire for semiautomatic firearms not equipped with such a device or part(s).¹⁴

Maryland bans the possession, sale, transfer, or transportation of rapid fire trigger activators.

“Rapid fire trigger activator” means any device, including a removable manual or power-driven activating device, constructed so that, when installed in or attached to a firearm:

• the rate at which the trigger is activated increases; or

• the rate of fire increases.¹⁵

Violation of this section is a misdemeanor. Maryland offers an exception to this restriction for those who have applied for authorization from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) before October 1, 2018. Effective October 1, 2019, this exception will apply only to those who have received authorization from the ATF by that date.¹⁶

Massachusetts bans possession of bump stocks and trigger cranks as part of its machine gun ban.

• “Machine gun,” a weapon of any description, … ; provided, however, that “machine gun” shall include bump stocks and trigger cranks.¹⁷ A bump stock is defined as any device for a weapon that increases the rate of fire achievable with such weapon by using energy from the recoil of the weapon to generate a reciprocating action that facilitates repeated activation of the trigger..¹⁸

• Whoever, except as provided by law¹⁹, possesses a machine gun, … , shall be punished by imprisonment in the state prison for life, or for any term of years …²⁰

Minnesota bans²¹ the ownership, possession, or operation of a trigger activator, which is defined as:

• A removable manual or power driven trigger activating device constructed and designed so that, when attached to a firearm, the rate at which the trigger may be pulled increases and the rate of fire of the firearm increases to that of a machine gun; or

• A device that allows a semiautomatic firearm to shoot more than one shot with a single pull of the trigger or by harnessing the recoil of energy of the semiautomatic firearm to which it is affixed so that the trigger resets and continues firing without additional physical manipulation of the trigger.²²

Nevada prohibits devices, parts or combinations of parts, and modifications to firearms that eliminate the need for the operator of a semiautomatic firearm to make a separate movement for each individual function of the trigger and:

• Materially increases the rate of fire of the semiautomatic firearm; or

• Approximates the action or rate of fire of a machine gun.²³

New Jersey bans the possession of bump stocks and trigger cranks.²⁴

• “Bump stock” means any device or instrument for a firearm that increases the rate of fire achievable with the firearm by using energy from the recoil of the firearm to generate a reciprocating action that facilitates repeated activation of the trigger.

• “Trigger crank” means any device or instrument to be attached to a firearm that repeatedly activates the trigger of the firearm through the use of a lever or other part that is turned in a circular motion; provided, however, the term shall not include any weapon initially designed and manufactured to fire through the use of a crank or lever.²⁵

Possession is a crime of the third degree. This ban, due to the narrow definitions of bump stock and trigger crank, does not ban all devices that can increase firing rate.²⁶

Rhode Island bans bump stocks and trigger cranks as well as other devices that increase the rate of fire of semiautomatic firearms:

• “It shall be unlawful for any person to possess a bump-fire device, binary trigger, trigger crank, or any other device that when attached to a semi-automatic weapon allows full-automatic fire.²⁷ A bump-fire stock is defined as any device that replaces a semi-automatic weapon’s standard stock and is designed to slide back and forth rapidly, harnessing the weapon’s recoil to rapidly fire the weapon.²⁸ Those who violate this section are subject to one to ten years of imprisonment of a fine of up to $10,000.”²⁹

In Vermont, a “bump-fire stock” means a butt stock designed to be attached to a semiautomatic firearm and intended to increase the rate of fire achievable with the firearm to that of a fully automatic firearm by using the energy from the recoil of the firearm to generate a reciprocating action that facilitates the repeated activation of the trigger. Possession of a bump-fire stock is prohibited.³⁰ 

Virginia bans the manufacture, importation, sale, possession, transfer, and transportation of trigger activators, which include any device designed to allow a semiautomatic firearm to shoot more than one shot by a single pull of the trigger by harnessing the recoil energy of the firearm so that the trigger resets and continues firing without additional physical manipulation of the trigger by the shooter.³¹ Violation of this law is punishable as a felony.³²

In 2018 Washington prohibited any person from manufacturing, owning, buying, selling, loaning, furnishing, transporting, or having in his or her possession or under his or her control “bump-fire stocks.”³³ Washington defines a “bump-fire stock” as “a butt stock designed to be attached to a semiautomatic firearm with the effect of increasing the rate of fire achievable with the semiautomatic firearm to that of a fully automatic firearm by using energy from the recoil of the firearm to generate a reciprocating action that facilitates repeated activation of the trigger.”³⁴

Key Legislative Elements

The features listed below are intended to provide a framework from which policy options may be considered. A jurisdiction considering new legislation should consult with counsel.

• A prohibition on the manufacture, import, sale, offer for sale, transfer, and possession of a trigger activator (or equivalent term), including bump stocks and similar devices.
• The definition of trigger activator (or equivalent term) should be broad enough to encompass all devices, including both firearm accessories and firearm parts, that are designed and function to materially increase the rate of fire beyond the standard rate of fire for a semiautomatic firearm.

1. The “Bump Stocks” Used in the Las Vegas Shooting May Soon Be Banned, Economist (Oct. 6, 2017).[↩]
2. 18 U.S.C. § 921(a)(24), 922(o); 26 U.S.C. § 5845(a), (b).[↩]
3. 83 Fed. Reg. 66514. The agency rule stated: “For purposes of this definition, the term ‘automatically’ as it modifies ‘shoots, is designed to shoot, or can be readily restored to shoot,’ means functioning as the result of a self-acting or self-regulating mechanism that allows the firing of multiple rounds through a single function of the trigger; and ‘single function of the trigger’ means a single pull of the trigger and analogous motions. The term ‘machinegun’ includes a bump-stock-type device, i.e., a device that allows a semi-automatic firearm to shoot more than one shot with a single pull of the trigger by harnessing the recoil energy of the semi-automatic firearm to which it is affixed so that the trigger resets and continues firing without additional physical manipulation of the trigger by the shooter.”[↩]
4. Cal. Penal Code, § 32900.[↩]
5. Cal. Penal Code, § 16930. The previous version of this section has slightly different wording: “A device designed or redesigned to be attached to a semi-automatic firearm, which allows the firearm to discharge two or more shots in a burst by activating the device.”[↩]
6. Cal. Penal Code, § 32900.[↩]
7. Conn. Gen. Stat. § 53-206g. An exception is provided for firearms manufacturers fulfilling a military contract.[↩]
8. Id.[↩]
9. Del. Code Ann. tit. 11, § 1444(a)(6).[↩]
10. Fla. Stat. § 790.222.[↩]
11. Haw. Rev. Stat. § 134-8.5.[↩]
12. Id.[↩]
13. Iowa Code § 724.29.[↩]
14. 720 ILCS 5/24-1(a)(14).[↩]
15. Md. Code Ann., Crim. Law § 4-301(m).[↩]
16. Md. Code Ann., Crim. Law § 4-305.1.[↩]
17. Mass. Ann. Laws ch. 140, § 121.[↩]
18. Id.See also definition of “trigger crank.”[↩]
19. The only civilians permitted to possess machine guns are firearms instructors (only for firearm instruction to police) and licensed collectors. Mass. Ann. Laws ch. 140, § 131.[↩]
20. Mass. Ann. Laws ch. 269, § 10(c).[↩]
21. Minn. Stat. § 609.67, Subd. 1.[↩]
22. Minn. Stat. §609.67, Subd. 2.[↩]
23. Nev. Rev. Stat. § 202.274.[↩]
24. N.J. Stat. § 2C:39-3(l).[↩]
25. N.J. Stat. § 2C:39-1(ee), (ff).[↩]
26. N.J. Stat. § 2C:39-3(l).[↩]
27. 11 R.I. Gen. Laws § 47-8(d).[↩]
28. 11 R.I. Gen. Laws. § 47-2(4). See 11 R.I. Gen. Laws § 47-2(3) and § 47-2(19) for definitions of “binary trigger” and “trigger crank”.[↩]
29. 11 R.I. Gen. Laws § 47-8(d).[↩]
30. 13 Vt. Stat. Ann. § 4022.[↩]
31. Va. Code Ann. § 18.2-308.5:1.[↩]
32. Id.[↩]
33. Wash. Rev. Code Ann. § 9.41.190(1).[↩]
34. Wash. Rev. Code Ann. § 9.41.010(5).[↩]