The Bumping Unlawful Machinegun Parts Act (BUMP Act) would amend title 18 to prohibit devices that convert semiautomatic firearms into machineguns or that materially increase their rate of fire. It also defines what counts as a semiautomatic firearm and lays out a 120‑day registration window for firearms that were modified before enactment.
The bill updates the National Firearms Act framework by aligning it with these new definitions.
The legislation is designed to close loopholes that could allow rapid-fire devices to be marketed or transferred by saying a gun is still “semiautomatic.” It creates a regulated path for owners with pre-modified firearms to come into compliance and clarifies which government entities and activities are exempt. Compliance would fall under existing ATF and IRS administration, with penalties for violations.
This is a substantive change to how certain firearm parts and modifications are treated under federal law and would affect manufacturers, retailers, owners, and regulators alike.
At a Glance
What It Does
It adds a new definition of semiautomatic firearm and creates a prohibition on devices that increase firing rate or mimic machinegun action, along with a 120‑day registration requirement for pre‑modification firearms and related amendments to tax code references.
Who It Affects
Manufacturers, importers, retailers of firearm parts, and gun owners who have modified semiautomatic firearms; plus federal, state, and local regulators enforcing firearms laws.
Why It Matters
It closes identified loopholes by standardizing the definition of key terms and creating a registration mechanism, thereby strengthening enforcement against unlawful modifications and ensuring traceable ownership.
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What This Bill Actually Does
The bill starts by rewriting how a semiautomatic firearm is defined. It says a semiautomatic firearm must pull the next cartridge into the chamber after each trigger pull and still require a separate trigger action.
It also confirms that such a firearm is not a machinegun under current law. With that definition in place, the bill adds a new prohibition: it makes it unlawful to import, manufacture, sell, transfer, or possess devices that (a) significantly speed up firing, (b) eliminate the separate trigger action for each shot, or (c) otherwise approximate machinegun behavior when attached to a semiautomatic firearm.
This would cover conversion devices and any parts designed to increase the rate of fire.
The law introduces a 120‑day window for owners who already have a semiautomatic firearm that has been modified as described to register it with the IRS under the existing recordkeeping framework. The bill also carves out exemptions for government actors and certain transfers that occur before the date of enactment.
In addition, it amends the National Firearms Act to explicitly include semiautomatic firearms modified as described in the new section, tying modified firearms to the federal regulatory regime. The overall effect is a tighter containment of rapid‑fire capabilities and clearer enforcement paths for regulators and police.For compliance professionals, dealers, and owners, this means a shift in how devices and modifications are categorized and regulated.
It requires clear documentation of any pre‑existing modifications, adherence to registration timelines, and careful consideration of what constitutes a prohibited device. Regulated parties should anticipate ATF and IRS oversight expanding to cover these newer categories, with penalties for non‑compliance and mechanisms to facilitate enforcement.
The Five Things You Need to Know
The bill adds a new 18 U.S.C. 922(v) prohibiting import, sale, manufacture, transfer, or possession of devices that increase the rate of fire or mimic machinegun action.
A new definition of “semiautomatic firearm” is inserted into 18 U.S.C. 921(a), detailing the firing, cycling, and trigger requirements.
Owners of semiautomatic firearms modified before enactment must register the firearm within 120 days.
There are exemptions for government importation and for lawful possession or transfers prior to enactment.
The National Firearms Act is amended to recognize semiautomatic firearms modified as described in 922(v)(1)(C).
Section-by-Section Breakdown
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Definition: semiautomatic firearm
The bill inserts a new definition of a semiautomatic firearm into 18 U.S.C. 921(a). It specifies that a semiautomatic firearm uses energy from the firing cartridge to cycle the action, requires a separate trigger pull for each shot, and is not a machinegun. This creates a precise legal baseline for what counts as semiautomatic and clarifies when a firearm would be treated as a non-machinegun under the revised regime. This definitional clarity matters for enforcement and for determining which devices and modifications fall under the new prohibitions.
Prohibition on conversion and rate‑of‑fire devices
The bill adds a new subsection (v) to 18 U.S.C. 922. It bans (A) devices that materially increase the rate of fire or imitate machinegun operation when attached to a semiautomatic firearm, (B) devices or parts designed to increase rate of fire by removing normal trigger‑level separations, and (C) semiautomatic firearms that have been modified to materially increase rate of fire or mimic machinegun action. This creates a broad prohibition on both devices and modifications that enable rapid firing beyond the designed capacity of a standard semiautomatic firearm.
Registration of pre‑modified semiautomatic firearms
Paragraph (2) requires that, within 120 days after enactment, any person who lawfully owns a semiautomatic firearm modified as described in subsection (1)(C) must register the firearm as prescribed in the Internal Revenue Code (26 U.S.C. 5841). This creates a paper trail for modified firearms and aligns ownership with an identifiable custody history, aiding traceability and enforcement.
Exemptions from the prohibition
Paragraph (3) provides exemptions for imports, manufacturing, transfer to, or possession by the United States or its agencies, or by States, Tribes, or political subdivisions, under the authority of those entities. Paragraph (4) clarifies that lawful transfers or possesssions of pre‑modification semiautomatic firearms, made before enactment and registered under paragraph (2), are exempt from the prohibition.
Cross‑reference: add subsection (v)
The bill amends 18 U.S.C. 924(a)(2) to replace references to the prior subsections with an updated cross‑reference that includes subsection (v). This ensures that penalties and enforcement authorities apply to the new prohibitions and devices described in 922(v), tying the new regime into existing criminal enforcement provisions.
NFA amendment to include modified semiautomatic firearms
The Internal Revenue Code’s NFA list is amended by striking a previous descriptor and inserting a reference to semiautomatic firearms defined in 18 U.S.C. 921 that are modified as described in 922(v)(1)(C). The change places these firearms within the regulatory framework of the NFA, reinforcing control over possession, transfer, and registration through the tax code mechanism.
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Every bill creates winners and losers. Here's who stands to gain and who bears the cost.
Who Benefits
- ATF and other regulators gain a clearer definitional framework and a centralized enforcement pathway for devices and modifications that increase firing rate.
- Law enforcement agencies and prosecutors benefit from better tools to identify, prosecute, and deter unlawful modifications and attachment devices.
- Public safety organizations gain a policy mechanism to reduce rapid‑fire equipment in circulation and support safer firearms standards.
- State and local governments gain harmonized rules that aid enforcement and reduce loopholes in interstate commerce.
- Compliant firearm manufacturers and retailers benefit from a standardized market environment with clearer compliance expectations.
Who Bears the Cost
- Firearm owners who have or acquire modified semiautomatic firearms may incur registration costs and potential penalties for noncompliance if they miss the registration deadline.
- Importers, manufacturers, and retailers of conversion devices face compliance costs, licensing requirements, and potential inventory write‑offs if products are deemed prohibited.
- Regulatory agencies (ATF, IRS, and state authorities) must allocate resources to administer the new registrations, enforcement actions, and reporting requirements.
- Small businesses in the firearm parts ecosystem may experience reduced product diversity or market changes due to the prohibitions and new definitions.
- States and Tribes may incur administrative costs associated with enforcing the new rules at the local level.
Key Issues
The Core Tension
The central dilemma is balancing public safety with practical enforceability: the bill aims to stop rapid‑fire devices by broad prohibitions and a registration regime, but defining “rate of fire” and “modification” in a way that is both precise and workable across firearm platforms is inherently challenging and could produce enforcement disputes.
The bill’s approach hinges on precise definitional clarity and a broad prohibition that could sweep in a wide range of devices and modifications. One key design question is how “materially increases the rate of fire” will be interpreted in practice, given differences in firearm platforms and ammunition.
The registration requirement for pre‑modified firearms also raises questions about how retroactive compliance will be verified and how exemptions will be validated in cross‑jurisdictional contexts. Enforcement‑level considerations include the risk of overreach in classification and the potential for disputes over what constitutes an “attachment” or a device that “approximates” machinegun action.
A second tension is the interaction with the tax framework (NFA) and how the registration regime will interface with ongoing possession and transfer rules. While the bill seeks to close loopholes, it may create new gray areas for owners who have legally modified firearms prior to enactment but face ambiguous categorization under the new definitions.
Policy makers will need to resolve questions about grandfathering, recordkeeping, and resource allocation for enforcement to ensure the measure is practical and enforceable without unduly burdening lawful ownership.
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