Possessing a machine gun conversion device is a federal felony punishable by up to 10 years in prison and a fine as high as $250,000. The penalties for a machine gun conversion device don’t depend on whether the part is ever installed, whether you own a firearm at all, or how the device came into your hands. Federal law treats the part itself as a machine gun, and the 1986 ban on civilian machine gun possession applies to it with full force. When a device turns up alongside a violent crime or drug trafficking offense, the exposure jumps to a mandatory 30 years on top of the underlying sentence.
What Federal Law Treats as a Conversion Device
The National Firearms Act defines a machine gun as any weapon that fires more than one shot per trigger pull without manual reloading. The same definition, at 26 U.S.C. § 5845(b), reaches any individual part, or combination of parts, designed and intended to convert a weapon into a machine gun.1Office of the Law Revision Counsel. 26 USC 5845 – Definitions The part is the machine gun under federal law, whether or not it has ever touched a firearm.
The definition stretches further. If you possess a set of parts that could be assembled into a functioning machine gun, that collection qualifies as a machine gun too. Nothing has to be put together. Having the components under your control is enough.2Bureau of Alcohol, Tobacco, Firearms and Explosives. NFA Handbook – Appendix B This idea, sometimes called constructive possession, means that keeping a drop-in auto sear alongside the right rifle components can be charged as possession of an unregistered machine gun even though nothing has been modified or combined.
The devices most often prosecuted fall into a few categories:
- Glock switches, small attachments that replace a pistol’s slide cover plate and cause the weapon to cycle continuously as long as the trigger is held down.
- Drop-in auto sears, metal components that bypass the internal disconnect inside certain rifle receivers to enable fully automatic fire.
- Lightning links, which connect a rifle’s bolt carrier to the sear so the hammer releases automatically each time the bolt closes.
Manufacturing method is irrelevant. A plastic auto sear produced on a consumer 3D printer is treated the same as a machined steel one, and federal prosecutors have brought cases against people running small printing operations out of their homes.3Department of Justice. Machinegun Conversion Devices Fact Sheet An Indianapolis man who manufactured and sold 3D-printed Glock switches and auto sears was sentenced to seven and a half years in federal prison.4Bureau of Alcohol, Tobacco, Firearms and Explosives. Trafficker of 3D-Printed Glock Switches and Auto-Sears Sentenced to Over Seven Years in Federal Prison
Why Possession Alone Is a Crime
The NFA has regulated machine guns since 1934, but the date that matters for conversion devices is May 19, 1986. That is when the Firearm Owners’ Protection Act took effect, adding 18 U.S.C. § 922(o), which flatly prohibits any person from possessing or transferring a machine gun.5Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts The only civilian exception is for machine guns lawfully possessed and registered before that date.
Almost every conversion device on the market today was made well after 1986, so no legal path exists for a civilian to acquire one. Buying a part online, receiving one as a gift, picking one up at a gun show, or printing one at home is the same federal offense. The device itself is the contraband.
Prison Time and Fines for Simple Possession
A conviction for possessing or transferring a machine gun conversion device carries up to 10 years in federal prison under 18 U.S.C. § 924(a), the penalty provision for the § 922(o) possession ban.6Office of the Law Revision Counsel. 18 USC 924 – Penalties Prosecutors can also charge under the NFA itself. Section 5871 of Title 26 sets the same 10-year maximum along with a fine of up to $10,000 for possessing an unregistered NFA firearm.7Office of the Law Revision Counsel. 26 USC 5871 – Penalties When the charge falls under the Gun Control Act rather than the NFA, the maximum fine rises to $250,000 under the general federal sentencing statute.8Office of the Law Revision Counsel. 18 USC 3571 – Sentence of Fine
Each device counts as a separate violation. A person caught with three Glock switches faces three counts, and a judge can order the sentences to run consecutively. Cases involving multiple devices or any sign of distribution routinely produce sentences well above the floor.
The 30-Year Minimum When Another Crime Is Involved
Penalties climb sharply when a conversion device is tied to another offense. Under 18 U.S.C. § 924(c), anyone who uses or carries a machine gun during a federal crime of violence or a drug trafficking offense faces a mandatory minimum of 30 years in prison.6Office of the Law Revision Counsel. 18 USC 924 – Penalties That term stacks on top of whatever the underlying offense carries and cannot be served concurrently. A person convicted of drug trafficking who had a pistol with a Glock switch faces the drug sentence and a separate, consecutive 30-year minimum for the machine gun.
Consequences That Outlast the Sentence
A conversion device conviction is a felony, which triggers a permanent federal ban on possessing any firearm or ammunition. Anyone convicted of a crime punishable by more than one year in prison falls under that prohibition for life.5Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts The prohibition reaches every type of firearm, not just machine guns, and violating it is a separate felony carrying its own 10-year sentence.
Forfeiture is the other tail. Under 18 U.S.C. § 924(d), firearms connected to a knowing violation of the machine gun ban are subject to forfeiture. That means losing not only the conversion device but potentially any firearm associated with the offense.6Office of the Law Revision Counsel. 18 USC 924 – Penalties
Two Devices That Do Not Carry These Penalties
Two products have generated real confusion and are worth naming, because they are not machine gun conversion devices under current federal law even though the ATF once tried to classify them that way.
In June 2024, the Supreme Court held in Garland v. Cargill that a bump stock does not turn a semi-automatic rifle into a machine gun. The Court reasoned that a bump stock still requires the trigger to reset between each shot and demands continuous manual effort from the shooter, so each shot results from a separate function of the trigger and falls outside the statutory definition.9Supreme Court of the United States. Garland v Cargill
Forced reset triggers went the same way. In July 2024, a federal district court in Texas ruled that Rare Breed FRT-15s and Wide Open Triggers are not machine guns under the NFA, and a later settlement bars the federal government from enforcing the machine gun ban against people who possess these specific devices.10Bureau of Alcohol, Tobacco, Firearms and Explosives. Rare Breed Triggers FRT-15s and Wide-Open Triggers WOTs Return These devices speed up the mechanical cycle of the trigger but still fire only one round per trigger function. Switches, sears, and links, which let a weapon keep firing from a single trigger pull, remain squarely inside the machine gun definition and carry every penalty above.