Firearms are classified under federal and state law by two main federal statutes plus whatever a state adds on top. The Gun Control Act of 1968 (GCA) sets the baseline categories for common weapons like handguns, rifles, and shotguns. The National Firearms Act of 1934 (NFA) pulls a narrower group of weapons into a stricter regime that requires federal registration. States then layer their own classifications, and a firearm that is unremarkable under federal law can be restricted or banned at the state line.
The Gun Control Act Categories
The GCA gives us the working definitions most gun owners deal with every day.1Office of the Law Revision Counsel. 18 USC 921 – Definitions
A handgun is a firearm with a short stock designed to be held and fired with one hand. Pistols and revolvers both fall here.
A rifle is a shoulder-fired weapon that sends a single projectile through a rifled barrel. A shotgun is a shoulder-fired weapon with a smooth bore that fires either multiple pellets or a single slug.
Neither definition sets a minimum barrel length on its own. Barrel length matters because dropping below it kicks the weapon into a stricter category. A rifle with a barrel under 16 inches becomes a short-barreled rifle. A shotgun with a barrel under 18 inches becomes a short-barreled shotgun. In either case, an overall length under 26 inches also triggers the reclassification, and both restricted forms are regulated by the NFA rather than the GCA.
The GCA definition of “firearm” is broader than most people expect. It includes not just complete weapons but also the frame or receiver of any weapon, plus silencers and destructive devices. A bare lower receiver in a box, without a barrel, stock, or trigger group, is legally a firearm for transfer and background-check purposes.
The National Firearms Act Categories
The NFA covers a specific set of weapons that Congress singled out for stricter treatment.2Bureau of Alcohol, Tobacco, Firearms and Explosives. National Firearms Act Every item in these categories must be registered in the National Firearms Registration and Transfer Record, and each transfer requires ATF approval.
Machine Guns
A machine gun is any weapon that fires more than one shot with a single pull of the trigger without reloading between shots. The definition reaches the frame or receiver of such a weapon and any part or combination of parts designed to convert a weapon into one.3Office of the Law Revision Counsel. 26 USC 5845 – Definitions
Federal law bans the transfer or possession of any machine gun not lawfully owned before May 19, 1986.4Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts The pool of transferable machine guns is frozen at whatever existed on that date. Ones still in private hands can be sold, but no new ones enter the civilian market. Government agencies and certain licensed dealers are exempt.
Short-Barreled Rifles and Shotguns
A short-barreled rifle (SBR) has a barrel under 16 inches or an overall length under 26 inches. A short-barreled shotgun (SBS) has a barrel under 18 inches or an overall length under 26 inches. Any weapon modified from a standard rifle or shotgun to fall below those measurements is also covered, regardless of how it left the factory.
Silencers
Silencers (also called suppressors) are devices attached to or built into a firearm to reduce the sound of a gunshot. The NFA treats them as their own category of regulated firearm, so a silencer requires the same registration paperwork as an SBR or machine gun.
Destructive Devices
This category is broader than the name suggests. It covers explosive items like bombs, grenades, mines, rockets with a propellant charge over four ounces, and missiles with an explosive charge over a quarter ounce. It also covers any weapon with a bore diameter larger than half an inch, with exceptions for shotguns and certain sporting rifles. The bore-diameter rule is why some large-caliber firearms end up on the NFA list while others receive a sporting exemption.
Any Other Weapon
The “Any Other Weapon” (AOW) category catches concealable weapons that don’t fit the other NFA slots: pen guns, cane guns, and revolvers with smooth bores designed to fire shotgun shells. Combination rifle-and-shotgun weapons with barrels between 12 and 18 inches also land here. Standard pistols and revolvers with rifled bores are specifically excluded, as are weapons designed to fire from the shoulder.
What NFA Classification Costs You
Owning any NFA firearm means filing paperwork with the ATF, submitting fingerprints and photographs, and passing a background check. Form 4 handles purchases from a manufacturer or dealer. Form 1 covers building an NFA firearm yourself.
The transfer tax used to be $200 for most NFA firearms and $5 for AOWs. The One Big Beautiful Bill Act, signed in 2025, changed that. As of January 1, 2026, the transfer tax is $0 for silencers, short-barreled rifles, short-barreled shotguns, and AOWs. Only machine guns and destructive devices still carry the $200 tax.5Office of the Law Revision Counsel. 26 USC 5811 – Transfer Tax The registration process itself is unchanged. You still need ATF approval, fingerprints, photographs, and a background check regardless of what the tax comes out to.
Antique Firearms and Curios and Relics
Two categories carve out lighter treatment for older and collectible firearms, and they are not the same thing.
Antique Firearms
An antique firearm is largely exempt from the GCA. The definition covers three groups: any firearm manufactured in or before 1898, replicas of pre-1899 firearms that don’t use modern rimfire or centerfire ammunition, and muzzle-loading weapons designed for black powder that can’t accept fixed ammunition. Because antiques fall outside the GCA’s definition of “firearm,” they can be bought, sold, and shipped without going through a licensed dealer and without a federal background check. State laws on antique firearms vary and can be more restrictive.
The NFA has its own antique exemption and also excludes collector’s items that the ATF determines are unlikely to be used as weapons, based on age, value, and design.
Curios and Relics
The ATF recognizes “curio or relic” (C&R) firearms as those with special collector interest beyond ordinary use. A firearm qualifies if it was manufactured at least 50 years ago, if a museum curator certifies its museum interest, or if it derives significant monetary value from being novel, rare, or historically associated.6Bureau of Alcohol, Tobacco, Firearms and Explosives. Curios and Relics Unlike antiques, C&R firearms remain regulated under the GCA. Collectors with a Type 03 Federal Firearms License can acquire C&R items across state lines directly from other licensees and individuals without routing the sale through a standard dealer.
Accessories and Parts That Have Shifted Categories
Some of the most consequential classification questions in recent years have not involved traditional weapon categories. They have involved accessories and unfinished parts that sit between existing definitions.
Bump Stocks
Bump stocks are aftermarket devices that use a rifle’s recoil to let the shooter fire at a rate approaching an automatic weapon while technically requiring a separate trigger pull for each shot. After the 2017 Las Vegas shooting, the ATF classified bump stocks as machine guns, effectively banning them. The Supreme Court struck the rule down in Garland v. Cargill (2024), holding that a semiautomatic rifle with a bump stock doesn’t meet the statutory definition of “machine gun” because it doesn’t fire more than one shot by a single function of the trigger and doesn’t do so automatically.7Supreme Court of the United States. Garland v. Cargill, 22-976 Bump stocks are no longer prohibited under federal law, but several states have enacted or maintained their own bans.8Bureau of Alcohol, Tobacco, Firearms and Explosives. Bump Stocks
Stabilizing Braces
Pistol stabilizing braces were originally designed to help disabled shooters fire large-format pistols one-handed. Because a brace attaches to the rear of a pistol and can functionally resemble a short rifle stock, the ATF in 2023 issued a rule reclassifying most braced pistols as short-barreled rifles. That would have forced millions of owners to register under the NFA. The rule was challenged, and in July 2025 the government dismissed its appeal in Mock v. Bondi, leaving in place a court order that vacated the rule entirely. Braced pistols are currently treated the same as any other handgun under federal law. Individual states may still impose their own restrictions.
Forced Reset Triggers
Forced reset triggers (FRTs) mechanically reset the trigger after each shot at high speed. The ATF has classified at least some FRT models as machine guns, and that classification has been the subject of ongoing litigation between manufacturers and the agency. This area of law remains unsettled. Check the current federal status before buying one.
Ghost Guns and Unfinished Frames
The GCA has always defined “firearm” to include the frame or receiver of a weapon, but the market for partially complete frames and kits pushed the question of what actually counts as a frame or receiver.1Office of the Law Revision Counsel. 18 USC 921 – Definitions In 2022, the ATF issued a final rule clarifying that “frame” and “receiver” include partially complete versions that can be readily finished, and that weapon parts kits qualify as firearms when they can be readily converted into functional weapons.9Bureau of Alcohol, Tobacco, Firearms and Explosives. Definition of Frame or Receiver and Identification of Firearms Companies selling unfinished frames and parts kits now face serialization and recordkeeping requirements similar to those for completed firearms, though the rule was challenged in federal court and reached the Supreme Court, and the enforcement picture has moved more than once. Check current ATF guidance before buying or building from an unserialized kit.
State Categories Federal Law Doesn’t Have
Federal law is the floor. States are free to build higher, and several state categories have no federal equivalent.
Assault Weapon Bans
Roughly a dozen states and the District of Columbia ban or heavily restrict firearms they classify as “assault weapons.” There is no federal assault weapon ban in effect. State definitions typically focus on features attached to a semiautomatic rifle: a detachable magazine combined with a pistol grip, a folding or telescoping stock, a flash suppressor, or a forward grip. The internal operation of the rifle usually doesn’t matter. Two rifles with identical firing mechanisms can land on opposite sides of the law depending on their external features. Some states extend similar feature-based definitions to semiautomatic pistols and shotguns.
Magazine Capacity Limits
More than a dozen states cap how many rounds a detachable magazine can hold. The most common threshold is 10 rounds, though a few states set the line at 12 or 15. These limits typically apply to both handgun and rifle magazines. Possessing, selling, or importing a magazine above the limit is usually the violation, though some states grandfather magazines owned before the effective date.
Preemption and Local Ordinances
Most states have preemption laws that stop cities and counties from writing firearm rules stricter than the state’s. In those states, one classification scheme applies everywhere. A handful of states allow local governments to pass their own firearm ordinances, which creates a patchwork where a weapon legal in one city may be restricted a few miles down the road. In a state without strong preemption, local ordinances matter as much as state law.
Why the Category Matters
Classification determines whether you need a background check to buy a weapon, whether you need to register it federally, how much tax you owe, whether you can move it across state lines, and what penalty you face for getting it wrong. Possessing an unregistered NFA firearm is a federal felony carrying up to 10 years in prison. Owning a post-1986 machine gun as a civilian is a separate federal crime.4Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts A well-intentioned modification, like shortening a rifle barrel below 16 inches without NFA registration, can turn a legal firearm into an illegal one on the workbench.
The classification landscape has moved faster in the past few years than in any comparable stretch. Cargill reversed the federal bump stock ban in 2024. The pistol brace rule came and went in under three years. Congress zeroed out the transfer tax for most NFA items effective 2026. Before you buy, build, or modify a firearm, verify the current federal and state classification rules at the time of the transaction rather than relying on guidance that may already be stale.