An “any other weapon,” or AOW, is a catch-all category under the National Firearms Act that covers concealable weapons which don’t fit the NFA’s other classifications like short-barreled rifles, machineguns, or suppressors. The definition at 26 U.S.C. § 5845(e) sweeps in disguised firearms, smooth-bore pistols designed to fire shotgun shells, and certain combination-barrel weapons.1Office of the Law Revision Counsel. 26 USC 5845 – Definitions Federal registration with ATF is required to possess one, though a 2025 law change reduced the making and transfer tax on an AOW to $0.
How Federal Law Defines an AOW
The statute reaches three distinct types of weapon:1Office of the Law Revision Counsel. 26 USC 5845 – Definitions
- Any weapon or device capable of being concealed on a person that fires a shot through the energy of an explosive. This is the broadest prong and captures most disguised firearms.
- A pistol or revolver with a smooth bore designed to fire a fixed shotgun shell.
- Weapons with paired shotgun and rifle barrels between 12 and 18 inches long, where only one shot can be fired from either barrel before manually reloading.
The definition also picks up any weapon in those categories that “may be readily restored to fire,” so a broken or disabled AOW doesn’t escape classification just because it can’t shoot at the moment.
What Doesn’t Qualify
The statute explicitly excludes two categories. A standard pistol or revolver with a rifled bore is not an AOW, even though it is concealable and fires by explosive energy.1Office of the Law Revision Counsel. 26 USC 5845 – Definitions That exclusion is what keeps every ordinary handgun in America out of the NFA. Weapons designed to be fired from the shoulder that cannot fire fixed ammunition are also excluded.
Overall length matters too. When a firearm with a vertical foregrip has an overall length greater than 26 inches, ATF generally does not treat it as an AOW because it no longer meets the “capable of being concealed on the person” element of the definition.
Common Examples
The most recognizable AOWs are disguised firearms. Pen guns look like writing instruments, cane guns resemble walking canes, and wallet guns fire while hidden inside a wallet holster. All of them satisfy the concealability-plus-explosive-energy prong because their entire design purpose is to not look like a firearm.
Smooth-bore pistols built to fire shotgun shells also fall squarely into AOW territory. A firearm manufactured from the start with a pistol grip, no shoulder stock, and a smooth bore isn’t technically a “shotgun” under the NFA, since the statutory definition of shotgun requires the weapon to be designed for shoulder firing. If that same firearm has an overall length under 26 inches, it lands in the AOW category rather than the short-barreled shotgun category.
Adding a vertical foregrip to a handgun can also create an AOW. ATF has long held that installing a vertical foregrip on a pistol means it’s no longer designed to be held and fired with one hand, and the person who installs it is “making” an NFA firearm that requires registration.2Bureau of Alcohol, Tobacco, Firearms and Explosives. Adding a Vertical Fore Grip to a Handgun Doing this without first filing the proper ATF paperwork is a federal crime.
Registering, Making, and Transferring an AOW
Anyone who wants to build or assemble an AOW must get ATF approval before starting. The process requires filing ATF Form 1, Application to Make and Register a Firearm, which serves as both the request for approval and the registration document.3Bureau of Alcohol, Tobacco, Firearms and Explosives. eForms Applications The applicant must provide identifying information, fingerprints, and a photograph.4Office of the Law Revision Counsel. 26 USC 5822 – Making Construction cannot begin until ATF has approved the Form 1. Building first and registering later is a federal crime.
Buying an existing, registered AOW uses ATF Form 4, Application for Tax Paid Transfer and Registration of a Firearm.3Bureau of Alcohol, Tobacco, Firearms and Explosives. eForms Applications The transferee submits identifying information, fingerprints, and photographs. ATF will deny the transfer if the person’s receipt or possession would violate federal, state, or local law.5Office of the Law Revision Counsel. 26 USC 5812 – Transfers You cannot take possession until ATF approves the transfer.
The federal tax on both making and transferring an AOW is currently $0. A 2025 amendment zeroed out the making tax and the transfer tax for all NFA firearms except machineguns and destructive devices.6Office of the Law Revision Counsel. 26 USC 5821 – Making Tax7Office of the Law Revision Counsel. 26 USC 5811 – Transfer Tax ATF approval and registration are still required; there is simply no payment.
Applicants and transferees must also send a copy of the completed application to the chief law enforcement officer in their locality as a notification, not for approval.8Bureau of Alcohol, Tobacco, Firearms and Explosives. Background Checks for Responsible Persons (Final Rule 41F)
Processing times have dropped in recent years. Current median waits are:9Bureau of Alcohol, Tobacco, Firearms and Explosives. Current Processing Times
- eForm 4, individual: 10 days
- eForm 4, trust: 26 days
- Paper Form 4, individual: 21 days
- Paper Form 4, trust: 24 days
These figures change regularly and represent medians, not guarantees.
Penalties for Unregistered Possession
The consequences for possessing an unregistered AOW are severe. Federal law prohibits receiving or possessing an unregistered firearm, possessing a firearm not registered to you, and transferring a firearm in violation of the NFA’s requirements.10Office of the Law Revision Counsel. 26 USC 5861 – Prohibited Acts A conviction carries a fine of up to $10,000, imprisonment of up to ten years, or both.11Office of the Law Revision Counsel. 26 USC 5871 – Penalties
This is where the AOW classification catches people off guard. Someone who attaches a vertical foregrip to a pistol without realizing they’ve just “made” an NFA firearm faces the same maximum penalty as someone caught with an unregistered machinegun. With the tax now at $0 and approval times relatively short, there is little reason to skip the process.
State Law Can Still Prohibit Possession
Federal registration alone may not be enough. Some states impose additional restrictions on NFA firearms, and a handful prohibit certain NFA categories outright. A firearm that is lawfully registered with ATF can still be illegal to possess under state or local law, and ATF will deny a Form 4 transfer if possession would violate the laws of the transferee’s state. Verify your state and local laws before acquiring any NFA firearm, because federal compliance does not override a state-level ban.