Under federal law, a rifle barrel has to be at least 16 inches long, and the whole firearm has to measure at least 26 inches from end to end. Miss either number and the gun is no longer a standard rifle. It becomes a short-barreled rifle under the National Firearms Act, which means federal registration, a $200 tax, and felony exposure if you skip the paperwork.
The Two Numbers That Matter
The NFA defines a regulated “firearm” to include any rifle with a barrel shorter than 16 inches, and any rifle with an overall length under 26 inches counts the same way.1Office of the Law Revision Counsel. 26 USC 5845 Definitions Both thresholds have to be cleared. A 16-inch barrel on a rifle that folds down to 25 inches overall is still an SBR.2Bureau of Alcohol, Tobacco, Firearms and Explosives. Chapter 2 – What Are Firearms Under the NFA
Meet both minimums and you have an ordinary Title I firearm, purchased with a standard background check and no special registration. Fall below either one and you’re in NFA territory. Shotguns follow a parallel rule with an 18-inch barrel minimum and the same 26-inch overall length.
How the ATF Measures Barrel Length
Barrel length is measured from the closed bolt or breech face to the farthest end of the barrel, including any permanently attached muzzle device. The accepted method is to drop a cleaning rod or dowel into the barrel until it stops against the bolt face, mark the rod at the muzzle, and measure the marked length.2Bureau of Alcohol, Tobacco, Firearms and Explosives. Chapter 2 – What Are Firearms Under the NFA The action has to be closed and the firearm assembled. A barrel measured loose on a workbench won’t give you the legally relevant number.
When a Muzzle Device Counts
Flash hiders, muzzle brakes, and compensators can add to your legal barrel length, but only if they’re permanently attached. The ATF recognizes three methods: full-fusion gas or electric steel-seam welding, high-temperature silver soldering at a 1,100°F flow point, and blind pinning with the pin head welded over.2Bureau of Alcohol, Tobacco, Firearms and Explosives. Chapter 2 – What Are Firearms Under the NFA
A muzzle device you can thread on and off by hand adds nothing to your legal length. This trips up buyers of 14.5-inch barrels who assume the factory flash hider gets them to 16. It can, but only after a gunsmith pins and welds it in a way that makes removal destructive.
What Counts as a Rifle in the First Place
The 16-inch rule only applies to rifles. Under the NFA, a rifle is a weapon designed to be fired from the shoulder that sends a single projectile through a rifled bore.1Office of the Law Revision Counsel. 26 USC 5845 Definitions A firearm built as a pistol, without a stock and never intended to be shouldered, is not a rifle, so the 16-inch minimum doesn’t reach it. That’s why AR-platform pistols with short barrels can exist legally without NFA registration. Take a rifle receiver and cut the barrel below 16 inches, though, and you’ve made an SBR.
On stabilizing braces, the ATF’s 2023 rule that would have reclassified many braced pistols as short-barreled rifles was found unlawful by federal courts in the Fifth and Eighth Circuits, and the Department of Justice dropped its appeal in early 2025. As of 2026, the rule is vacated and unenforceable, and braced pistols are not classified as SBRs.
If Your Barrel Is Under 16 Inches
A rifle with a barrel shorter than 16 inches, or an overall length under 26 inches, is a short-barreled rifle. Owning one lawfully requires registering it with the ATF and paying a $200 tax. The tax has been $200 since the NFA passed in 1934. It was set high to discourage ownership during the Depression and has never been adjusted.3Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). National Firearms Act (NFA)
You register before you build. If you already own a rifle and want to shorten the barrel, or you’re assembling one from parts, ATF Form 1 has to be approved first. If you’re buying a factory-built SBR from a licensed dealer, the dealer runs the transfer on ATF Form 4. Both routes require fingerprints, a photo, local law enforcement notification, and the $200 tax. Cutting the barrel or taking possession before approval creates the same violation as never filing at all.
Penalties for Going Under Without Paperwork
Federal law makes it a crime to possess any NFA firearm not registered to you in the National Firearms Registration and Transfer Record.4Office of the Law Revision Counsel. 26 US Code 5861 – Prohibited Acts There is no grace period and no way to register after the fact. The NFA contains no mechanism for a person to register an unregistered NFA firearm already in their possession.3Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). National Firearms Act (NFA)
A conviction carries up to 10 years in federal prison and a fine of up to $250,000 for an individual.5ATF. NFA Handbook – Chapter 15 – Penalties and Sanctions Because it’s a felony, a conviction also ends your right to own any firearm going forward. The law doesn’t distinguish between intent and mistake. Cutting a barrel a quarter-inch too short in a home gunsmithing project creates the same legal exposure as building an SBR on purpose.
Constructive Possession
The ATF has historically treated ownership of all the parts needed to assemble an unregistered NFA firearm as possession of that firearm, even when the parts aren’t put together. If you own a rifle and a spare barrel shorter than 16 inches, and there’s no other lawful firearm the short barrel fits, that combination can draw charges. If you don’t have a registered SBR or a pistol platform the short barrel belongs to, don’t keep the short barrel.
State Law Can Be Stricter
Federal approval doesn’t override state law. Several states and the District of Columbia ban civilian SBR ownership outright, and no federal tax stamp makes one legal in those jurisdictions. Others require state-level permits on top of federal registration. Check your state firearms law before you start any NFA paperwork. The ATF will deny a Form 1 or Form 4 for a firearm that isn’t legal to possess where you live.
Hunting rules are separate again. Some states set their own minimum barrel lengths for hunting specific game, and those rules change season to season. If you plan to hunt with a rifle at or near the 16-inch federal floor, look up the current regulations from your state wildlife agency before the trip.