Colorado short barrel rifle laws make possession a class 5 felony by default, but you can legally own one if you register it through the federal National Firearms Act first and keep proof of that registration available.1Justia Law. Colorado Code 18-12-102 – Possessing a Dangerous or Illegal Weapon The state and federal governments impose separate penalties for the same violation, and the firearm itself is subject to permanent forfeiture, so the details are worth getting right.
What Counts as a Short-Barreled Rifle
Under federal law, a rifle is short-barreled if the barrel is under 16 inches, or if the overall weapon, made from a rifle, is under 26 inches.2Legal Information Institute. 18 USC 921(a)(8) – Definition of Short-Barreled Rifle The overall-length rule catches rifles cut down below 26 inches even when the barrel itself is still 16 inches or longer.
Colorado uses the term “short rifle” and groups it with machine guns, silencers, short shotguns, and machine gun conversion devices under the label “dangerous weapon.”1Justia Law. Colorado Code 18-12-102 – Possessing a Dangerous or Illegal Weapon The moment a rifle drops below either federal threshold, it is a dangerous weapon under state law and an NFA firearm under federal law. Both regimes apply.
Why NFA Registration Is Your Defense in Colorado
Colorado does not ban short rifles outright. It treats possession as a class 5 felony and then provides an affirmative defense for anyone who holds “a valid permit and license for possession of such weapon.”1Justia Law. Colorado Code 18-12-102 – Possessing a Dangerous or Illegal Weapon Your approved ATF tax stamp is that permit and license.
The word “affirmative” carries weight. Ordinarily the state proves every element of a crime. With an affirmative defense, the burden is on you to prove your registration was valid and current when you were found in possession. Federal law separately requires you to retain proof of registration and produce it on request.3Office of the Law Revision Counsel. 26 USC 5841 – Registration of Firearms Keep a copy of the approved form somewhere you can actually reach it, not buried at home while the rifle is in your truck.
Registering Federally: Form 1 or Form 4
Which ATF form applies depends on how you are acquiring the rifle. Form 1 covers making an NFA firearm yourself, such as installing a short barrel on a rifle you already own. Form 4 covers buying or receiving a short rifle from a dealer or another individual.4Bureau of Alcohol, Tobacco, Firearms and Explosives. eForms Applications
Both forms require the same core documentation from each applicant: a 2×2-inch frontal passport-style photo taken within the past year, two FBI Form FD-258 fingerprint cards, a National Instant Criminal Background Check System check (your Social Security number is optional but speeds it up), and notification to your local chief law enforcement officer through the responsible person questionnaire.5Bureau of Alcohol, Tobacco, Firearms and Explosives. National Firearms Act Responsible Person Questionnaire
The NFA imposes a transfer tax on Form 4 transactions, currently $0 for a short rifle under 26 USC 5811.6Office of the Law Revision Counsel. 26 USC 5811 – Transfer Tax A separate making tax under 26 USC 5821 applies to Form 1 builds. The tax amount is calculated during the application process.
File electronically. ATF’s eForms system is significantly faster than paper. As of February 2026, the average processing time for an eForm 1 was 36 days, and an eForm 4 filed by an individual averaged 10 days.7Bureau of Alcohol, Tobacco, Firearms and Explosives. Current Processing Times Those averages move with application volume, and paper submissions typically take months longer.
Do not build the rifle or take possession of a transferred one before your form is approved. Possessing an unregistered NFA firearm is a federal crime under 26 USC 5861, and a pending application is not a defense.8Office of the Law Revision Counsel. 26 USC 5861 – Prohibited Acts For Form 1 builds, keep your upper and lower out of a short-rifle configuration until the stamp is in hand.
Engraving Your Form 1 Build
If you make your own short rifle, federal regulations require you to permanently mark the firearm before use. The serial number goes on the receiver. Your name (or a recognized abbreviation), city, and state go on the frame, receiver, or barrel.9Bureau of Alcohol, Tobacco, Firearms and Explosives. NFA Handbook Chapter 6 – Making NFA Firearms by Nonlicensee
The physical specifications are:
- Minimum depth of .003 inch, measured from the flat surface of the metal.
- Minimum print size of 1/16 inch for the serial number.
- Roman letters and Arabic numerals only. Hyphens are permitted.10ATF eRegulations. 27 CFR 479.102 – Identification of Firearms
Most owners send the receiver to a professional engraver. A home engraving tool can work, but markings that are too shallow or too small render the firearm improperly identified under federal regulations.
Constructive Possession: The Pre-Approval Trap
You do not need a fully assembled short rifle to be charged. Under constructive possession, owning an unregistered lower receiver alongside a short barrel and the parts to combine them can be treated as possession of an unregistered NFA firearm. Prosecutors generally need to show that you knew the parts were there and could assemble them.
The scenario that catches people is buying a 10.5-inch upper and an AR-15 lower receiver without filing a Form 1 first, intending to assemble after approval. Once those parts are in the same place and under your control, you are exposed even if they are still in separate boxes. The safe practice is to hold off on acquiring a short upper until the Form 1 is approved. If you already have the parts, file promptly and keep them physically separated. Separation is better than nothing, but it is not a guaranteed defense.
Letting Others Handle the Rifle: NFA Trusts
A short rifle registered to an individual can be possessed only by that person. Handing it to a friend at the range, or leaving it in a safe your spouse can access when you are not there, can create an unintentional federal violation. An NFA trust registers the firearm to a legal entity instead, so any named trustee can lawfully possess and use it without you being present.
The tradeoff is paperwork. Every “responsible person” on the trust, meaning anyone who can direct the management or use of trust property, has to submit fingerprints, a photograph, and a background check each time a new NFA item is added.5Bureau of Alcohol, Tobacco, Firearms and Explosives. National Firearms Act Responsible Person Questionnaire Trusts also make inheritance cleaner, letting successor trustees take over without the firearm passing through an estate process that could create a gap in legal possession. Legal fees for setting up a trust typically run $150 to $600.
Transporting a Short Rifle
Within Colorado
Colorado law exempts a person carrying a weapon in a private vehicle for lawful protection of themselves or their property from the state’s concealed-carry prohibition.11Colorado Bureau of Investigation. Colorado Revised Statutes 18-12-105 A separate statute stops cities and counties from creating their own rules for firearms in private vehicles, keeping the standard consistent across the state.12Justia Law. Colorado Code 18-12-105.6 – Limitation on Local Ordinances Regarding Firearms in Private Vehicles
Colorado concealed carry permits cover handguns. A permit does not authorize concealed carry of a short rifle on your person outside a vehicle. Local governments can still regulate open carry, so check municipal ordinances at your destination if you plan to carry a short rifle visibly outside the vehicle.13Department of Public Safety. Colorado Gun Laws
Across State Lines
Federal law prohibits transporting a short rifle across state lines without prior written authorization from ATF.14Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts You get it by submitting ATF Form 5320.20 before the trip, listing the firearm details, destination, and approximate travel dates.15Bureau of Alcohol, Tobacco, Firearms and Explosives. Application to Transport Interstate or to Temporarily Export Certain NFA Firearms The form can be filed through eForms.
Approval from ATF does not override the destination state. Several states ban short rifles outright regardless of NFA registration. Confirm the destination allows them before you leave.
Penalties If You Get It Wrong
Possessing a short rifle without valid registration is a class 5 felony in Colorado, with a presumptive prison range of one to three years, a mandatory two-year parole period, and a possible fine of $1,000 to $100,000.16Justia Law. Colorado Code 18-1.3-401 – Felonies Classified, Penalties A second conviction becomes a class 4 felony, which carries a longer prison range.1Justia Law. Colorado Code 18-12-102 – Possessing a Dangerous or Illegal Weapon
Federal charges are prosecuted separately. Anyone who possesses an unregistered NFA firearm faces up to $10,000 in fines and up to ten years in federal prison.17Office of the Law Revision Counsel. 26 USC 5871 – Penalties Federal prosecutors do pursue these cases, especially when an unregistered NFA firearm surfaces during another investigation.
Any firearm involved in an NFA violation is subject to seizure and permanent forfeiture. There is no public sale. The government either destroys the firearm or transfers it to a law enforcement agency.18Office of the Law Revision Counsel. 26 USC 5872 – Forfeitures You will not get it back and will not be compensated.
Law Enforcement and Military
Colorado provides an affirmative defense for peace officers and members of the U.S. armed forces or Colorado National Guard who possess a short rifle in the lawful discharge of their duties.1Justia Law. Colorado Code 18-12-102 – Possessing a Dangerous or Illegal Weapon That covers on-duty use and official training. It does not cover off-duty possession or personal ownership. An officer who wants a short rifle at home goes through the same NFA registration process as any other civilian.