Yes, you can own an AR-15 in Colorado. The rifle itself is legal under state law, but the configuration you buy and the city you live in both shape what’s actually lawful. Statewide, magazines are capped at 15 rounds. Several municipalities, including Denver and Boulder, ban the platform entirely. And every buyer must be at least 21, clear a background check, and wait three days before taking the rifle home.
The 15-Round Magazine Cap
The biggest statewide restriction on the AR-15 isn’t aimed at the rifle. It’s aimed at the magazine. Colorado makes it a criminal offense to sell, transfer, or possess a magazine that holds more than 15 rounds.1Justia Law. Colorado Code 18-12-302 – Large-Capacity Magazines Prohibited – Penalties – Exceptions Standard AR-15 magazines ship with 30-round capacity, so a factory-standard mag is illegal to buy, sell, or possess in the state unless it was grandfathered.
The grandfather clause lets you keep a magazine over 15 rounds if you owned it in Colorado before July 1, 2013, and have kept continuous possession since. Continuous possession is strict: you can’t lend it, sell it, or give it away. The moment a grandfathered magazine changes hands, the exemption dies and the new holder is in violation.1Justia Law. Colorado Code 18-12-302 – Large-Capacity Magazines Prohibited – Penalties – Exceptions
Buy a new AR-15 from a Colorado retailer and it comes with a 15-round magazine or smaller. Violating the cap is a class 2 misdemeanor, punishable by up to 120 days in jail, a fine of up to $750, or both.1Justia Law. Colorado Code 18-12-302 – Large-Capacity Magazines Prohibited – Penalties – Exceptions
Cities That Ban the AR-15 Outright
In 2021, Colorado declared firearm regulation a matter of both state and local concern, which gave cities and counties the power to enact rules stricter than state law.2Colorado General Assembly. SB21-256 Local Regulation Of Firearms Denver, the City of Boulder, and Boulder County have all used that authority to prohibit what their codes call “assault weapons,” and a standard AR-15 falls inside those definitions.
The local ordinances use a feature-based test. A rifle that has characteristics like a pistol grip, a folding or telescoping stock, and the ability to accept a detachable magazine qualifies as an assault weapon regardless of what magazine is loaded. That means selling, purchasing, or possessing an AR-15 within those jurisdictions is banned.
Some of these ordinances are still being litigated. As of mid-2025, a federal judge allowed part of a challenge to Boulder County’s ordinance to proceed, permitting plaintiffs to contest the prohibition on future possession while finding challenges to bans on current possession were not viable. The bans are being enforced during the litigation. If you live in or travel through a city with an assault weapon ban, check the local code before bringing an AR-15 in.
Buying an AR-15 in Colorado
You Must Be 21
Colorado’s minimum age to purchase any firearm, including long guns like the AR-15, is 21. The law was enacted in 2023 and applies to both dealer and private sales.3Colorado General Assembly. SB23-169 Increasing Minimum Age To Purchase Firearms Active-duty military and law enforcement are exempt. The Tenth Circuit upheld the law against a Second Amendment challenge in late 2024, and a federal district court reaffirmed it in 2025.
Background Check on Every Sale
Every firearm transfer in Colorado runs through a federally licensed dealer, including private sales between friends or family. The seller who isn’t a licensed dealer has to arrange for an FFL to run the check before the transfer.4Justia Law. Colorado Code 18-12-112 – Private Firearms Transfers – Sale and Purchase – Background Check Required – Penalty – Definitions The dealer contacts the Colorado Bureau of Investigation’s InstaCheck unit, which as of March 2025 charges $15 per check.5Colorado Bureau of Investigation. InstaCheck The dealer also charges a separate transfer fee, typically $20 to $75.
Three-Day Waiting Period
You wait three days after the background check is initiated, or until the check is approved, whichever comes later.6Colorado General Assembly. Waiting Period To Deliver A Firearm If the check clears in a day, you still wait three. If it takes five days, you wait five. A dealer who releases a firearm early faces a $500 fine on a first offense and up to $5,000 for subsequent violations.7Colorado Department of Public Health and Environment. Obtaining, Possessing and Selling Firearms – Section: Waiting Periods
Who Can’t Own One
Anyone convicted of a felony under Colorado, federal, or another state’s law is barred from possessing any firearm. Possession by a felon is itself a class 6 felony, and it steps up to class 5 or class 4 depending on the weapon involved and whether the prior offense was violent.8Justia Law. Colorado Code 18-12-108 – Possession of Weapons by Previous Offenders
Certain misdemeanor convictions in the previous five years also disqualify you. The list includes third-degree assault, unlawful sexual contact, child abuse, some protection-order violations, harassment, bias-motivated crimes, certain cruelty-to-animals offenses, and crimes against at-risk persons. The CBI will deny the transfer even if you’d otherwise pass the federal check.
The Marijuana Trap
This one catches Colorado residents off guard. Marijuana is legal under state law, but it remains a Schedule I controlled substance under federal law, and federal firearms law prohibits any unlawful user of a controlled substance from possessing a gun.9Office of the Law Revision Counsel. 18 U.S. Code 922 – Unlawful Acts Question 21(e) on ATF Form 4473 asks whether you’re an unlawful user of marijuana or any other controlled substance. Answering “no” while holding a medical marijuana card or using regularly creates a federal perjury risk. Colorado passed legislation trying to protect medical cardholders at the state level, but the federal prohibition still applies and the ATF still enforces it.
Storing, Transporting, and Reporting
Secure Storage
Colorado requires firearms to be stored so unsupervised minors and other unauthorized users can’t get to them. Responsible storage means the firearm is on your person, within arm’s reach, locked in a gun safe, or secured with a trigger or cable lock.10Colorado Department of Public Health and Environment. Firearms Safe Storage Requirements Propping an AR-15 in a closet does not meet the standard. Unlawful storage is a class 2 misdemeanor. Providing a handgun to a juvenile is a class 4 felony.
In the Vehicle
Any rifle or shotgun in a motor vehicle must have an unloaded chamber. The rule comes from the wildlife code but applies year-round, not just during hunting season, and a peace officer can inspect the chamber of any long gun in your vehicle.11Department of Public Safety. Colorado Gun Laws Handguns are exempt from that particular statute; the AR-15 is not. The statute doesn’t require a case, but a locked case in the trunk or cargo area clearly demonstrates the rifle isn’t readily accessible. If your route passes through a city with an assault weapon ban, keep it cased, unloaded, and out of reach.
Lost or Stolen
Report a lost or stolen firearm to local law enforcement within five days of discovering the loss. Include the manufacturer, model, serial number, caliber, and any identifying marks. A household member can file for you. Failing to report is a $25 civil infraction on a first offense; a repeat failure is an unclassified misdemeanor punishable by up to $500.12Justia Law. Colorado Code 18-12-113 – Failure to Report a Lost or Stolen Firearm – Exception
Places You Can’t Bring It
A lawfully owned AR-15 still can’t go everywhere. Colorado prohibits firearms in:13Justia Law. Colorado Code 18-12-105.5 – Unlawfully Carrying a Firearm in a Place Where Prohibited
- Courthouses and buildings used for court proceedings
- Public and private K-12 campuses and universities
- Licensed childcare centers
- State legislative buildings, including chambers, galleries, offices, and committee hearing rooms
- Public buildings with permanent security screening at every entrance
- Public transportation facilities, for loaded firearms
- Polling locations and ballot drop boxes during elections, including within 100 feet of a drop box or the building housing a polling location or count facility
Local governments can designate additional prohibited areas, including government buildings within their jurisdictions. Carrying into a prohibited location can bring criminal charges no matter what permits you hold.