Colorado’s assault rifle laws do not ban semi-automatic rifles at the state level, including AR-15-platform firearms, but they layer age limits, background checks, waiting periods, magazine caps, accessory bans, and storage rules on top of ownership. Since 2021, cities and counties have also had the authority to pass their own bans on firearms the state still allows. What’s legal on one side of a city line can be a criminal offense on the other.
What Colorado Bans Outright
Standard semi-automatic rifles are legal to buy, own, and sell in Colorado if you meet the age and background-check requirements. There is no state feature test and no state list of banned models.
The state does prohibit a narrower category of firearms as “dangerous weapons” under C.R.S. § 18-12-102: machine guns, machine-gun conversion devices, firearm silencers, short shotguns, and short rifles. Possession is a class 5 felony.1FindLaw. Colorado Code 18-12-102 – Possessing a Dangerous or Illegal Weapon A “short rifle” is any rifle with a barrel under sixteen inches or an overall length under twenty-six inches.2Justia. Colorado Code 18-12-101 – Peace Officer Affirmative Defense – Definitions
You can own a short-barreled rifle legally, but only through the federal National Firearms Act. As of January 2026, the federal tax stamp fee dropped to $0, but the registration process still applies. You file ATF Form 1 to build one yourself or Form 4 to buy one, submit fingerprints, pass the NFA background check, wait for ATF approval before taking possession, and engrave the lower receiver with your name, city, state, and caliber. Skipping registration exposes you to federal and state felony charges.
Local Bans That Override the State Baseline
SB21-256 repealed Colorado’s firearm preemption law in 2021. Local governments can now pass gun regulations stricter than state law, as long as they are not less restrictive than the state baseline.3Colorado General Assembly. SB21-256 Local Regulation of Firearms
Denver has banned assault weapons since 1989. The city’s ordinance targets semi-automatic centerfire rifles with a detachable magazine holding twenty-one or more rounds, semi-automatic shotguns with a folding stock or magazine capacity over six rounds, and parts or kits designed to convert a firearm into a prohibited configuration. Denver also caps magazine capacity at twenty rounds, stricter than the state’s fifteen. Violating the ordinance carries a fine of $100 to $999, a jail sentence of ten to 180 days, and confiscation and destruction of the weapon. Boulder and Vail have enacted their own restrictions. A federal lawsuit filed in 2026 challenges Denver’s ban on Second Amendment grounds, so the status of these ordinances may change.
Because enforcement follows city and county lines, you need to check local ordinances for every jurisdiction you pass through with a rifle. Ignorance of a municipal ban is not a defense.
Magazine Capacity Limit
Colorado bans large-capacity magazines statewide, defined as any fixed or detachable magazine that accepts more than fifteen rounds.4Justia. Colorado Code 18-12-301 – Definitions Since July 1, 2013, selling, transferring, or possessing one has been illegal unless you owned it before that date and have maintained continuous possession.5Colorado Bureau of Investigation. Colorado Code 18-12-302 – Large-Capacity Magazines Prohibited
Penalties escalate:
- First offense: class 2 misdemeanor, up to 120 days in jail and a fine up to $750.5Colorado Bureau of Investigation. Colorado Code 18-12-302 – Large-Capacity Magazines Prohibited6Justia. Colorado Code 18-1.3-501 – Misdemeanors Classified – Penalties
- Second or subsequent offense: class 1 misdemeanor, up to 364 days in jail and a fine up to $1,000.6Justia. Colorado Code 18-1.3-501 – Misdemeanors Classified – Penalties
- Possession during a felony or crime of violence: class 6 felony.5Colorado Bureau of Investigation. Colorado Code 18-12-302 – Large-Capacity Magazines Prohibited
If you claim grandfather protection, the prosecution carries the burden of disproving it. Proving continuous possession of a magazine bought years ago without a receipt is harder than it sounds. The restriction applies to the magazine itself regardless of which firearm it fits.
Rapid-Fire Trigger Activators
Colorado prohibits possessing, selling, or manufacturing rapid-fire trigger activators, including bump stocks and binary triggers. HB24-1292 addressed weapons and accessories used in mass shootings.7Colorado General Assembly. HB24-1292 Prohibit Certain Weapons Used in Mass Shootings
The state ban stands independently of federal law. When the U.S. Supreme Court decided Garland v. Cargill in 2024, it struck down the federal ATF rule that classified bump stocks as machine guns, holding that bump stocks do not fire more than one shot “by a single function of the trigger.” That ruling removed the federal prohibition, not the state one. A first violation in Colorado is a misdemeanor with potential jail time.
Buying a Rifle
You Must Be 21
Since 2023, you must be at least twenty-one years old to purchase any firearm in Colorado, including long guns. SB23-169 raised the age from eighteen and applies to both licensed dealers and private sellers. The exceptions are active-duty members of the U.S. armed forces and peace officers certified by the P.O.S.T. board. Buying while under twenty-one is a class 2 misdemeanor, and facilitating the sale as a dealer is too.8Colorado General Assembly. SB23-169 Increasing Minimum Age to Purchase Firearms
Background Checks on Every Transfer
Every firearm transfer in Colorado, dealer or private, requires a background check processed by the Colorado Bureau of Investigation’s InstaCheck unit. The seller cannot hand over the firearm until CBI returns an approval. The fee is $15.00 as of March 2025.9Colorado Bureau of Investigation. InstaCheck
Private sellers who skip the check face a class 2 misdemeanor conviction and a two-year prohibition on possessing any firearm from the date of conviction.10Justia. Colorado Code 18-12-112 – Private Firearms Transfers – Background Check Required – Penalty That ban gets reported to CBI and the national system, so it follows you across state lines.
Three-Day Waiting Period
HB23-1219 requires a waiting period on all firearm deliveries. The seller cannot release the firearm until the later of two events: three days after the background check was initiated, or when CBI actually approves the transfer.11Justia. Colorado Code 18-12-115 – Waiting Period – Penalty If CBI takes longer than three days, you wait until they approve.
Delivering early is a civil infraction. A first violation carries a $500 fine; a subsequent violation runs $500 to $5,000.11Justia. Colorado Code 18-12-115 – Waiting Period – Penalty Exceptions apply to antique firearms, curios and relics, and transfers to family members by military personnel deploying within thirty days.
Serial Numbers and Ghost Guns
SB23-279 took effect on January 1, 2024. Possessing, transporting, selling, or purchasing a firearm, frame, or receiver without a serial number is illegal. The law also prohibits unfinished frames or receivers unless they have been serialized as required by federal law. Anyone who built an unserialized firearm before the law had until January 1, 2024 to get it serialized by a federally licensed manufacturer.12Colorado General Assembly. SB23-279 Unserialized Firearms and Firearm Components
A first offense is a class 1 misdemeanor, up to 364 days in jail and a $1,000 fine. A second offense is a class 5 felony with one to three years in prison. A felony conviction triggers a permanent firearm-possession ban, and even the misdemeanor bars you from purchasing a firearm for five years through the CBI background check.12Colorado General Assembly. SB23-279 Unserialized Firearms and Firearm Components
Safe Storage
Colorado requires firearms to be securely stored when not in use to prevent access by unsupervised juveniles and other unauthorized users under C.R.S. § 18-12-114. Failing to store responsibly is a class 2 misdemeanor, up to 120 days in jail and a fine up to $750.13Colorado Department of Public Health and Environment. Firearms Safe Storage Requirements
Related statutes get heavier when a minor actually accesses the firearm. Providing a handgun to a juvenile, or letting one possess it, is a class 4 felony. Providing a rifle or other non-handgun to a juvenile is a class 1 misdemeanor.13Colorado Department of Public Health and Environment. Firearms Safe Storage Requirements
Transporting a Rifle
Colorado does not ban open carry of long guns at the state level, but it does not protect it either. Open carry is regulated locally by counties and municipalities, so whether you can carry a slung rifle in public depends on where you are.14Colorado Department of Public Safety. Colorado Gun Laws
In a vehicle, any long gun must have an unloaded chamber. A loaded magazine can be in the firearm as long as no round is chambered.14Colorado Department of Public Safety. Colorado Gun Laws Clearing the chamber before putting a rifle in a vehicle keeps you compliant statewide.
Local assault weapons bans apply while you travel. If your rifle or magazine configuration violates a municipal ordinance, driving through that jurisdiction with the firearm in your vehicle can trigger enforcement.
Marijuana and Federal Prohibited-Person Status
Colorado legalized recreational marijuana, but federal law still classifies it as a controlled substance. Under federal firearm regulations, anyone who uses marijuana, whether through a state medical card or a recreational purchase, is a prohibited person who cannot lawfully possess firearms or ammunition. ATF Form 4473, which every buyer signs at purchase, asks whether you are an unlawful user of a controlled substance, and marijuana use makes the answer “yes” under federal standards regardless of state legality.
A draft ATF form under review suggests that if marijuana is federally rescheduled, state-authorized medical cannabis patients might no longer be treated as unlawful users for firearm purposes. Until that change takes effect, the prohibition stands.