Deer hunting caliber rules in Colorado
What Colorado allows you to shoot a deer with, in plain English, taken from the state's own regulation and quoted below so you can check our reading against it.
A plain-English summary, last reviewed September 2026. Hunting law changes every year and varies by zone, season and public versus private land, and this page is not legal advice. Before you hunt, confirm the current rule with Colorado Parks and Wildlife.
The state sets a floor - a minimum caliber, bullet weight or muzzle energy - that small cartridges can fail.
The rule as Colorado writes it
Rifles must use center-fire cartridges of .24 caliber or larger with expanding bullets of at least 70 grains and a manufacturer-rated impact energy of at least 1,000 ft-lb at 100 yards; a semiautomatic rifle may hold no more than six rounds in magazine and chamber combined; handguns need a 4-inch barrel, a .24 or larger expanding bullet and 550 ft-lb at 50 yards.
Is a .223 legal for deer in Colorado?
No. Colorado writes a floor into its deer rules that the .223 and 5.56 sit under, so the cartridge is not legal for deer here even though it is legal in most states.
What is the minimum caliber for deer in Colorado?
Colorado does set a floor: a center-fire cartridge of .24 caliber or larger, firing an expanding bullet of at least 70 grains. The rule in full, including the shotgun and muzzleloader options, is quoted at the top of this page, and the regulation itself is linked in the sources.
What a caliber or energy floor means for your rifle
Here the state writes a number into the rules: a minimum caliber, a minimum bullet weight, a minimum muzzle or downrange energy, or a combination. That number is what makes a cartridge legal or illegal, and it can rule out a rifle that is perfectly legal one state over.
Energy floors are the ones people get wrong. Energy depends on the load, not the caliber, so two boxes of the same cartridge can land on opposite sides of the line. The manufacturer's ballistics table is the document that answers the question, and it is worth printing the line for the load you carry.
If your cartridge sits near the limit, the safer move is to step up rather than argue the arithmetic with a warden. Nothing in a citation improves the meat.
Caliber is the smallest part of a clean kill. Work out what your cartridge carries at the range you hunt with the cartridge and energy guide or the cartridge comparison tool, then put the shot where it counts.
States with the same kind of rule
The state sets a floor - a minimum caliber, bullet weight or muzzle energy - that small cartridges can fail.
The full picture is in the 50-state deer caliber table, and the regulations hub has the agency directory and a pre-hunt legal checklist.
Sources
We read this state's rule from the source below in September 2026 and quoted it above:
- Colorado Parks and Wildlife, Chapter W-2 Big Game, #203 (as approved November 2025)
- Colorado Parks and Wildlife - the agency that publishes and enforces it.
Rules are summarised for orientation and change often; the official regulation linked above is the authority. Zones, seasons and local ordinances can add to the statewide rule: the regulations hub has the pre-hunt legal checklist.
Range-day gear, whatever your state allows
The rule quoted above tells you what is legal; these are the tools that make any legal setup accurate enough to matter.
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