What Calibers Are Legal for Deer Hunting in Missouri?

The legal calibers for deer hunting in Missouri are broader than many hunters assume: any centerfire rifle or handgun cartridge is allowed during the firearms season, with no minimum bore size, as long as the ammunition uses expanding projectiles. Shotguns firing single slugs, muzzleloaders of at least .40 caliber, and big-bore air guns of at least .40 caliber are also legal, each with their own conditions. The governing rule is 3 CSR 10-7.431 of the Missouri Wildlife Code.¹

Centerfire Rifles and Handguns

Missouri sets no minimum caliber for centerfire rifles or handguns used during the firearms deer season. A .223 Remington is as legal as a .30-06, provided the bullets expand on impact. That puts the state apart from jurisdictions that mandate a minimum bore diameter or cartridge length.¹

The real gatekeeper is the ammunition. Full hard metal case projectiles, commonly sold as full metal jacket or FMJ, are explicitly prohibited. Soft-point, hollow-point, and ballistic-tip bullets all qualify as expanding types and are the standard choices for whitetail. The round must also propel only one projectile per discharge, which matters more for shotgun loads than for rifle ammunition.

“Centerfire” means the firing pin strikes a primer in the center of the cartridge base. That covers nearly all modern rifle and handgun ammunition above .22 caliber.¹

Shotguns

Shotguns are legal during the firearms portion of the season. The limiting factor is the single-projectile rule: slugs only, no buckshot. Any load that fires more than one projectile per discharge is prohibited for deer, and full hard metal case projectiles are banned regardless of the platform.¹

Rifled slug barrels and sabot slugs have made shotguns genuinely accurate out to 150 yards or more, which keeps a 12- or 20-gauge in play for timber and farmland hunters.

Muzzleloaders

Missouri runs a dedicated muzzleloader portion of the deer season. During that window, only muzzleloading firearms with a bore diameter of .40 caliber or larger are permitted. Cap-and-ball handguns face the same .40-caliber floor. The powder and projectile must be loaded from the muzzle end of the barrel.¹

Flintlock, percussion cap, and modern 209 shotgun primer ignition systems are all accepted. Muzzleloaders are also legal during the firearms “any legal method” portion, so a front-stuffer isn’t locked to the muzzleloader-only window.

Air Guns

Big-bore air guns are legal for deer in Missouri if they meet two conditions: a minimum caliber of .40 and an external high-compression power source such as a hand pump, separate air tank, or air compressor. Spring-piston guns, CO2 cartridge guns, and small-caliber pellet rifles do not qualify.¹

Pre-charged pneumatic rifles in .45 and .50 caliber are typical choices. A .177 or .22 pellet rifle is nowhere close to legal for deer no matter how much pressure it generates. Air guns are permitted under the “any legal method” season rather than the dedicated muzzleloader portion.

What’s Prohibited

The banned list is short and strictly enforced:

Rimfire cartridges, including .22 Long Rifle and .17 HMR.
Full hard metal case projectiles (FMJ and similar non-expanding bullets).
Multi-projectile ammunition, including buckshot.
Fully automatic firearms, for any hunting activity.
Electronically activated calling devices.
Methods restricted by local ordinance.

Every item on that list comes directly from the Wildlife Code.¹

Magazine Capacity for Semi-Autos

Self-loading firearms used for deer hunting cannot hold more than eleven total cartridges in the magazine and chamber combined. In practice that’s ten in the magazine plus one chambered. Concealable firearms as defined in Chapter 571 of Missouri’s revised statutes are exempt from the capacity limit, but a concealable firearm carried under that exemption cannot be used to take wildlife while deer hunting. The exemption is a self-defense allowance, not a hunting workaround.¹

Bolt-action, lever-action, and single-shot rifles aren’t affected. If you hunt with a semi-automatic, confirm your magazine capacity before opening day. Aftermarket ten-round magazines are widely available for most popular platforms.

Blaze Orange Is Required Alongside Your Firearm

During the firearms deer season and managed firearms deer hunts, every person hunting any game, plus any adult mentor accompanying a hunter, must wear a cap or hat and a shirt, vest, or coat in blaze orange that is visible from all sides. Camouflage-pattern orange does not satisfy the rule.¹

Exemptions include archery permit holders during the alternative methods portion, migratory bird hunters, hunters in counties closed during the antlerless and CWD portions, and archery hunters inside municipal boundaries where firearm discharge is already prohibited.

Local Ordinances Can Narrow State Rules

A caliber and firearm combination that passes muster under the Wildlife Code can still be illegal where you plan to hunt. The regulation lists “methods restricted by local ordinance” among the prohibited categories.¹ Some municipalities and counties prohibit rifle-caliber discharge within their boundaries or limit hunting to shotguns and archery. Check the rules for the specific county or city before the season, and call the local conservation agent if you’re unsure.

1
Justia Law. Missouri Code of State Regulations 3 CSR 10-7.431