Here are the Colorado laws regarding muzzleloaders!
MUZZLELOADING RIFLES & SMOOTHBORE MUSKETS
a. In-line muzzleloaders are legal.
b. Must be single-barrel that fires a single round-ball or conical projectile
the length of which does not exceed twice the diameter.
c. To hunt deer, pronghorn or bear, they must be min. of .40 caliber.
d. To hunt elk or moose, they must be min. of .50 caliber.
e. From .40 caliber to .50 caliber, bullets must weigh min. 170 grains.
f. If greater than .50 caliber, bullets must weigh min. 210 grains.
g. Shotshell primers are legal.
h. Pelletized powder systems prohibited in muzzleloading seasons.
i. Cannot be loaded from the breech in muzzleloading seasons.
j. Only open or iron sights allowed in muzzleloading seasons.
Fiber optics and fluorescent paint incorporated into or on open or iron sights are legal.
Scopes or any sighting device using artificial light, batteries and electronic
gear are prohibited during muzzleloading seasons.
k. Sabots are prohibited in muzzleloading seasons. Cloth patches are
l. Smokeless powder prohibited in muzzleloading seasons. Black
powder and black powder substitutes are legal.
m. Only legal muzzleloaders allowed in muzzleloading seasons.
n. NEW FOR 2008: Electronic or battery-powered devices cannot
be incorporated into or attached to muzzleloader during muzzleloading