Here's Idaho;
Muzzleloader Caliber Requirements
In any hunt, including general any-weapon seasons and shortrange
hunts, it is unlawful to pursue or kill big game animals:
Ӣ With any muzzleloading rifle or musket that is less than
.45 caliber for deer, pronghorn, or mountain lion; or
is less than .50 caliber for elk, moose, bighorn sheep,
mountain goat or black bear.
Muzzleloader-Only Season
Any person hunting in a muzzleloader-only season, including
controlled hunts, must have in their possession a license with
a muzzleloader permit validation. During a muzzleloaderonly
season, it is illegal to pursue or kill a big game animal
with any firearm, muzzleloading pistol, or weapon other
than a muzzleloading rifle or musket. In addition, the
muzzleloading rifle or musket must be:
Ӣ Capable of being loaded only from the muzzle.
Ӣ Equipped with only open or peep sights. Scopes and any
electronics are prohibited. Except hunters with a visual
disability may apply for a permit to use nonmagnifying
scopes. (Applications are available at Fish and Game
offices).
Ӣ Loaded only with loose black powder, loose Pyrodex, or
other loose synthetic black powder. Pelletized powders
are prohibited.
Ӣ Equipped with a single or double-barrel.
Ӣ Loaded with a projectile that is within .010 inch of the
bore diameter. Sabots are prohibited.
Ӣ Loaded with a patched round ball or conical non-jacketed
projectile comprised wholly of lead or lead alloy.
Ӣ Equipped only with a flint, percussion cap or musket cap.
209 primers are prohibited.
Ӣ Equipped with an ignition system in which any portion
of the cap is exposed or visible when the weapon is
cocked and ready to fire.