Here are the rules. Rifle seasons and varmit hunting the barrel is good. the 209 system is good. Otherwise, here are the actual Idaho rules for the 09-10 season as they stand today. thanks for the info....
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 muzzleloader- only 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:
• Capable of being loaded only from the muzzle.
• 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).
• Loaded only with loose black powder, loose Pyrodex, or other loose synthetic black powder. Pelletized powders are prohibited.
• Equipped with a single or double-barrel.
• Loaded with a projectile that is within .010 inch of the bore diameter. Sabots are prohibited.
• Loaded with a patched round ball or conical non-jacketed projectile comprised wholly of lead or lead alloy.
• Equipped only with a flint, percussion cap or musket cap. 209 primers are prohibited.
• 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.