Cap and ball revolvers appear to be illegal here in CO. In the regulations book, there is not even a mention of them, only muzzleloading rifles. You can't even use sabot bullets here in CO during muzzleloader season. It reads:
MUZZLELOADING RIFLES & SMOOTHBORE MUSKETS
a.In-line muzzleloaders are legal.
b.Must be single-barrel that fires a singleround-ball or conical projec-tile the length of which does not exceed twice the diameter.
c. To hunt deer, pronghorn or bear, they must be .40 caliber or larger.
d. To hunt elk or moose, they must be .50 caliber or larger.
e. From .40 caliber to .50 caliber, bullets must weigh at least 170 grains.
f.If greater than .50 caliber, bullets must weigh at least 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. Scopes pro-hibited. Fiber optic sights and fluorescent paints are legal. Artificial light,batteries and electronic gear are illegal.
k. Sabots are prohibitedin muzzleloading seasons. Cloth patches arenot sabots.
l. Smokeless powder prohibited in muzzleloading seasons. Blackpowder, Pyrodex (granulated, not pellets), Clear Shot, Clean Shotand Triple 7 are legal.
m.Only legal muzzleloaders allowed in muzzleloading seasons.
As for handgun regs, it must produce 550 ft/lbs. at 50 yards to be legal. Even a .357 mag has to be stout to acheive that.