Well I am not positive on the barrel length but here is the rule in the 2012 regs.
.
e. A muzzleloading handgun must have a
single or double barrel of at least eight
inches, must be rifled, and must be
capable of being loaded with fortyfive
grains or more of black powder
or black powder substitute per the
manufacturer's recommendations.
f. A muzzleloading handgun used for big
game must be .45 caliber or larger.
g. A handgun designed to be used with
black powder, including black powder
percussion revolvers, can be used to
hunt forest grouse, cottontail rabbits,
and snowshoe hares.
