Hopefully, you're kidding about making a pistol out of it. It is a blackpowder and not subject to most firearms laws that apply to modern weapons, but some places will still try to nail you on local sawed-off rifle laws. Once more, some friendly advice:
Altering firearms like sawing barrels, converting rifles to pistols, putting shoulder stocks on pistols, etc., etc. is a good way to go to jail. These are felonies is most cases, sometimes federal charges are applied. Some people have gotten themselves into deep excrement thinking they could slap a pistol upper on their AR-15 lower and just remove the buttstock. Best not to get into the practice of hacksaw gun conversions, even with muzzleloaders.
By the way, there's a great place to play with stuff that goes boom and rig stuff up to go kablooey. They're called United States Army Combat Engineers. Or if firearms are your shtick, do what I did. Go into the U.S. Army as a 45Bravo (Small Arms Repairer.) You'll train at the U.S. Army Ordnance Center and School at the charming Aberdeen Proving Grounds. After training, you'll be repairing all small arms in whatever dump the army sends you to. Eventually, you will be so sick of light machine guns, you'll be seeing them in your dreams. Like counting sheep, but I was seeing M-60s jumping over fences. It took me five years to finally forget the National Stock Number for the M-16A1 firing pin.
