Sorry handirifle, but I don't have a barrel for you even though I am fairly eccentric myself (The more grey the greater the entitlement) As barrels go, it won't matter if it was a rifle barrel, the regulation is on the reciever or frame, or most legally, that part which is engraved with the serial number.
I can't take my Springfeild 120A (an old bolt action single shot 22LR) and make a pistol from it. Nothig would prevent me from taking he barrel off, cutting it down and installing it on a Ruger MKII frame, I can even leave the barrel it's full length, (20") on the Ruger frame, I just can't make a pistol from a rifle. Go figure. Strikes me that a 20" handgun is infinately more concealable than a short rifle, but my short rifle must be 26" OAL if I remember correctly, and must have a barrel of 16". It is obvious tht politicians figured this crap out.