OK, here is how to do it, you check the laws first, then you decide. Buy a H&R Sidekick BP rifle. Now you need to do a little machine work on the shortened frame, there is a chunk of metal cast into the bottom of the frame just behind the hinge pin you will need to remove. Then you take a H&R Shotgun barrel and cut it down like you are making any other stub barrel. You will need to shorten the underlug to match the sidekick length, do a little welding and machine work. Not too hard. The Sidekick is not covered under the gun control act because it is a muzzel loader, so you do not need to worry about anyting in those laws, this is what they say, direct from the ATF:
An antique firearm as defined in both
the GCA and NFA is exempt from all of
the provisions and restrictions contained
in both laws. Consequently, such an
antique firearm may be bought, sold,
transported, shipped, etc., without regard
to the requirements of these laws.
Under the Arms Export Control Act
certain "antique firearms" are not subject
to the import controls under that Act.
These "antique firearms" are defined as
“muzzle loading (black powder) firearms
(including any firearm with a matchlock,
flintlock, percussion cap, or similar type
of ignition system) or firearms covered
by Category I(a) established to have
been manufactured in or before 1898.”
Now just do a little work on things and off you go, remember, I may be telling you a lie, and the state goverments all have different rules, just read about what you are going to do and only believe what you know to be true your self. That being said my gun shot poorly and the grief I got from this board was just not worth enduring, so I just cut it up and was done with the science experment. Larry