CU,
Making a rifling machine is fairly simple with the basic parts being a pair of breaings, a rack and pinion gear (McMaster-carr del.'s next day) and a piece of shafting. Mine is much like the one GG linked to.Making the machine was the easy part. The more guarded secret is the how to, do's and dont's.
GG is right about the tool pressure on the larger radiused grooves like that of the 3 groove Parrott rifles. This would be difficult (depending on size, .5 ok 3.0 no way ) to do without some heavy duty eqp at home..There were many styles of rifling used in the Civil War.; everything from 1/8 wide poly grooves to the 15 x15 that I built would be easy to cut. Choose wisely.
The spring loaded hook style cutter body takes a little time but are not hard to make. I have not tried to do a blind hole of a muzzle loader yet because My interest has been more to the obscure civil war breech-loaders. I am not so sure but I think that I would make a liner and insert it. Sooner or later I will get there and find out.
IF you have thought about rifling something for very long give it a try. If you look in the right places you should be able to make a machine for around a $100. (manual).
RCHJr.