Thanks BS2 and 30338.
I actually only tapered an existing part. The ribs I got from either Track of the Wolf or picked up at the nationals at Friendship Indiana.
Buy a flat bottomed rib that is as wide as the barrel at the juncture of the nose cap. (not at the muzzle. Too wide can be dealt with later. Too narrow can't be made to grow no matter how much you water it)
Measure the barrel at 3" increments and see the taper. Understand that it's tapered at the top and bottom both, so to match the taper you need to cut the reduction measurement in half If as an example your barrel tapers .014 every 3 inches you will need to taper the rib .007 every 3 inches. So take a file edge and make a slot carefully so you can measure with a depth gauge and make that each slot gets (in the case of this example) .007" deeper then the last one, starting at the muzzle end and deepening every 3" measurement all the way back to the place the rib touches the nose cap
Once you have all the depth slots made you need only draw-file the metal in-between away. A course cross-cut metal file is best to use. Get within about .001 or .002 of each slot but done file them away yet. When the bottom of the rib is very close to the depth of each slot you can then switch to a standard mill file and draw file the rest until all depth slots are gone. and you have a smooth flat bottom. Next you clamp the rib on and you'll see the muzzle end is now too wide, (as stated when I started the explanation) so scribe a line on it's bottom with a bent steel pick and unclamp it. File off the overhang to a point you file off the scribe lines. That takes very little time or effort, and is fast.
When you are done the rib will be in parallel with the bore and fits the barrel like it grew there.
At that point you can attach it with screws or solder (I like solder)