It doesn't take much, maybe .020 the length of the bolster. You can file the back end of the bolster down this much then file it flat to the front. Another way is to solder a thin steel wedge on the bolster. You can file it out of a hacksaw blade, which is about .023 thick. You can draw your lock and panels to scale in a top view looking down on the lock and the panels. Lay out the taper you want, then measure the amount the bolster will have to taper. My .58 flint plains rifle has a 31" tapered barrel, 1.125 at rear and 1.020 at the muzzle. The panels are 6.5" long. Across the front they measure 1.792 in width and 1.500 at the rear.
Other rifles, 6.25" lock panels, 1 1/8" barrel has 1.75 across the front and 1.625 across the rear. A 1" barrel was 1.625 at front and 1.500 at rear.
My Bridger Hawken has a 1 1/8" barrel, 6.25" lock panels. It is 1.755 at front and 1.560 at rear. Carl Walker of the old GRRW told me the original Bridger Hawken had its lock plate bent to lower the tail of the lock for the tapering panels. The reason the panels are narrower across the wrist than ahead of the lock is to make a narrower wrist. A reversed taper would make a bulky wrist.
