Hi David,
You can look at one I did on page two of this forum,Jim Chambers English Sporting Rifle.
The very first thing I would do is inspect the butt plate's overall condition. Look at it from different directions looking for any twists or bends. Check that the finial is not twisted, so when the butt plate is vertical the finial is Horizonte. See that the butt plate has a nice curve that pretty much match on bothe sides. File a flat on both inside edges of the butt plate. File both at the same time with the file bridging the butt plate. Aim for about a 3/16 flat. Then I would turn my attention to the tang or finial. I would draw a line on the finial from the center of the heel to the very end of the finial. The photo that you show is not very sharp so it is not possible to see what the contour looks like. If the contour of the finial is what you like clean the contour with small files...needle files if you have 'em. When you have the contour of the finial as you like file a bevel or draft so the inletting will be easier. Onto the stock. The comb and curve of the stock should be worked to the point where the drop at the heel and trigger pull is were you want. Establish a center line from the nose of the comb to the toe of the butt. If the butt plate has a small radius on the inside were the tang meets the butt plate proper, rasp a bit of wood away to move the BP forward a bit. Now comes the fun...set the finial tip center line on the center line on the comb scribe with a sharp pointed blade like an exactoknife all along the finial keeping the blade angled in towards the center . Remove the BP and slowly and deliberately deepen that line with you knife. Then from the inside carve or pare down some of the wood right to the incised line. Now you can smoke or blue the inside of the finial Prussian blue oil paint. Don't use a lot! Please the BP and finial up to the center lines and give it a light tap with a mallet. Just keep shaving off the spots on the wood that have the blue on it. Use the smallest chisels you have and take your time. My BP took the better part of a day. I'm sure you know a lot of what I wrote but some one of less experience than you may get some help from this. This takes patience and it will tax your skill.
Best of luck. Richard
PS inlet the finial straight down. When the metal is flush with the wood I put my BP heel screw in the I start to fit the butt end the normal way.
