Stretchman, I bought a .69 cal., straight taper, from Oregon barrel company. Its my next project. Nice folks to work with. Prior to this, the biggest gun I had made was a 12 ga. fowler, that I shoot shot, and round ball from. Based on that gun, I know one thing at least. Architecture is everything! If you want a pleasant, (relatively) shooting gun, you have to get that right. A wide flat butt plate is a must. I would suggest looking at Jaeger, and English Sporting rifles to get an idea what I mean, also TOW sells plans for English Sporting rifles, they are fairly inexpensive, you don't have to copy them exactly, but the architecture is tried and true. Good luck!
Robby