Hey Whitebear
While I no longer inlet long barrels by hand (Dave Rase does that for me), I still do every pistol barrel by hand, most of which have been oct-round or full round. My method for starting is much like Gunmaker - I measure just over half depth in the stock, maybe 1/16" deeper than center, and draw that profile on the side of the stock. I set up my drill press (little bench top model from the 80s, cost 25 bucks on craigslist, worth every cent), and set the depth stop where the line is at the breech. Drill the hole with a 3/8 to 1/2" bit, then move it over, set the depth, drill the next hole, etc. It takes a little while, but you can usually drill 5-10 holes without adjusting the depth stop. Go the whole length of the channel and when you're done chisel out the wood in between - you'll now be within a few scraper passes of an accurate bottom profile. I lay the barrel on top of that groove, then roughly trace the sides onto the wood - next cut to within 1/8" or so of the lines with a gouge, then you can draw more accurate lines as the barrel drops in. The last 32" or so is done with scrapers and lamp soot. It goes surprisingly quickly once you get past the drilling part.
As for cast off - I use between 1/8 and 3/16 on every gun I build. On one earlier one I did (that is my regular shooter) I used about 5/16, too much, but still comfortable in the smaller caliber that it is. If you haven't built one with cast off, its well worth your effort to try it! Good luck,
-Eric
