Marc-N-Tomtom;
I did something similar, but cut the barrel channel before taking the strip off the top that runs from the breech, to the muzzle. My rails capture the entire base of the router. The first bit for this operation, I made out of a spade bit, the same dimensions as the barrel across the flats. I later bought some barrel inletting bits, that are carbide. The big advantage to this system, is you cut the entire barrel channel with the router. Hard maple take at least three passes, sometimes more. I attached mine to a Workmate portable work bench with big C-clamps. This system allows you to adjust the tracks to cut a channel that creates cast off in the stock as well. I also use it to cut the ramrod channel in the front end of the stock.
Now if I could just make a bit that would cut a channel for a swamped barrel I'd be all set.
Hungry Horse