Griz,
Since you know that I most often make my own barrels, I cannot use the precarved stocks and must hand inlet the swamped barrels.
How I do it is to cut the wood down to the level of the barrel centerline, leaving the breech end "hump" high and square. I have two rods, each 1/2 inch square and about a foot longer than the barrel. I have drilled a lot of holes through the rods to fit #8 screws all along the length of the rods. I lay the barrel with the rods on each side on the wood surface. Using a bunch of C-clamps I clamp the rods to flex and fit tightly against the sides of the swamped barrel. Next I drill down through the existing holes and install the #8 screws tight. The holes are offset in the rod to allow for the thickness of the finished forestock, and none are installed where the lock panels are (the wood would be too thick here and the #8 screws would cut into this thickness). With the rods tightly screwed to the wood, I remove all the clamps and the barrel. This leaves the rods on the wood at the exact shape of the swamp curve. This gives an excellent guide for chiseling out the barrel channel.
I actually use a modified backsaw to cut the channel exactly along the curved rods. You can really inlet a swamped barrel air tight this way. The job can be completed in a few hours. If you guys can wait until late May when I return to the USA, I can lend you the rods & modified saw.
Jim