BCsteve
WKR
Like everyone said. Deep socket, wooden dowel, pvc pipe wrapped in sandpaper. Go back and forth in the channel until if fits. Did this many times with different stocks. Did it with a Tikka camo stock just a couple weeks ago for my .35 Whelen which has a barrel contour probably similar to D18. Another method that I used to finish was to tape your barrel for protection and slip a strip of sandpaper between the barrel and stock and pull back and forth so you're sanding following the contour of the barrel. Works great.
