Contour
For a 40x the barrel will need to be at least 1.2 in dia I usually use 1.25. On a shillen i use #7 or there rimfire taper, accuracy wise it does'nt matter. On a broughton not sure of contour # it starts out 1.25 for 3 inches then tapers to .9 and runs to end that size.Dan Killough has Shillens and Harts in stock,and Charlie Scott has Broughton and Shillens between the two you should be able to find what your looking for.