On Don's point about modern guns, I recently had to disperse a widow's collection of various guns (no sxs's, unfortunately). One gun in the bunch was a sawed off 870 Rem. It was very used and abuse looking. But what caught my eye was the eccentric bore/wall. At about 18 1/2" long, the wall was pretty thick. But it was in the area of .035 on one side and maybe an 1/8" on the other.