I read this to mean that the relief at the muzzle, in the author/gun maker's experience, reduced the "blown pattern" effect by reducing pressure and "easing" the shot out of the muzzle, thus improving the shot count in relation to a similar bore-size and length barrel without relief at the muzzle. Fowling piece barrels were quite long at the time, four foot and more, and the burning characteristics of the black powder often depended on luck of the draw vis a vis source of supply. And if you think about it, constricting the muzzle would have made loading more difficult in the days before breechloaders
AHHHH, For me the lights just came on!
EDM, I think you just hit the nail right on the head!
I and others were trying to rationalize how opening a muzzle could tighten "normal" patterns, they probably weren't normal, they were actually "blown". AHH, I see said the blind man.
