Lancaster smooth oval bore rifling, in their Colindian, is same as in all their rifles; it starts where "normal" rifling normally starts, forward of chambers, thus is nothing like Paradox that has the rifling only 2 inches at muzzles. RS wrote article covering his Colindian in Vol. 20, Issue 4, Winter, 2009. Yes, I overlooked mentioning that the oval bore rifling tapers by .002", in both my and RS gun, toward muzzle, but I wouldn't call that a choke, yet maybe you would. It is intended for sealing better conical bullet along the bore, toward the muzzle, with little effect on bird shot.