Miller you and Chuck are both certainly advocating that the twisting of the gun is enough that it rotates the axis of the barrel from its initial convergence point to the POI axis in the short time it takes the shot to move from the breech to the muzzle. Using Chuck's 1-1/2" and subracting my 0.8" and dividing by two it is about .35" of displacement in the few thousandths of a second it takes the shot to go from breech to muzzle. And the rate of rotation is much higher at the time of shot exit than at the beginning (0).
My theory is the more likely because the rotation of the barrels in those few milliseconds would be less than the .35" you and Chuck are arguing for.
Of course it wouldn't take a very large side vector to make up a convergence (rate?) of .011".
