Chokes not only add a little weight (a few ounces), but the main thing they can do is change moment of inertia by having that weight at the very end of the barrel. Wood density, recoil pad or butt plate also add into the equation. I have found the better balanced guns to have fixed chokes with slender barrels. Choke tubes necessitate a thicker barrel so it can be reamed at the end and threaded. Some do it by flaring the barrel ends -(IMO it gives them an unsightly bulge as you look down them), others by using a slightly thicker steel. It doesn't take much to make a 6.5# gun weight 7# in that scenario.