As a follow-up to my first post, many shotgunners (especially hunters) apparently think chokes marked with a certain designation are all exactly the same constriction--and they are not.
I've owned a shotgun barrel measuring gauge for over 20 years, which allows me to measure not only chokes but interior barrel diameters. In 12-gauge alone (which might be expected to be the most consistent) I've measured bores varying from .720 to .743 inch in diameter, when the supposed industry standard is around .730.
Have also measured the inside diameter of 12-gauge chokes, whether screw-in or fixed, marked in various designations:
Improved cylinder: .715 to .720
Modified: .702 to .707
Full: .682 to .697
Throw all those variations together and it's obvious that the actual amout of choke contriction, compared to the bore, can vary enormously. Which is exactly why we don't really know the amount of constriction just by measuring the interior diameter of the muzzle.
