Yeah, many "improved cylinder" chokes will pattern 60% or more with hard shot, especially larger shot.
A lot depends on the exact constriction. I've measured supposed IC chokes on 16's that ran anywhere from .008 to .014, and have seen modified chokes measuring .010 to .020.
Nail on the head Sir. Large, hard shot.
No doubt the manufacturers of chokes have their standards of constriction for chokes, but they don't watch it too closely.
