Thanks is correct, measuring is fine, but patterning is the best.

I have seen on some sites, guys that buy guns sight unseen and have chokes listed that they don't like, the first thing they ask is whom to send the gun to ream out the chokes. I used to respond, get the gun and shoot it first and then decide what you want. I don't do that anymore because those that ask don't know that once metal is removed that's it.