Choke measurement tool

Don’t have that one but I have others that are similar, they don’t agree with each other often.

Choke designation is an odd thing. The definition is a certain %of pellets in a certain sized circle at so many yards. It can only be an accurately determined by shooting the shotgun. You can look up the numbers.

Secondary to that it is the amount of restriction at the muzzle from the bore further back. Two barrels can have the same choke with different muzzle sizes if the restriction is the same. You can measure that with a micrometer.

Or you can just measure the diameter of the muzzle opening, the least accurate method.

I have a Remington target barrel that uses screw in chokes. One choke measures modified but when installed measures full due to the over bored barrel. The others in the set say extra full and something else, don’t remember now.

Edit: full, extra full and super full on the target barrel chokes.
 
I have one very similar to that one but I don't know that I believe what it indicates. It indicates every bore is more open that indicated by the manufacturer.
 
Each mfr has its own take on choke. Then you introduce backboring, overboring, lengthened forcing cones, etc. & the whole thing gets complicated even more. But McFarmer is right that the proper way to determine choke by measurement is to determine the amount of constriction relative to the bore. I put this together a few years ago, based mostly on info from Briley. As I recall, though, I used other methods to estimate parts of it. Extrapolation. Averaging what I thought seemed like the "best data". And possibly some other techniques that could arguably be considered somewhat suspect.

choke constriction bhm.JPG
 
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