Deltaboy;
This gun is made on the order of the old "Rutledge" bore. They were .22 size for a part of their bore, about 6" as I recall then stepped up to a larger bore & choked at the muzzle. At one point in time a game of miniature skeet was attempted to be popularized, called "Mo-Skeet-O". As to amount of choke you would simply have to measure the bore behind the choke & take the difference. A few tests for patterning ability would of course tell you the most as to it's effectiveness.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra