Tom Kilgore posted an interesting question about shooting the new non-toxic loads in a full choke gun. I made up different size 12 ga. bore gages from .732-.724 and measured 10 different 12 ga. Basically all were different in size. Most all have a larger diameter taper right beyond the forcing cone and most/all I could put in a .730 to a depth of 3 3/4"-6", after that they would be different in the right and in the left barrel. A few were consistant in .728 bore size to where the choke started. One a 1919 Field Grade Regular frame 30" barrels was interesting. Initially the chokes miked out at .007 and .013. A .727 bore gage only went in 12 7/8" in right barrel and stopped. Left barrel went in 6". A .726 went in 26 1/2" in right barrel and stopped. Left barrel 11 1/2". A .724 went in 27 1/2' in right barrel, and left barrel 11 3/4". That is the smallest I made, so I will make a .722. I have never patterned this gun and would really be interested in what it does.
The whole gist of this is, does it really prove anything by just miking the ends of the choke area. Does the area leading up to the choke have anything that leads to better patterns. I would say yes, and in my opinion just what the readings are at the end of the barrel mean nothing really, patterning it will tell what it actually will do. You might have to use a half dozen different types of loads to get that "right" pattern. and they say the only real way is to bench rest it every time. A lot of work and time.