Briley and Seminole will make tubes to your specificatons. If your bore is .734 and your desire a constriction of .003 then Briley will make a tube measuring .737. They have never charged me any extra for this.
The Briley "Series" are based on the external diameter of the tubes and of course your bore size. I have a Winchester M21 and a Merkel 47E that use S-1 series. The tubes interchange between the guns. I also owns guns that use S-2 and S-26. If only they were all the same bore size...
Seminole states that they need your bore size to make the chokes.
