I have a 16 Fox that I chamber sleeved down to 20. Sleeves are slightly longer than the chamber and forcing cones to get a good wad to bore seal and to make the transition to the larger bore less of a fall off. The gun shoots very well and has been a fine long range dove killer. Patterns are about what you would expect for a Full and Full gun and I see no magic in any back bored barrels. They shoot well but I can still miss if I try a little.
Before anyone laments the loss of a 16 let me assure you that the chambers were pitted beyond hope. I chose to go down to a 20 because I thought that making a 20 chamber sleeve would be easier, it was not really that easy, and I wanted a 30" 20 Fox which I lacked at the time. After several attempts and about a bucket of chamber cast I got the job done. If I had it to do again I would pay someone else to do it.
