The question about wall thickness just in front of the chamber was important to me, as I have a couple great old guns that have been lengthened from 2 1/2" to 2 3/4" chamber without reproofing. One was done by a very reputable gunsmith operation and they assured me it was safe to use. Both are over .100 right in front of chamber. I was doing research and found in one of Gough Thomas's books where he measured pre war English doubles and post war Italian, Spanish and Japanese guns. The English were from .106 to .122 with several in the .113 range. The post war doubles were .076 to .086. He also discusses elastic limits and a safety factor of 2, states a gun with working pressure of 3 tons should be .084.

This ain't a dress rehearsal , Don't Let the Old Man IN