This thread's got me looking. In my three doubles, two British, one Italian, the front lump recess is parrallel, but the rear fits in a reciprocating wedge form with the underbolt.
Don Moody, thank you for the info on the bushing. It is a nifty idea for sure.
Piper, the idea od inbuilt wear compensation makes sense. I have seen hundreds of "best guns" off face and seen many strange ways of repair. Some forethought that would prevent TIG welding the lump is not a bad idea in my view. The replaceable bushing is a simple way to offer built in renovation and to stop any "innovative" smith from doing weird things. Beretta and Blaser, to name two, use these devices in their OUs.
As to the metallurgy versus design concept. It would seem that the material specified is part of the total equation, as is the manufacturing method. Bruce Owen, production manager at Purdeys, wrote a long time ago in Shooting Sportsman that Purdey had to change to modern steels when it went over to CNC machining. The old stuff just could not handle the faster feed and cut rates of the new machinery. If I recall he used the words "better steels" which kind of raises interesting questions as to the term "best", but that is for another thread.
