I just took a look at two guns I own with conventional hinge pins with double underbolts, one a J P Sauer the other a J P Clabrough. Both have the hinge pin supported by the frame. Both have the bbls joined by braizing, the Clabrough with a dovetail lug &Not Chopper) & the Sauer with a shoe lump. Both are over 100 yrs old, both show considerable use or at least handling, both are still tight & on face yet "Neither" have wear compensating "Anything". The bolting surfaces on both the bolt & the lug are simply paralell, no wedge shape.
Both of these guns have the forend secured by a deely latch, no spring loading to give frictional wear to mating surfaces. The benefit of the bearing area of the rear lug is of course highly dependent upon its fit (workmanship).
Again the main point of the 21's fame is its metalurgy, not any superior design. The Model 97, 12 & A5 put more double gun makers out of buisness than the 21 ever thought of.
Just as a side thought, anyone have any idea what type metal & type of bbl joining was used for Jefferey's .600 NE.
