Keith, another thing to note is double underbolt guns being fitted on the circle (or lack thereof). I recently discovered that almost no shotguns were actually fitted to make contact on the draw, which undoubtably contributes to their going off face faster than they should - they're bearing the entire fore-aft forces from recoil just on the hinge pin. This is the case even with the British Best guns, much to my dismay.
There are very, very few manufacturers who properly fit their shotguns on the circle. Some Merkel guns have a little removeable insert of hardened steel in the draw and can be made to bear on the circle reasonable easily. Fratelli Rizzini guns are properly fitted.
Kip,
The Baker Gun & Forging Co., starting with the Hammerless models in 1892 and also the Model 1897 Hammer gun gun(Syracuse and early Batavia), utilized a cross bolt in the barrel lug that engaged a cut in both sides of the frame. This in theory relieves stress on the hinge pin and holds the barrels tight to the breechface. This combined with the bolted barrel extension seems to make for a very strong lock up. Again, only if properly fitted.
John
