To the best of my recollection I have three doubles on which the top lever was made to center & remains centered after more than 100 years each. One is American (Lefever), one English (J P Clabrough) & one German (J P Sauer & Son). Of these three only the Lefever has bolt wear compensation. The lefever is a side pivot opener with a vertical bolt entering the rib extension from the rear. Compensation is applied via a screw through the top tang over the bolt.
Both the Clabrough & Sauer have double underbolts with a Doll's Head. The notches in the underlugs are simply cut on a horizontal plane with the bolts fitting with minimum clearance to allow bolting. Both show considerable use yet both remain tight with no slop in the bolting. Sort of makes one wonder if the "Tapered" bolts to provide wear compensation doesn't actually induce as much wear as they compensate for. None of these guns have a latch for the lever, it being cammed over in closing. As the bolt comes in line with the notch it snaps home. "IF" the bbls are closed smoothly yet firmly, the bolt actually snaps home virtually without touching the notch surface to produce friction. A wear compensating bolt always seats with friction on the taper.
The Lefever also bolts tight, but of course I cannot say if it has ever been adjusted or not.
