Some early Syracuse Lefevers are bolted by the so-called Pivot Lever system, in which a spring loaded bolt is retracted to open the gun, and the lever then returns to center under spring tension, and the bolt extends. The bolt is cammed back by the rib extension upon closing. This is pretty similar to the even earlier Thumb Push opening system. Dan Lever incorporated a method to tighten up bolting as it wore and the gun became loose. However, I've seen very few in need of tightening, even though all of these guns are over 125 years old.
Somewhere around serial number 15,000, Lefever used the more conventional top lever which was held open until the trip mechanism permitted it to return. The system used a single bolting point on the top rib extension, and the bolt had a very slight taper which allowed the bolt and lever to gradually move toward center, or even left, as the bolt and bolting surfaces gradually wore. Apparently Dan Lefever felt this was an improvement over the earlier system that wasn't self-compensating for wear. He was able to eliminate the adjustments for wear, but had to add the lever trip mechanism.
His last guns employed a cross bolt, which of course required a top lever that is held open until the trip is activated. The cross bolt had a very slight taper, and there is an adjustment screw to permit the cross bolt to travel slightly further as wear occurred.
It seems to be a combination of the design, engineering, cost, difficulty of machining, and the fit and quality of the materials that determines which makes of guns wore out prematurely, and which stood the test of time.
