Strength wise a lot of course depends upon the individual model. Generally speaking a back action SL, or trigger plate action has the potential of being strongest. A bar action SL is next & box locks weakest. In this aspect I would rate the Lefever as being equal to a bar action SL. The frame bar has essentially the same cross section & the hammer axle is well behind the stress zone. Unfortunately back-action SL's also have the most wood removed so often have weaker stocking, Smith's are notorious for this. Again I would rate the Lefever on a par with a bar action, while box locks have the potential of having the strongest stocks (all don't necessarily live up to it). Again generally speaking most (not all) US doubles are built heavier than British or Continental "Game Guns", thus stronger frames.
The hand-detachable sidelock simply has a turning lever formed as part of the head, so a screwdriver is unnecessary. This does away with buggered screw heads, but if one is not careful can lead to removing locks much more often than necessary. This also can be un-desirable as inletting is worn or even chipped. Personally I like an ordinary screw & a precisely fitted screwdriver & don't take the locks off needlessly.
