Are there photos attached somewhere that I'm missing? There are British steel loads which are specifically made for guns that have not passed steel shot reproof. However those shells have very different ballistics (lower velocity, lower pressure, smaller shot sizes) than those approved for guns that have passed steel shot proof.
I imagine it doesn’t take more than a box or two of those lower velocity steel loads to convince the owner of an old double that he has to up his game with a newer gun that can handle the hotter loads. Then another old double hits a saturated market.
Many of the boxlocks that had the overhanging sears have had them disabled at this point in time. Adding them after the fact would seem a fools errand, drilling and tapping a case hardened action to install a system that history deemed less important on a boxlock than the system used on a sidelock. The angle of the sear in the bent does a pretty good job of preventing a boxlock from firing unless the trigger is pulled.
This isn’t the case on a typical sidelock gun.
The screws in the action flats I haven’t a clue. They were timed nicely when they were put in. That probably cancels the notion that they adjust anything.
Best,
Ted
