Your capbox appears to be pewter, as you thought, same material used for cast nose caps on many later half-stocked rifles. Your capbox may have been cast in place, similar to casting a nose cap in place, and then screws added to make sure it didn't loosen or pull up over time... since cast pewter isn't as rigid or strong as cast brass... and maybe that's why the lid failed. The lower edge of the finial seems, in my view, to have a slightly feathered edge, which can occur if cast in place. The slight irregularities around the capbox's perimeter suggests it was hand-made by the gunsmith, one of a kind. If cast in place, the mortise may have been undercut around the edges to better hold the box in, so....... be careful if/when you try to remove it.
One possibility for an almost-matching lid would be to use the closest standard brass lid, and when fitted and installed, rough the lid's outer surface and simply coat it with a soft, non-silver, cheap solder and wipe off the excess. It should stick to the clean/roughened brass, and, with a little time, it will turn gray. If not gray enough or the color you want, get an even cheaper solder and simply do it again.
I would be uncomfortable trying to shoot this rifle again with its re-glued stock, since you know nothing about how it was "fixed." Whenever a major wrist break occurs, the stock's integrity is compromised. If the wrist repair is an old glue joint, it probably used only glue, without any dowel rods or pins to hold and reinforce the joint and better insure the two parts stay together... and can tolerate hard thumps again. Sometimes these old rifles, when heavily used and damaged, are best just restored to look whole again, and then put back up on the wall to enjoy and think about what they may have seen during their working days.
Shelby Gallien
