Doc, the pictured door looks like it came from a US military rifle of some sort; Krag, 1903 or 1917. The original hinge boss can be attached to the inside of the buttplate by welding or silver-solder, and the spring-loaded closure can be obtained by either an adaptation of the original GI leaf spring or else a coil spring in a blind hole with steel cap to bear against the hinge. The inside butt of the hinge has a right-angle heel to hold it securely in both the closed as well as the open position. Taper the door seat to obtain a flush fit like the original GI one. A really nice touch would be to actually checker the door to match the plate but it would be difficult to say the least.
I've obtained some blank oval door castings (doors only) sized for the old Albright trap butts, checkered but not drilled for the hinge yet. If you'd care to try one of them, I'd be happy to gift you if you'll pay the postage. It's about 2" long by 3/4" wide, approximately the same size as the old Mann-Scho doors but not curved quite as much. The opening is just right for the slide of a Lyman 48....
Regards, Joe
