Matt,
You have the right idea about lock removal. The flint cock, frizzen (steel), and lock plate should come out as a unit, complete with the lock innards. If the cock seems to be spring-loaded, you have a mainspring intact, and the cock could possibly spring forward suddenly and with force, when you work the lock out of the rifle. If the lock doesn’t want to come out, screw the lock bolt back in about two revolutions and tap the head gently until the lock moves sideways.
Another thought about the hole in the butt: If it seems to run parallel with the barrel, it may have been the receptacle for a base-mounted stiff rod to hold the lamp upright. The cord would then have had to pass down the outside of the gun, in which case you will not find a cord channel through the breech plug and stock wrist. If the hole points toward the center of the wrist, than I would expect you will find a cord channel. An oil lamp could have been mounted on the pipe thread, doing away with the cord, but that would be a new one in my experience. Hopefully the barrel hasn’t been drilled and the lock altered.
Was this an old family gun, or a later pick-up before you inherited it?
If the breech hasn’t been drilled out, I would consider getting the lock to work and not doing much else to preserve the gun. The lamp story is part of the gun’s history by now.
Bill Paton
PS: After my slow typing, I see Ron has caught his thumb between a flint cock and lock plate, too
