Thought I'd post what finally happened with the BSA.
Seemed like a pretty standard box lock, so off came the stck and the floor plate. Nothing obviously broken. Took out the sear springs, punched over the pin holding the sears, & removed the sears.
Turns out there was a little disk of metal holding the right sear out so it wouldn't catch the hammer. A pierced primer must have blown the disk back into the action, where it rattled around until it landed between the hammer & sear. For good measure, I blew out the action with carb cleaner and tri-flow, reassembled the gun, & it's good as new.
Regards,
Ron
