I am trying to repair a BSA .303 cal rifle for an old friend. The trap door in the butt plate is slightly bent and it stands above the plate when closed. I thought I could remove it to flatten it flush with the plate, but I have no idea how. The hinge pin is hidden and I don't know how to remove it. There is no visible hole. Are these similar to the spring-loaded pins for wristwatch bands? Is the hole tack welded shut or peened over? I would appreciate any info on this. Thanks.