I would not shoot the gun until I repaired the nipple seat and installed a new nipple.
Larger hole at the top, tiny hole at the bottom.
The gun test you refer to was Colin Stoltz and Son on the 2-bore double he built.
Cap lock rifles that have a drum sticking out the side of the breech, sometimes spit the drum out the side when the threads become loose from over use.
I would not trust 2 1/2 threads