I recently watched a YouTube video by “tinkertalksguns”. He related how he converted a single shot top break, hammer fired shotgun to 22 Hornet. He had video footage (and a nice red divot on his forehead) showing him firing the rifle and the firing pin blow out and wack him. He postulates the firing pin was held in the breech by a small set screw. The higher pressure of the Hornet cartridge was too much for the set screw to hold. Seeing the video footage, I have no reason to doubt him.
Here’s a link to the video:
https://www.youtube.com/watch?v=v8lC7WEFK3U