Interesting find! It sounds like you have a unique single-shot pistol that might have been converted to .22 Hornet caliber.

The magled screws in the backstrap could definitely be evidence of a stock mount that was previously removed. Stocks on single-shot pistols can improve accuracy and stability.

Relining a pistol barrel to .22 Hornet is uncommon, but possible. It would be helpful to have a gunsmith confirm the caliber and assess the quality of the relining work.