Any ideas or information on this MYSTERY Percussion Pistol?

Years ago I was told that this percussion pistol was made out of an old rifle in the 50s. I didn't really wonder about it until I noticed a couple of things about it that got me wondering if that was the straight story. I assumed they meant it was made from a modern rifle, but the compartment that the nipple screws into looks like it has always been there. The sights show no sign of being altered. The nipple looks very small for a rifle percussion cap. The bore of the thing seems to be around .30 cal. Isn't that just too small for a percussion rifle? Another thing I don't understand is there appears to be two quarter inch holes filled in on the butt of the pistol with dowels. That is very well done but I can still make them out. There is a hole for the ramrod but it is missing. So I guess my question is: Was this converted from a modern rifle, a percussion small bore rifle or has it always been a pistol? What year would you assign to this?

Pictures:

https://www.facebook.com/media/set/?set=a.31311236...