Great find! You did well I think.
It appears to be a fine Murdoch style Scottish pistol, though I have only seen those as flintlocks. This one was not a flintlock unless the lock was changed (there are no indications of the lock plate being a flintlock), and the percussion nipple bolster looks integrated to the barrel breach, so unless it was re-breeches that barrel was always a percussion. So time period of 1830’s or later.
From the absence of engraving on the off side ( opposit the lock) it looks like it may have had a belt hook, a common characteristic of the Murdoch pistols.
One suggestion would be to replace the Philips Head screw (not original and not period) with a slotted screw.
PS- check that it is not loaded.