Hi Cerjak,
Congratulations: this is a very nice, sturdy and obviously historically remarkable English flintlock blunderbuss of ca. 1790; please note the shape of the lock parts and the sliding safety catch left of the cock.
The inscriptions, especially on the impressive muzzle face, suggest that it once was used by a postman of the Royal York Mail. Unfortunately I could not identify the proof marks.
Just imagine you were a late 18th-c. highway man trying to mind your 'business', and all of a sudden had to face this muzzle loaded with eight to ten musket balls - reading the inscription while the dog was cocked!
What bore is it?
Best,
Michael