Hi James,
The style of the butt stock may be about right for the late 17th century but I believe it has been reworked into a half stock during the late 18th century at the earliest. How many 17th century British guns have you seen that have barrel ribs, barrel keys, and horn nose caps? Also James, notice that the barrel key heads are on the wrong side for a British gun. This gun has been horribly diddled with.
dave