Quote Originally Posted by Woodsheal View Post
It's most likely hanging barrel down, clipped to a separate strap that doesn't show up in the painting.
I agree. Scottish pistols in that era typically had a belt clip for attachment to a strap or belt, rather than being carried holstered. There are some good example pics from a modern reproduction here:

http://www.middlesexvillagetrading.c...tmurdoch.shtml

A close-up: