i suspect there is a bit of artistic license in the depiction of the weapon in the painting (and of the dog

).
p.s. -i'd posted (as attachment) a large screen capture of the hunter so we'd have it available in case Miqueleter's link broke. i have since found a much larger image of the whole painting to cut the hunter from & attached it above instead.
p.s. - don't think that helped much, still too little detail of the lock.