Fletched Pair,
Sorry for the tardy reply.
I was informed by a learned gunmaking friend and colleague that the shape of the triggerguard originates from the fore hand hold used by northern continentals in target rifle shooting.
The triggerguard is balanced on the extended thumb with the first finger on the forend just in front of the knuckle.
Apparently the logic in target shooting is that when shooting a rifle standing without support, it stopped one gripping the barrel and pulling the shot.
The practice carried over to shotgun shooting and survived up to the 1st WW but has since died out.
And no, I wasn't having my leg pulled!
The horse scabbard theory sound plausible except that I don't imagine that wealthy Austrian aristocrats rode out to shoot driven pheasants but if they did, their guns were most likely consigned to a very elegant horse drawn carriage that preceded them to their battue.
