All the flint muzzle loaders that I can recall have front action locks, because part of the mechanism is mounted on the lock plate below and forward of the touch hole. I have never seen a flint lock with a back action lock. For some reason I have always associated muzzle loading double shotguns with front action locks with the higher priced/higher quality guns.
Tom, you make an interesting point. I had a 36 gauge Belgium made ML that I always thought was an early youth gun. It had a 13.5” LOP but what I found interesting was the lack of quality in the engraving and checkering. It was as if it’d been engraved and checkered to be “Just like dad’s gun!” It also had back action locks. I must be a kid at heart because I really liked the little SXS and used it to hunt preserve pheasants. When I was hit by a tsunami of health and financial problems around 2009 I was fortunate enough to be able to sell it to a board member who I knew would take good care of it.
Steve