As an afterthought;
It is a possibility this gentleman in the treestand totally lowered the hammer, rather than placing it on half cock. NO hammer gun should have the hammer lowered on the cap or primer. It only takes a surprisingly light blow to ignite a primer in this situation, much less than enough to break the sear or notch.
This could very easily have occurred in lowering the gun should the hammer have struck a limb or such. Again this not a fault of the gun having a hammer but what we called in the machine shop I worked in OT or OP, ie Operator Trouble or Operator Problem.
I once read an article by a gentleman who was otherwise extremely knowledgeable on muzzleloaders. He recommended when carrying a caplock rifle hunting to lower the hammer all the way down on the cap. His reason was that a blow to the hammer should the gun be dropped or something could break the half-cock mechanism & fire the gun, "WRONG", the blow required to break the half-cock is much more than required to fire the cap with the hammer resting on it.
