Thanks to all who have chimed in, this sure has been interesting and thought provoking. Ohio Joe's viewing of Youtube videos prompted me to dig in some more on the internet. As you recall, my original question was to learn the safest way to load a single-shot ML percussion pistol. When I was about 8 years old my dad started drilling into my brain not to trust a gun's safety; it's nothing more than a man-made gizmo that can break. This has stuck with me. Also I doubt that anyone would argue the point that something like a hammer, under spring tension, has the potential (albeit slight) to release and cause a spark. Here are loading procedures that I found on the net. The NMLRA says that after loading PPB "bring hammer to half-cock and cap." (They also require flintlocks to be loaded with frizzen and cock forward). Pedersoli instructions begin by saying "with the hammer on rest position (down)" . . . load PPB. CVA says "fire three caps to dry bore and nipple ... load PPB ... with gun pointed in safe direction and hammer at half-cock, place percussion cap on nipple." I found other sites that instruct the shooter to first pull the hammer to half-cock. Even the BSA rifle shooting merit badge pamphlet (the BSA is usually extremely safety conscious) begins with putting the hammer on half-cock. I can't see any advantage to this, the only exception being to vent the barrel as Fyrstyk mentioned, but when loading a pistol I don't think this would be much of a potential worry. I tried in vain to find any original 19th century loading instructions. I was hoping to learn if half-cock was viewed as a loading position or a safe(er) carry position. If anyone has something like that in their collection, please post it. Thanks again, guys!
I doubt you'll find much, or anything at all, with regards to something that was likely to have been considered an everyday regime when it comes to loading muzzleloaders.
One has to remember, folks "back then" relied on common sense when it came to safety, and were handling guns from the time they were old enough to pick one up, and were taught what it took to survive everyday life by their elders.
No muzzleloaders back then, came with written instructions and there was no internet. They were taught to think for themselves and to know their weapons intimately with regards to "form and function".
Have you ever taken a lock apart, and studied how it works?
If so,.... you'll notice that the "safety notch" (half-cock notch) on a modern lock's tumbler has a "lip" on it that the sear's nose sits above to prevent the sear from slipping down from it's intended ("safe") position when at half-cock.
You can check this out for yourself, by bringing your lock's hammer back to half-cock and pulling on the trigger,.... nothing should/will happen, unless someone has messed with that "lip" and didn't know what they were doing.
The only way to over-ride a half-cock notch's "lip" is to bring the hammer back a bit with your thumb while applying pressure to the trigger. That will then allow the hammer to move forward, another way is to bring the hammer back to "full-cock" and pulling the trigger.
Your lock will also likely have a "fly",... which prevents the sear's nose from slipping back into the "half-cock" notch as the hammer moves forward from the "full-cock" position.
I'm not saying every lock is exactly like described above though,... 'cause some
cheap imports from the 1960's and 70's, didn't see the need for a "fly", and some didn't even have a "half-cock" notch.
But to be fair,... I've also seen some antique weapons lacking one, or both, also.
By studying your gun's lock carefully, and thoroughly understanding how it functions,.... you'll be following a 300-400 year old tradition.