At a club shoot yesterday we had an incident that could have been really tragic for one of our shooters. He was shooting a percussion .50 caliber Lyman Great Plains Rifle with GOEX 3fg powder. He'd been shooting for a couple of hours and he doesn't clean between shots until it gets hard to load. This is, as you know, a practice many shooters follow all the time. He returned from the firing line to the loading bench about 20 feet behind the firing line, put the rifle on half cock, removed the old cap and began to reload. He poured the powder from his can into his powder measure, covered the powder can spout as required in our club, and poured the powder down the barrel. He took a lubed patch, placed a ball on it, and using his short starter, started it down the bore. He then took his range rod and had just started to push the ball down the bore when all $#*! broke loose.
The rifle fired with a loud muffled sound sending the range rod and ball through the 3/4 inch plywood and shingle roof about 10 feet over his head and up through the branches of a tall pine. The badly twisted metal rod was recovered about 25 yards out on the range. When the range rod he was holding came flying out of the barrel it severely lacerated two of his fingers and broke one of them. Apparently that knocked his hand out of line with the bore and the ball didn't hit him. However, it certainly called for a fast trip to the emergency room after we got all the bleeding stopped.
Our best guess as to what caused the ignition was a smoldering ember back in the patent breech or even in the flash channel that was far enough back that the powder poured in the barrel didn't initially contact it. However, when he started the patched ball down the bore the resulting air being compressed ahead of the ball pushed the powder onto the ember.
I think there is a very good chance that had he wiped the bore with a wet patch between shots this might not have happened because (1) he might have contacted the ember with the wet patch and put it out (2) the compressed air ahead of the wet patch might have caused the ember to flare up and burn out (3) the extra time required to wipe the bore with a wet patch might have allowed the ember to die out on its own.
I always wipe the bore between shots with a wet patch because it seems to improve accuracy for me. But the added safety aspect is something to think about.
Mole Eyes