Loose powder that builds up from repetitive shooting. I saw the granules. Blew them away I thought.
That's what I was told by that gunsmith.
I thought I had cracked the breach, cracked the barrel, really didnt understand what happened. I do now.

ok well that explains what might have happened then,. figured I'd ask as never hearts to learn something new, and or maybe help someone else from having a like issue happen!

anything wood can be repaired better that new (at least stronger) with 2 part epoxy and rubber bands

I used clear packing tape to keep the forearm together. My new Swiss 1.5F powder came and no hangfires or poppers .
I also was taught about the flame channel and taught how to clean that correctly.
my 1st shot, standing looking at a 50 HD target ( bait stump is at 50) and aiming at the 2nd 'O' in Roof. I was happy. Then after days of hunting in rain, dew, sunny to cloudy conditions I always wondered if it would BANG! SO before I had to leave. Same sign, same distance but just a bit left but centered.
I'll still take that. This sharps is way fun to shoot. And the forearm stayed to gather. Now to fix it.