My brass pan charger occasionally leaks a dribble, so I clean it out. I also keep it covered or in the bag when firing.
That brass tube is nice & heavy, machined out of bar stock.
Should the priming ignite in it, there will be some worthwhile pieces of brass flying about & perhaps through one's hide.
So my next project is to make one of antler. If it blows less damage should be done.
There is a reason, by the way, that old flasks are made in two pieces joined by a very weak soldered butt joint. Lousey joint design for strength. One does not want one's powder container to be strong. Powder is supposed to explode. Sometimes it does so when one might prefer it not. In that unlikely, but really happens, event a weak powder container permits one to retain most of one's (burned) flesh.
Don't know anything about what knapping does to a brass priming tube, but I respectfully suggest you reconsider hanging it about your neck.