My law school torts professor, in private practice, handled a similar fireams accident case in which the safety was engaged on the gun which the hunter's dog knocked over. He and the manufacturer had the piece disassembled on a pure white cloth, and their experts noticed that a small amount of gunpowder came out of the safety. It turned out that unburned gunpowder could be injected into the safety in firing, and so jam it. The manufacturer settled the claim and changed the design.
Trials of a Philadelphia Lawyer, by Lawrence Eldridge.