Could "between a rock and a hard place", be from the accidental release of the hammer of a flintlock rifle, capturing your thumb or finger?
The frizzen, which covers the priming powder in the pan of the lock, must be case hardened to produce sparks as the flint scrapes. metal particles into the priming powder. The main spring on the lock is very strong, for speed and to produce many sparks. The Flint is clamped in the jaws of the hammer or cock, and is knapped or chipped to a near knife edge, I have shot flintlocks in competition for 20 years and have fired over 10,000 times. I have only caught my thumb in the lock twice, both being memorable occasions, and recall them as being "between a rock and a hard place."