I'm looking for a movie that was showing in the early 1970's in the US at the drive-in theater, so I assume it was of that era. I will also assume it was a Hong Kong film.
In the film, a master is training a student. part of the training includes the student driving his fingers into a barrel. I think early on it was filled with sand, but he worked his way up to a barrel of rocks. of course, it was agony for him at first, but eventually he could do it.
I don't remember anything more; sorry, I was just a kid falling asleep in the back of the car, but that scene stuck with me.
I remembered a small detail: at the end of the film, during a big fight the hero was able to jam his fingers through the chests of his enemies.
I believe the barrel training sequence was in a dry, perhaps desert location. I recall the hero trained by alternating his hands in the rocks, not by pushing them in at the same time.