The hand spring, believe it or not. It is not a coil spring, but a wound spring in the middle with extention wires out of either end to put forward tension on the hand. It is mounted on a pin in the hammer. Not sure what they call that type of spring.
Looking at a schematic. I see it. Hand tension spring. Imagine that. Now I know what bounced off my hand and the cylinder wouldn't turn later. Thank you.