Jörg, my idea also has a lever pivoting from the bottom, but all the motive force comes through the lever. There is a powerful band within the handle trying to pull the lever out, and the lever pulls on two lines of cord going up to two eyes on the ends of a fork. The advantage is leverage delivered in essentially a trigonometric TAN function, i.e. having considerable let off at full draw and full torque and max velocity as the pouch reaches the fork. You may want to try this; you have better skills than I in the fabrication of moving parts.