nigelh,
The blades produce a downward pitching moment as they get near stall, so they must be producing a high percentage of their maximum lift to produce jack stall. In other words, jack stall is NOT a hydraulic situation, it is when the blades produce enough control force to stall the hydraulics because the hydraulics are too small. This stall force is caused by the same airfoil pitching moment that makes an airplane dip nose down at stall. Remember that stall can occur at low maneuver rates, if the DA is high or the MGW is high, so don't think cowboying is how you get jack stall.