The Hartzell prop has both counterweights and spring(s) for actuation. Per their service manual:
Operation is such that the counterweights provide only sufficient force to neutralize blade twisting moment. Governor oil pressure rotates the blades into low pitch (high RPM) and reverse blade angles, while springs contained within the hub assembly rotates the blades towards high pitch (low RPM) position.
Thus to feather, just remove oil pressure, and the spring force feathers the prop. And their reputation is that feathering is pretty quick!