Displacement-controlled (DC) actuation is a revolutionary fluid power technology which has been utilized on a broad range of applications demonstrating substantial fuel savings and significant performance improvements over traditional valve-controlled (VC) systems. In this paper, a nonlinear discontinuous projection-based adaptive controller is synthesized to achieve precision motion control of DC actuators. The controller is formulated to compensate for uncertain parameters through online parameter adaptation. Additionally, its structure allows for the inclusion of unmodeled nonlinearities such as friction and external loads and disturbances. Transient performance and tracking accuracy are also guaranteed in the presence of both parametric uncertainties and uncertain nonlinearities, and asymptotic tracking is achieved in the presence of parametric uncertainties. To evaluate the synthesized controller, a test bench comprising a large hydraulically powered end-effector was utilized. The actuator, a vane-type hydraulic motor is mechanically connected to a large robotic arm with a wide range of motion. Measurement results demonstrate that the synthesized controller achieves the aforementioned advantages while attaining a high degree of motion accuracy.