According to the pilot, the purpose of the company test flight was to measure collective stick forces with the collective bias disabled. The pilot, who was the helicopter's only occupant, lifted the helicopter into a hover and then hovered clear of any obstacles. He reported the collective controls were heavy as expected, but the helicopter was very controllable. During his attempt to position a force gauge between his hand and the collective grip, the pilot lost control of the helicopter and it landed hard onto the ramp. The helicopter's tail rotor blades impacted the ramp and the helicopter came to rest upright. A postaccident examination of the helicopter showed the tail rotor blades were bent, and the tail rotor drive shaft was sheared. The pilot reported he should have taken an observer or other personnel on the flight to assist while he concentrated on flying the helicopter.