On November 14, 2015, about 0950 central standard time, a Robinson R22 Beta helicopter, N7058Z, experienced a hard landing following an autorotation near Sugarland, Texas. The private rated pilot sustained minor injuries and the helicopter was substantially damaged. The helicopter was registered to Jerry Trimble Helicopters and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan.According to the pilot, after flying for about 50 minutes the main rotor rpm over-sped, and went to the top of the gauge. The pilot reduced throttle but was unable to get the rotor rpms within limits, so he initiated an autorotation. The pilot maneuvered the helicopter to an open field location and landed hard. After the initial impact, the helicopter rolled on to its left side. The tail boom was severed from the fuselage during the impact, and was displaced about 150 feet from the fuselage. The pilot reported that the helicopter's rotor had over sped about 2 weeks prior to the accident. A 50-hour inspection of the helicopter did not reveal a reason for the main rotor over speed. The pilot suspected a mechanical malfunction resulting in an over speed of the rotor system. A visual examination of the helicopter by inspectors from the Federal Aviation Administration did not reveal any anomalies.