According to the pilot/owner/builder of the experimental amateur-built Prostar B, he was completing his first traffic pattern of the day, which was also the airplane's fourth flight. While on final approach for landing on Runway 23, the airplane's alignment was "a little left of centerline." The pilot said that as he adjusted the airplane's alignment with the runway, his airspeed "bled off" before the airplane "ballooned" and then dropped to the runway. The airplane experienced a hard landing, the main landing gear separated, and the airplane skidded to a stop on the runway. When asked about the performance and handling characteristics of the airplane, the pilot reported that the airplane was running fine, but that the left wing was "heavy" and that he had recently made rigging adjustments to correct it. Examination of the airplane by a Federal Aviation Administration inspector did not reveal any preimpact malfunctions. Winds reported at the airport were from 140 degrees at 5 knots.