On August 21, 2019, about 1235 eastern daylight time, a Cessna 310L, N2299F, was substantially damaged when it was involved in an accident near Tampa, Florida. The commercial pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that, while on landing approach, the right main landing gear would not indicate down and locked. He "wiggled" the light for the right main landing gear and changed the light bulb, but the right main landing gear did not indicate down and locked. He continued the approach and landed, but during the landing roll, the right main landing gear began to collapse. He aborted the landing and climbed to altitude, where he cycled the landing gear and tried to extend the right main landing gear using the emergency gear extension procedure multiple times. He also attempted abrupt maneuvers but was unable to get the right main landing gear down and locked. He then attempted a second landing, with the same results. After the aborted second landing, he contacted air traffic control, declared an emergency, and diverted to a tower-controlled airport. He performed one low pass and one fly-by of the air traffic control tower and was told that the right main landing gear appeared to be down. He returned for landing and, during landing, again felt the right main landing gear was collapsing. He aborted the landing then informed the tower controller that he would land gear-up. He subsequently performed a gear-up landing. The pilot/operator subsequently reported that the damage to the aircraft was substantial. During recovery of the airplane, airport maintenance personnel were unable to lock the right main landing gear using the emergency gear extension system but were able to manually push the gear over-center and brace it. They also secured the nose and left main landing gear over-center with heavy tie wraps and towed the airplane to the ramp. The airplane was examined by a Federal Aviation Administration (FAA) airworthiness inspector following recovery. The inspector reported that he could not determine the reason the right main landing gear would not go into the down and locked position; however, no disassembly was performed to gain access to all components of the right main landing gear retraction and extension system.