The pilot of the tailwheel-equipped airplane reported that he landed on the main wheels, and while waiting for the tailwheel to drop, the "tailwheel jammed." He added that, when the tailwheel touched down, the airplane was difficult to control and veered to the left. He corrected for the veer, but the airplane veered to the right. He then conducted a go-around; however, once airborne, the airplane "did not appear to be producing proper power." He then aborted the go-around and opted to land on the remaining runway. About 25 ft above the runway, he set the airplane up for a wheel landing and descended. When the airplane was about 5 to 10 ft above the runway, the airplane "abruptly" sank and landed hard, and the main landing gear collapsed. Subsequently, the airplane came to rest nose down on the runway. The airplane sustained substantial damage to the fuselage. During a telephone interview, the pilot reported that he believed the tailwheel had jammed before touchdown and that he had previously redesigned and altered the tailwheel. Further, the airplane produced insufficient power during the go-around. He reported that the tailwheel was mechanically "okay" when examined after the accident. Additionally, an airframe and powerplants mechanic reported that he examined the tailwheel assembly after the accident and found no defects and no binding. The pilot reported that the weather at the accident airport, about the time of the accident, was wind from 320° at 10 knots, gusting to 12 knots. The pilot landed on runway 31. Photographs taken at the accident site showed torsional twisting of the propeller, consistent with the engine producing power at the time of impact. The National Transportation Safety Board did not examine the engine.