The helicopter pilot reported that, during startup on an off-airport landing pad, the helicopter was facing into the wind and the airspeed indicator was shoring gusting wind conditions. As the blades began to turn, he felt a strong gust of wind and heard a loud bang almost simultaneously, and the helicopter "lurched" to the right about 5 degrees. He immediately aborted the start procedure and applied the rotor brake. A postaccident examination revealed the helicopter's main rotor blade had struck the tail rotor driveshaft cover and damaged the tail rotor drive shaft and support assembly. The pilot reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation. The pilot reported the weather at the accident site, about the time of the accident was, wind from 130° at 25 knots, gusting to 30 knots with light terrain-induced turbulence. The flight manual states that the wind envelope for spinning and stopping the rotors has been substantiated for winds of 40 knots from any direction and for 50 knots headwinds.