User blog comment:Abranon/Why didn't Regulus Black do more to contribute to Voldemort's Death?/@comment-117.254.147.208-20120125142953

Regulus probably did not know all of the protections in and around the cave. He might have just gone there to get the locket. Once getting the locket, he would have tried to destroy it. Only after seeing the actual protections, he ordered Kreacher to save himself (Kreacher) and destroy the locket.