Against the latest or the previous versions? If this is the full adamantium body ultron, billy would have a very slim chance to get anything done. He doesn't share Superman's ability for heat vision or anything that can remotely able to attack Ultron's innards(best bet is to destroy that molecular re-arranger which allows him to move his solid adamantium body) so he really doesn't have anything to hurt him. Billy might fare a lot better or get a decisive majority from previous versions though.