The Good Book reads...after the shooter indicates to the RO that he is ready, the RO goes to Stand By and off we go.
However, if you are at a friendly match, as I was, I was an RO who reminded the shooter to put a mag in his gun after he said that he was ready. He just had one round in the chamber. I did not go to Stand By. Once the buzzer goes.......it's showtime. Mandatory reload on the draw? Do it. Go, go, go or take a DNF.