LOL, good post Rhino. I had the same thing happen to me last match. Rehearsed it endlessly, and screwed up after the beep. I think it has to do with the way we rehearse. You can SAY: popper, popper, paper etc. etc. But it's probably better to SEE: Popper, popper, paper etc.
Just make a little movie in your head of how it will look after the beep. Make the movie positive. See your sights appear on the targets and see them lift off the target. Stuff like that is much stronger than just repeating words.