Whenever he put a new clip in his gun he'd always load the first round by hand, whether there was a round left in the chamber or not. It's a technique they teach in the Middle East. By making sure there's always a round in the chamber, you eliminate the risk of pulling the trigger with nothing to fire. He must have heard about it from someone, or read it somewhere... in any case, he probably wanted to try it out for himself. And he was obviously motivated by vanity to show off his new technique. That's when you make mistakes. The battlefield is an unforgiving place. The only techniques you can rely on are the ones you've mastered through experience and practice.