I was in the Army and Air Force. Every time we drew weapons, we checked the chamber to ensure it was empty. Every time we went to the range, we had safety briefings. We cleared the chambers again before leaving the firing line and the sergeants in charge would run a rod down the barrels to make sure there wasn't a stuck round. We checked the chambers again before turning in the weapon at the end of the day. This stuff gets drilled into your head. It becomes a matter of habit that's harder to drop than smoking.

Think about it, most of the trainees in basic training are still teenagers and they're being allowed to handle automatic weapons and explosives like grenades and land mines. Without a rigorous safety program, you'd have a lot of accidents. You NEVER have your finger on the trigger when you aren't ready to fire the weapon. You always assume the weapon is loaded until you confirm it isn't, then you check it again.