I know one in a chamber is where one bullet remains in the gun. The common method is where you reload half empty magazine and the bullet get stuck there due to one round automatically rise up after shooting one round.

I know pistol tend to do that but what about assault rifles, they act similar to pistol in semi automatic action. Would that explain why there is no full reload in video games when you reload the rifle half way and only a full reload if the rifle is empty.