In this instance, the ‘Bullet’ ward is the horizontal groove machined into the Blade / Flag of the key .The keyway will be shaped so that a small protrusion will fit into the groove as the key enters the lock. The keyway on the other side of the lock is similarly shaped. If both keyways are viewed from one side of the lock, then the far side keyway will appear mirror imaged. Because of this the key cannot pass through the far side of the lock.
If you number the steps (bitting) of the key, 1 to 7, left to right. When the key has entered the lock, (let us say the outside of a door.) Depending on which way the door is mounted , then steps 1, 2,3,4,5, operate the levers. Step 6 does nothing and step 7 operates the bolt. If the key is used from the inside, then steps 7, 6,5,4,3, operate the levers. 2 does nothing and 1 operates the bolt.