Step 1: Storywise the situation can go any way as long as the character doesn't totally die.

Step 2: The PC is way more badass than his opponent, but not superior enough. When fighting with guns superority in skill doesn't matter that much.

Step 3: The player gives a nice description of his character leaping from behind the car with a double flip and throwing a few rounds towards the head of the baddie while flying through the air. The GM, though, has some standards of quality and a good description only saves the player from penalties, way more is needed to gain bonuses.

Step 4: Yeah! Our PC is Very Dangerous and Fairly skilled. His BT+GT is thus 9(5+4). He's going for the head while flying through the air, so his chances are Poor(-3) (in a different genre they might be Terrible or worse, now the flying is almost mandatory and the penalties come only from the selected hit location). The baddie was standing still trying to listen where the PC was hiding, if the baddie had been on the move, the shot would've been more difficult. Remember that the chances aren't affected by the skills of the character, chances represent a genre-based basic chance. The character's own abilities are his BT+GT. The total before the roll is thus 6 (9-3). The player rolls 2d6 and gets 5. A close call but he manages to get a hit (6-5=1). Since the shot was aimed for the head, -1 could have still hit other parts of the NPC. The positive result tells that the attack hit exactly where it was aimed. The PC shot "a few rounds", so a greater success could have meant many hits. The GM determines that with the +1 total, one bullet hit the target in the desired location, and all other bullets went to the sky.

Now for the damage. The NPC has BT+GT of 3 (BT used is "moderately tough", the baddie has no GT to help him survive bullets to the head). The GM determines that a bullet to the head is very difficult to survive, so he makes the dangerousness -7 (definitely bad, multiple hit would have granted -9 or worse). The margin of success was +1, so that gives a -1 modifier to the damage. Total damage is a whopping -5. From a good status (6) the baddie no drops to an incapacitated status (6-5=1). That's what happens when shot to the head.

Let's take an alternate route. What if the player had rolled 8 in stead of five? His attack would have totalled (6-8) -2. Because of the head aim and multiple bullets, GM decides one bullet still hits torso, despite the "miss". Now let's calculate a different damage. The baddie wears kevlar, so the chances of him surviving are fair(+3). The total damage is 8 (3+3-(-2)). That's +8, so it's ignored, +8 is enough for the NPC to not even notice the hit.

So can kevlar be overcome with 9mm bullets? Our character now shoots the same baddie with a straight aim. Chances to hit are quite good(+4) and he rolls only 3. His margin of success is 10 (9+4-3). The baddie had BT of 3 with fair chances(+3) of surviving thaks to his vest. He still gets 4 levels of damage (3+3-10). This time the vest fails the baddie. On the other hand, our PC is quite a wizard, an average shooter might have BT+GT of 5, instead of our examlpe's 9. An average gunslinger like that would've not had a similar knack at trying to shoot through a kevlar vest. In fact, he could not have made any of the shots in this example.