For firearms, you can choose to fire multiple shots. Instead of firing one shot, you can choose to fire a burst of three. However what happens, is that you take an accuracy penalty for the first shot, and a acc/dmg penalty for every consecutive shot that is fired, a penalty of 2 for accuracy, and 3 for damage.
Example.
Let's say a guy has a Defense value of 10.
You choose to fire three shots. You roll a D20, and the first roll is for accuracy. In order to land the shot, your roll needs to be 10 or higher. You roll a 12, so the first shot lands. For the second shot fired, your accuracy drops 10, meaning it still hits. For the third shot fired however it drops down further to 8, meaning the third shot doesn't hit.
Then you'd do your damage roll (a D20 roll) to determine how much damage. You know that you scored two shots. So let's say you roll a 15 for damage. The first shot would score 15 damage, however the damage penalty for the consecutive shot.
(Also keep in mind that your marksman trait adds +2 to damage with firearms, for all shots).
Does that make sense?
The benefit of doing a single shot however, is that if you roll high, let's say a 16 or higher, I'll call out special damage states, like "bleeding" or stunned where they take damage or lose defense value for a certain amount of terms. So I guess you can consider single shots to be "called shots", and three shots to be just firing wildly.
If you decide to do something unique that isn't just "I shoot/stab him", such as TR mentioned with holy water, I'll end up asking you to do a special D20 roll against one of your stats, separate from the combat system.
We can always change shit around if we need too.
EDIT: How about this. If you choose not to take the three shots (and this will apply for melee users too), you can choose to make your called/single shot. This means that you roll for accuracy, and then if you hit roll for damage. The ON TOP of damage dealt, I'll ask you to make a specialized roll (perception for firearms, strength for melee), and if you succeed, you can either:
> Inflict a specialized damage state like stunned or bleeding
OR
> Choose to inflict the extra points past 5 of your strength or perception skill as damage.
.
.
