This is the schtick to hit small targets and precise locations.
You know where to hit tough things where it hurts. You always do at least Wound Points equal to the Outcome of the attack. This does not work against vehicles or objects, nor against creatures immune to guns or whose anatomy and weak points you know nothing about.
Whenever the difficulty of the shot is determined by the size of the target, halve the difficulty. You suffer no negative modifiers for stunts that require you to shoot at very small targets; you can shoot a pistol out of the hands of a gunman (make a ranged Disarm at no penalty), or a thrown knife zipping through the air (Actively Defend others as a 1-shot stunt against melee and thrown attacks).
You are also exceptional at non-combat guns stunts. Think of this as a kind of limited telekinesis; if a task can be accomplished with a push or knock in the right direction, you can do it as a gun stunt. Pushing buttons, switching levers, cutting ropes, cutting the wire that disarms the bomb or sending messages by punching them out with bullets in plaster; all are simple tasks for you. Even if such a task would ordinarily use some other skill (such as the bomb wire, above), you can still use your Guns skill. But tasks requiring complex manipulation (unscrewing the lid on a jar) is still out of your realm.
You also get to decide how badly you want to hurt someone when you put them down. When you put a mook down, or when a named character fails a DeathTest caused by one of your Guns attacks, you can elect to merely knock them out. They will awaken in fifteen minutes, still with their accumulated Wound points, but otherwise unhurt and not affecte by any of the results of the failed DeathTest.
This schtick never works with Autofire or any kind of area attack.