Standard rules apply:
Using a Second Firearm
Characters can use two pistol- or SMG-class weapons, one in each hand. Doing so, however, imposes a +2 target modifier to each weapon and negates any target number reductions from smartlinks, smart goggles or laser sights. Additionally, any uncompensated recoil modifiers applicable to one weapon also apply to the other weapon.
Additionally, Called Shots cannot be made with either weapon, if both weapons are being fired in this combat phase.
In the event that a character is using a Ares Duel Bound Smartlink 2 or similar piece of cyberware designed for this purpose, the +2 penalty is removed and the smartlinks are allowed to work (granting a -2 target number modifier).
Additionally, if the character has a reaction modifier of 8 or greater, he may “fan” the triggers of two semi-automatic pistols to grant a single burst when used versus a single target.