SR4A p.150
Attacker Using a Second Firearm
Characters can use two pistol- or SMG-class weapons, one in each
hand, firing both with a single Simple Action. Doing so, however, requires
that the character split his dice pool between the attacks. If two
separate skills are being used (Pistols and Automatics), use the smallest
dice pool. Split the pool before applying modifiers. Two-gun attacks
also negate any dice pool bonuses from smartlinks or laser sights.
Additionally, any uncompensated recoil modifiers applicable to one
weapon also apply to the other weapon.