Also known as dual wielding or double fisting. Many action heroes often wield a gun in each hand for either more firepower or to be able to shoot in multiple directions at the same time. Reloading is another issue. Heroic Bloodshed director, John Woo, pioneered this trope.
The above image is Nicholas Cage wielding a pair of gold-plated M1911 pistols in the John Woo film, "Face/Off"
Examples: ANY John Woo film The Matrix Last Man Standing Max Payne Equilibrium Hellsing Devil May Cry The Shadow Hitman Tomb Raider