Special reload completely reloads Combat Shotgun (not +1 ammo simple reload gives), over-charges energy weapon and allows you to reload both guns when dual-wield
Since everyone loves the spoiler tags:
Pick two levels of Son of a gun to unlock the Dualgunner skill. You can dual wield pistols (and only pistols) by putting a second pistol in your prepared slot. You'll always fire both guns when attacking unless the second one is empty. Normal reload only reloads the primary weapon, special reload reloads both at double the reload time(24)