My personal favorite gun right now belongs to an eccentric Dwarf Rigger who goes by the name Hambone. Hambone may be married to his drones, but his mistress is his beloved Bessie, a customized Ruger Super Warhawk.
You start with the Warhawk, then you fill up all six slots with Large Mod Firing Selection Change (to add Full Auto) and High Power Chambering from War (+2 DV, -1 AP). After that, you overmod it to give it a Custom Look, engraving the name 'Bessie' on the side of the barrel.
You now have an 8P, -3AP Revolver that can fire a Long Burst, emptying the cylinder in a single shot and jumping the damage to 13P before net hits. Of course, Hambone applies both his Foot Anchors (+2 recoil comp) and his Cyberarm Gyromount (+3) whenever he fires it, nicely negating the -5 recoil mod from full auto. It's a bitch to reload, but its worth it seeing the look on a ganger's face when you pull this massive mother of gun out of your cyber holster and splatter his chrome troll buddy all over the payment in a single shot.