A Strongarm's turret.
A revolver turret is part of a revolver-style blaster. It is a five or six shot cylinder that can drop out of the barrel for easy loading, via a switch. Most modders who do mods on revolver-style blasters make the turret drop down all the way, as well as fit the blaster with more than one turret for more ammunition capacity. X-Shot has done a blaster similar to this called the Xcess, which bears resemblance to a Maverick REV-6 with two turrets.