GG&G, Inc. Beretta 1301 Shotgun Magazine Tube Extension, Includes Barrel Clamp, Removable Endcap, Black GGG-2570 The GG&G Beretta 1301 Magazine Tube Extension provided 2 additional rounds. The 1301 2 Shot Mag Tube is easy to install as long as you have a working knowledge of how to break down your shotgun to perform maintenance procedures. The Beretta 1301 Mag Tube comes with the Beretta barrel clamp. No modification to the shotgun is required.