Today I invited Dave from the *Blog of Gunz and Shenaniganz* to help me explain some of the basics of bullet sizes which are commonly grouped in Calibers, Millimeters and Gauges. The three major types of ammo. (Pistol, Rifle, Shotgun) Even with the same "caliber" you have different ammo variations. Some of the rifle "twin" sizes. The larger the shotgun ammo "gauge" the smaller the barrel and ammo. And more.