What term describes the size of a rifle or handgun bore?

The term that describes the size of a rifle or handgun bore is "Caliber." In firearms terminology, caliber refers to the internal diameter of the barrel or the size of the bullet that is designed to fit through that barrel. It is commonly measured in either inches or millimeters. For example, a .45 caliber handgun has a bore diameter of .45 inches, while a 9mm handgun has a bore diameter of 9 millimeters.

Understanding caliber is crucial for identifying compatible ammunition for a firearm, ensuring proper functioning and safety. This term is widely used when discussing the specifications of handguns and rifles, and it plays a critical role in ballistics, as different calibers can have varying impacts on performance, range, and use.

Other terms like "Gauge" refer specifically to shotguns and indicate the number of lead balls of a certain diameter that weigh a pound, while "Length" and "Type" do not relate specifically to bore size. Thus, caliber is the correct term to describe the bore size of rifles and handguns.