In the fireearm world, I often see the terms “caliber” and “cartridge” used incorrectly. Now in and of itself, this is not really a big deal. But when it comes to being technical, we should know what each mean and why they are different. This is especially true when we have anti 2A elements claiming that an AR-15 chambered in .223 is such a large, dangerous “caliber” when in reality it is the one of the smallest “calibers” that is commercially available.

Definition of Caliber

The caliber of a firearm refers to the diameter of the inside of the gun’s barrel, also known as the bore. The caliber determines the projectile size that the gun can fire. It is measured in fractions of an inch (.45 caliber) or in millimeters (9 mm). In reference to the above claim on an AR15, a .223 Remington projectile is not even half the caliber size of a .45 ACP projectile.

Definition of Cartridge

A complete round of ammunition containing bullet, powder, case, and primer. Since the entire cartridge of a .223 Remington is longer in length than that of the previously mentioned .45 ACP, it could be argued that the .223 Remington is indeed a bigger cartridge, but not caliber.