Caliber in small arms, the internal diameter of a firearm's barrel or a cartridge's bullet, usually expressed in millimeters or hundredths of an inch; in measuring rifled barrels this may be measured across the lands or grooves or; a specific cartridge for which a firearm is chambered, such as .44 Magnum. In artillery, the length of the barrel expressed in terms of the internal diameter.
Carbine is a shortened version of a service rifle, often chambered in a less potent cartridge or; a shortened version of the infantryman's musket or rifle suited for use by cavalry.
centerfire: a cartridge in which the primer is located in the center of the cartridge case head. Unlike rimfire cartridges, the primer is a separate and replaceable component. The centerfire cartridge has replaced the rimfire in all but the smallest cartridge sizes. Except for low-powered .22 and .17 caliber cartridges, and a handful of antiques, all modern pistol, rifle, and shotgun ammunition are centerfire.
COL (cartridge overall length): This is the maximum overall length the cartridge can be – and – expected to function properly in magazines and the mag well of a bolt-action rifle.
CQB: close-quarters combat or close quarters battle is a type of fighting in which small units engage the enemy with personal weapons at very short range, potentially to the point of hand-to-hand combat or fighting with hand weapons such as swords or knives.