A rifle is a long-barred gun that is capable of shooting accurately at long distances. At one end is a muzzle from which the projectile is launched, and the mechanical components are encased in a stock that lends itself to operating the rifle with the butt, or end of the stock, pressed against the firer's shoulder. The inside of the long barrel has spiral grooves (i.e., rifling) that impart a stabilizing spin to the bullet it fires. Unless otherwise specified, it can be assumed the bullet is propelled by the expanding gases generated by the combustion of an explosive propellant.
Some rifles, usually for sport, may be powered by compressed gas, either air manually pumped to a high pressure, or from a cartridge of carbon dioxide.
Rifles can be single-shot, autoloading, semi-automatic, or full-automatic. Single-shot rifles require manual loading before each firing. While modern rifles combine bullet, propellant, and primer into a single fixed cartridge, early weapons separated these into components that had to be loaded individually. An autoloading rifle does have a magazine that holds multiple cartridges, but it is necessary to manipulate a lever or bolt to eject a fired round and load the next. In contrast, semi-automatic rifles eject, load, and fire with only a trigger action.
While each rifle type is designed to fire one caliber, they group generally into smallbore (.22 caliber or smaller, often anything below .30 caliber/7.62 mm), medium, and large-bore (.50 caliber/12.7 mm or larger).
Battle rifle or infantry rifle fire a full-power cartridge that has longer range than those of an assault rifle (e.g., .30-06 for the M1 Garand rifle or the 7.62x51mm NATO round. These were the standard in the World Wars, but analysis showed that most rifle engagements were fought at short range, and reducing the cartridge size allowed more ammunition to be carried and the rifle to be lighter.
Battle rifles are still deployed to designated marksmen and fully qualified snipers.
The term assault rifle originally had a specific military meaning: a weapon that was semi-automatic or full-automatic, was fed from a large magazine, and fired a medium-caliber rifle cartridge of intermediate propellant power. In legal contexts, the term has sometimes been extended to include rifles with features that are indeed military in intent, such a bayonet mount or a bipod for support. Such additional components, however, were not relevant to the original military designs, which were intended for quickly moving infantry firing suppressive as well as aimed fire.
Carbines are long-barreled individual weapons, at least autoloading, which tend to fire a low-power cartridge, sometimes a cartridge originally designed for pistols. In military practice, carbines are issued to soldiers for whom a longer-barreled rifle would be awkward, such as horse cavalry. The definition has expanded, in recent years, to include shorter weapons of intermediate power, which are easier to handle in situations such as urban combat.