The projectile (bullet) of a rifle is propelled by the contained deflagration of a combustible propellant compound (originally black powder, later cordite, and now nitrocellulose), though air rifles, which are popular for vermin control, small game hunting, competitive target shooting, and casual sport shooting, use other propulsive means such as compressed air (plinking).

The rifling within a rifle's gun barrel is what distinguishes it from preceding smoothbore long weapons (e.g., arquebuses, muskets).

Lands are elevated portions of a barrel's rifling that make contact with the projectile and impose torque on it as it passes down the bore, spinning it about its longitudinal axis. Buy Rifles for sale online

When the bullet exits the barrel, the spin remains and provides gyroscopic stability to the projectile owing to angular momentum conservation, preventing yawing and tumbling in flight.

This allows for the employment of longer, more aerodynamic bullets (as opposed to the spherical balls used in smoothbore muskets), which enhances range and accuracy.

Machine guns and modern automatic rifles have some design and function overlap. Many light machine guns (like the Russian RPK) are modifications of existing automatic rifle designs.

Light machine guns in the military are usually chambered for the same caliber ammunition as service rifles.

The weight, cooling system, and ammo feed mechanism are the main differences between an automated rifle and a machine gun.

Rifles, unlike machine guns, are incapable of continuous automatic firing due to their lighter components (which overheat fast) and lower capacity magazines; they sacrifice this capability for better mobility.

Magazines are used to feed modern military rifles, although machine guns are usually belt-fed. To avoid overheating, several machine guns enable the user to swiftly swap barrels, whereas rifles do not.

To avoid the risk of "cook-off," most machine guns have an open bolt, but practically all rifles have a closed bolt for accuracy. Machine guns are frequently manned by many soldiers, whereas a rifle is a single weapon.

Larger rifled crew-served weapons firing explosive shells, such as recoilless rifles and naval rifles, are also referred to as "rifles."

Even if the weapon is not rifled, a rifle is referred to in many works of fiction as any weapon with stock and is shouldered before firing or does not fire solid projectiles (e.g., a "laser rifle").

Rifling's beginnings are obscure, however, some of the first practical trials appear to have taken place in Europe during the 15th century. Archers have long known that adding a twist to the tail feathers of their arrows improved accuracy.

Early muskets created a lot of smoke and soot, which had to be cleaned out of the action and bore of the musket regularly, either by bore cleaning or by a purposeful attempt to create "soot grooves" that would allow the firearm to fire more bullets.

Although no one knows for sure, this might have resulted in an apparent improvement in inaccuracy. Many believe the grooved cannon barrel was conceived around 1440 and further refined by Gaspard Kollner of Vienna, Austria, around 1498.

The spirally grooved cannon barrel is thought to have been created in Germany by Augustus Kotter of Nuremberg in 1520. Because rifles were more prone to issues owing to powder clogging the barrel and required longer to reload and fire than muskets, military leaders favored smooth bore weapons for infantry use.

Smoothbore muskets were improved upon by the invention of rifles. Benjamin Robins, an English mathematician, understood in the early 18th century that an extended bullet would preserve the velocity and kinetic energy of a musket ball while cutting through the air with more ease.

Early muzzle-loading rifles' black powder clogged the barrel fast, making loading slower and more difficult. Because the smoke from black powder soon clouded the battlefield and made it nearly hard to aim the weapon from a distance, the rifle's longer-range was thought to be of little practical value.

Because musketeers couldn't afford to pause in the middle of a fight to clean their barrels, rifles were invented limited to use by sharpshooters and non-military uses like hunting.

Muskets were smoothbore firearms with a high caliber and spherical ammunition discharged at a low velocity. The musket ball was a loose fit in the barrel due to the high cost and difficulties of accurate manufacture and the requirement to load quickly from the muzzle.

As a result, when the ball was shot, it bounced off the walls of the barrel and exited the muzzle in an unanticipated trajectory.

The long rifle's balls were smaller, allowing more rounds to be produced for a given amount of lead. These rifles also featured larger barrels with helical grooves, which allowed for greater accuracy.

These initially appeared around 1740, with Jacob Dickert, a German immigrant, being one of the first to do so. There were many such firms in the region by 1850.

The longer barrel was a break from local gunsmiths' German traditions, allowing bullets to travel faster before exiting from the barrel (due to the burning gunpowder being trapped for longer).

The British 95th Regiment (Green Jackets) and 60th Regiment (Royal American), as well as sharpshooters and riflemen during the War of 1812, employed the rifle to great advantage during skirmishing. They were not accepted by the entire army due to their slower loading time than muskets.

Long length was not necessary to circumvent the forward line since rifles were employed by sharpshooters who did not commonly fire over other men's shoulders.

Shorter barrels provided for a more maneuverable weapon, since tight-fitting balls didn't have to be shoved as far down the barrel.

The advent of mini balls in the 1840s solved the problem of sluggish loading, and rifles swiftly supplanted muskets on the battlefield in the 1850s and 1860s.

Many rifles, sometimes known as rifled muskets, were remarkably similar to the muskets they replaced, but the military experimented with different designs as well.

Military forces abandoned muzzleloaders in favor of breech-loading designs in the late 1860s since breech-loading guns proved to have a considerably higher rate of fire than muzzleloaders.

Rifles were primarily single-shot, breech-loading weapons in the late 1800s, meant for directed, discretionary fire by individual troops.

Soon after, Louis-Etienne de Thouvenin designed the Carabine à tige, which had a stem at the bottom of the barrel that deformed and expanded the base of the bullet when pushed, allowing precise contact with the rifling.

The region surrounding the stem, on the other hand, quickly blocked and became filthy.

sometimes known as the "rifled musket," was employed in Japan during the Boshin War (1868–1869).

One of the most notable was the Minié method, which depended on a conical bullet (known as a Minié ball) with a hollow skirt at the base of the bullet and was designed by French Army Captain Claude-Étienne Minié.

When the bullet was shot, the skirt expanded due to the pressure of the bursting charge and gripped the rifling. Because less gas leaked beyond the bullet with a stronger seal, the bullet had more power

A long bullet was also heavier than a spherical ball of the same bore (caliber) diameter.  The greater grip also allowed the bullet to spin more consistently, increasing the range from around 50 yards for a smooth bore to nearly 100 yards.

The expanding skirt of the Minié ball also solved the problem of black powder residue fouling the inside of the barrel, making tight-fitting bullets difficult to load.

Conical bullets could be loaded into rifles just as rapidly as round balls in smoothbores thanks to the Minié method, allowing rifle muskets to take the place of muskets on the battlefield.

Due to their increased power and precision, Minié system rifles, such as the U.S. Springfield and the British Enfield of the early 1860s, played an important role in the American Civil War.

It is more accurate to fire from a prone (i.e., lying down) position than from a standing one because a prone rifleman provides a far smaller target than a standing soldier.

The increased precision and range, paired with lower susceptibility, aided the defense in general, rendering the classic infantry fight between standing and volleying infantry lines obsolete.

It was the first time an infantry rifle with a detachable magazine was used. Christopher Spencer finished the design in 1860.

It employed copper rimfire cartridges that were housed in a seven-round tube magazine that could be removed and fired one after the other. The magazine could be switched for another once it was empty.

An infantryman's weapon is now designed at ranges of 300 meters or fewer, and troops are taught to fire single bullets or bursts of fire at these distances.

In most cases, accurate, long-range firing is the realm of marksmen and snipers in combat, and devoted target shooters in civilian life. At 100 yards, most contemporary marksman rifles and sniper rifles can achieve accuracy of greater than 0.3 mrad (1 arcminute).

The Metford rifling of the Pattern 1888 Lee–Metford army rifle was one extensively manufactured type. Polygonal rifling is still employed in select weapons today, such as the Glock handguns, despite its rarity (which fire standard bullets).

Many of the early designs were prone to dangerous backfiring, which might result in the weapon being destroyed and the person firing it being seriously injured.

(To minimize wear and improve corrosion resistance, many shotguns and small weapons have chrome-lined barrels.)

Because the plating process is complex and might impair the impact of the rifling, this is uncommon on rifles built for great accuracy.) Modern ammunition has a hardened lead core with a softer outer cladding or jacket, which is often made of a copper-nickel alloy.

To further minimize internal friction, some ammunition is coated with molybdenum disulfide — the so-called moly-coated' bullet.

Brass cartridge casings, which expanded in an elastic form at the time of fire and successfully sealed the breech while the pressure was high, then relaxed back enough to allow for simple removal, addressed the problem of appropriate seal creation.

The leading bolt-action design by the end of the nineteenth century was that of Paul Mauser, whose action—wed to a dependable design with a five-shot magazine—became a world standard through two world wars and beyond.

Britain's ten-shot Lee–Enfield and America's 1903 Springfield Rifle versions were similar to the Mauser rifle. Mauser's initial design was closely replicated by the American M1903.

These weapons are most commonly employed to hit key, susceptible targets including computerized command and control vehicles, radio trucks, radar antennas, vehicle engine blocks, and enemy aircraft jet engines.

Anti-material rifles can be used against humans, but the heavier rifle and ammo, as well as the huge recoil and muzzle blast, render them unsuitable for this use.

Although it has a proven kill distance of 2,430 m (1.51 mi) in Afghanistan during Operation Anaconda in 2002, the Barrett M82 is built with a maximum effective range of 1,800 m (1.1 mi). 

An unknown soldier of Canada's elite special operations unit Joint Task Force 1 established the record for the longest verified kill shot at 3,540 meters (11,610 feet).

Using metric units, the formula divides the number of millimeters in a meter (1000) by the barrel twist in millimeters (the length of travel along the barrel per full rotation). This number is then multiplied by the muzzle velocity in meters per second (m/s) and the number of seconds in a minute (60).

For example, using a barrel that has a twist rate of 190 mm with a muzzle velocity of 900 m/s:

This number is multiplied by the muzzle velocity (MV) and the number of seconds in a minute (60). For example, a bullet with a muzzle velocity of 3,000 feet per second (910 m/s) leaving a barrel that twists once per foot (1/12") would rotate at 180,000rpm.

Rifles can be chambered in a range of calibers (bullet or barrel diameters), ranging from 4.4 mm (.17 inch) for varmint weapons to 20 mm (.80 caliber) for the biggest anti-tank rifles.

The breadth of the bullet discharged through the barrel of a rifle is referred to as caliber. Armed forces have long sought for and procured the most devastating and accurate caliber for their weapons.

The standard calibers used by military across the world tend to follow global trends. Throughout the decades of weapon creation and re-design, these tendencies have shifted dramatically.

Muskets were often chambered for large caliber bullets, such as.50 or.59 (12.7 mm or 15 mm), on the assumption that heavier projectiles inflicted more damage.

During World War I and II, most rifles were chambered in .30 caliber (7.62 mm), a combination of power and speed. Examples would be the .303 British Lee–Enfield, the American M1903 .30-06, and the German 8mm Mauser K98.

Detailed study of infantry combat during and after World War II revealed that most small-arms engagements occurred within 100 meters, meaning that the power and range of the traditional .30-caliber weapons (designed for engagements at 500 meters and beyond) was essentially wasted.

The single greatest predictor of an individual soldier's combat effectiveness was the number of rounds he fired. Weapons designers and strategists realized that service rifles firing smaller-caliber projectiles would allow troops to carry far more ammunition for the same weight.

The lower recoil and more generous magazine capacities of small-caliber weapons also allows troops a much greater volume of fire, compared to historical battle rifles.

Smaller, faster traveling, less stable projectiles have also demonstrated greater terminal ballistics and therein, a greater lethality than traditional .30-caliber rounds.

Most modern service rifles fire a projectile of approximately 5.56 mm. Examples of firearms in this range are the American 5.56 mm M16 and the Russian 5.45×39mm AK-74.