Science Fair Project Encyclopedia
A rifle is any long gun which has a rifled barrel. A rifled barrel incorporates two or more helical grooves in its bore which impart a spin upon the projectile (usually a bullet) as it travels down the barrel. The angular momentum thereby imparted to the projectile partially insulates it from certain aerodynamic forces which would otherwise cause it to deviate more substantially from a straight path. The consequent gyroscopic stability allows for much greater accuracy, and therefore, effective range, than would otherwise be attainable through the use of a non-rifled barrel, such as that in a musket or shotgun.
Originally, rifles were sharpshooter weapons, whilst the regular infantry made use of the greater firepower of massed muskets, which fired round balls of calibres up to 0.75 inch (19 mm). Benjamin Robins, an English mathematician, realised that an extruded bullet would retain the mass and kinetic force of a musket ball, but would slice through the air with much greater ease. The innovative work of Robins and others would take until the end of the 1700s to gain acceptance.
By the mid-1800s, however, manufacturing had advanced sufficiently that the Brown Bess was replaced by a range of - generally single-shot, breech-loading - rifles, designed for aimed, discretionary fire by individual soldiers. Then as now, rifles have a stock, either fixed or folding, which is braced against the shoulder. Until the early 1900s rifles tended to be very long - a Martini-Henry of 1890 was almost six feet (1.8 m) in length, with a fixed bayonet - and the demand for more compact weapons for cavalrymen led to the carbine, or shortened rifle.
Some manufacturers make rifled shotguns.
History of design
Muskets were smooth-bore, large caliber weapons using ball-shaped ammunition fired at relatively low velocity. Because of the high cost and great difficulty of precision manufacturing, the ammunition generally did not fit tightly in the barrel. The origins of rifling are difficult to trace, but some of the earliest practical experiments seem to have originated in Europe during the fifteenth century. Archers had long realised that a twist added to the tail feathers of their arrows gave them greater accuracy. Early muskets produced large quantities of smoke and soot, which had to be cleaned from the action and bore of the musket frequently; either the action of repeated bore scrubbing, or a deliberate attempt to create 'soot grooves' might also have led to a perceived increase in accuracy, although no-one knows for sure. True rifling dates from the mid-1400s, although the precision required for its effective manufacture kept it out of the hands of infantrymen for another three and a half centuries.
Some early rifles were created with special barrels that had a twisted polygonal shape. Specially-made bullets were designed to match the shape so the bullet would grip the rifle bore and begin to spin. They generally remained large caliber weapons and the ammunition still did not fit tightly in the barrel. Many experimental designs used different shapes and degrees of spiralling. Although uncommon, polygonal rifling remains today; the popular GLOCK pistols have polygonal rifling, for example.
These designs were gradually replaced with cylindrical barrels cut with helical grooves, the surfaces between the grooves being called "lands". This innovation shortly preceded the mass adoption of breech-loading weapons, as it was not practical to push an overbore bullet down through a rifled barrel, only to then (try to) fire it back out. The dirt and grime from prior shots was pushed down ahead of a tight bullet or ball (which may have been a loose fit in the clean barrel before the first shot), and, of course, loading was far more difficult, as the lead had to be deformed to go down in the first place, reducing the accuracy due to nose deformation. Several systems were tried to deal with the problem, usually by resorting to an underbore bullet that expanded upon firing. One of the most famous was the Miniť system, which relied on a conical bullet (known as a Minie bullet or Miniť ball) with a hollow at the base that would expand and grip the rifling as the round was fired. Miniť system rifles, notably the U.S. Springfield and the British Enfield of the early 1860s, featured prominently in the U.S. Civil War, due to the enhanced power and accuracy. The better seal gave more power, as less gas escaped past the bullet, which combined with the fact that a longer bullet of the same diameter could weigh a lot more than a round ball for the same barrel bore or caliber. Enhanced accuracy came from the expansion to grip the rifling, which spun the bullet more consistently.
Another important area of development was the way rounds were stored and used in the weapon. The Spencer repeating rifle was a breech-loading manually operated lever action rifle, that was adopted by the United States and used during the civil war, with over 20,000 made. It marked the first adoption of a removable magazine-fed infantry rifle by any country The design was completed by Christopher Spencer in 1860 and it used copper rimfire cartridges stored in a removable seven round tube magazine, enabling the rounds to be fired one after another, and which, when emptied could be exchanged for another.
As the bullet enters the barrel it screws itself into the rifling, a process which gradually wears down the barrel, and more rapidly causes the barrel to heat up. For this reason machine-guns are equipped with quick-change barrels which can be swapped every few thousand rounds, or, in earlier designs, were water-cooled. Modern stainless steel barrels for target rifles are much harder, and so wear far less, allowing tens of thousands of rounds to be fired before accuracy drops, unlike older carbon steel barrels, which were more limited, to around 1,000 shots, before the extreme accuracy faded. (Many shotguns and small arms have chrome lined barrels to reduce wear and enhance corrosion resistance. This is rare on rifles designed for extreme accuracy as the plating process is difficult and liable to reduce the effect of the rifling.) Hardened armour-piercing bullets produce wear rapidly, which necessitates that they are encased in softer metal or teflon.
Over the 19th century, bullet design also evolved, the slugs becoming gradually smaller and lighter. By 1910 the standard blunt-nosed bullet had been replaced with the pointed, 'spitzer' slug, an innovation which increased range and penetration. Cartridge design evolved from simple paper tubes containing black powder and shot to sealed brass cases with integral primers for ignition, whilst black powder itself was replaced with cordite, and then other smokeless mixtures, propelling bullets to higher velocities than before.
The increased velocity meant that new problems arrived, and so bullets went from being soft lead to harder lead, then to copper jacketed, in order to better engage the spiralled grooves without being "stripped" in the same way as a thread would be if subjected to extreme forces.
Rifles were initially single-shot, muzzle-loading weapons. During the 18th century, breech-loading weapons were designed, which allowed the rifleman to reload whilst under cover, but defects in manufacturing and the difficulty in forming a reliable gas-tight seal prevented widespread adoption. During the 19th century, multi-shot repeating rifles using lever, pump or linear bolt actions became standard, further increasing the rate of fire and minimising the fuss involved in loading a firearm. The problem of proper seal creation had been solved with the use of brass cartridge cases, which expanded at the point of firing and effectively sealed the breech while the pressure remained high, that shrinking back slightly to allow for easy removal. By the end of the 19th century, the leading bolt-action design was that of Paul Mauser, whose action - wedded to a reliable design possessing a five-shot magazine - became a world standard through two world wars and beyond. The Mauser rifle was paralleled by Britain's ten-shot Lee-Enfield and America's 1903 Springfield rifle models, the latter of which is pictured above.
The advent of mass, rapid firepower and of the machine-gun and the rifled artillery piece was so rapid as to outstrip the development of any way to attack a trench filled with rifle and machine-gun equipped soldiers. The nightmare hell of the Great War was to be the greatest vindication and vilification of the rifle as a military weapon. By the Second World War military thought was turning elsewhere, towards more compact weapons. These designs became the assault rifle, one of the most significant developments of the 20th century army.
Nonetheless, civilian rifle design has not significantly advanced since the early part of the 20th century. Modern hunting rifles have fiberglass stocks and more advanced recoil pads, but are fundamentally the same as infantry rifles from 1910. Many modern sniper rifles can trace their ancestry back for over a century; the Russian 7.62 x 54 mm bullet, used in the front-line SVD Dragunov, dates from 1891.
WW2 saw the first mass-fielding of self-loading, semi-automatic rifles including the M1 Garand. As machine-gun mechanisms became smaller, lighter and more reliable, fully-automatic rifles and assault rifles became the norm.
History of use
Muskets were used for rapid, unaimed volley fire. The rifle was originally a sharp-shooter's weapon used for targets of opportunity and sniper fire. In the early part of the 20th century, soldiers were trained to shoot accurately over long ranges with high-powered cartridges. WW1 Lee-Enfields and several other rifles were equipped with long-range 'volley sights' for massed fire at ranges of up to a mile (1600 m) - individual shots were unlikely to hit, but a platoon firing repeatedly could produce an effect similar to artillery - but experience in WW1 showed that long-range fire was best left to artillery and machine guns.
Up to, during, and after WW2 it has become accepted that most infantry engagements took place at ranges of less than 100 metres, and that the range of power of old military rifles was 'overkill'. Today, an infantryman's rifle is optimised for ranges of 300 meters or less, and soldiers are trained to deliver individual rounds or bursts of fire at these ranges. Accurate, long-range fire is the domain of the sniper and of enthusiastic target shooters. The modern sniper rifle is generally capable of accuracy greatly below that of one minute of angle.
In recent decades large-calibre anti-materiel sniper rifles, typically firing Browning .50 (12.7 mm) heavy machine gun rounds, have been developed. The Barrett M82A1 used by the United States is probably the best known such rifle. These weapons are typically used to strike critical, vulnerable targets such as radar antennae or the jet engines of enemy aircraft. Anti-materiel rifles can certainly be used against human targets, but the much higher weight of rifle and ammunition, and the massive recoil and muzzle blast, make them impractical for such use.
The Barrett M82 is credited with a maximum effective range of 1800 metres (1.1 mile). The longest ranges possible with rifled weapons are reached with artillery pieces, a typical 155 mm NATO howitzer being capable of hitting an area at a distance of up to 30 kilometres, depending on the ammunition.
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