Firearm A firearm is a device which projects either single or multiple projectile s at high velocity through a controlled explosion . The firing occurs by the gases produced through rapid , confined burning of a propellant . This process of rapid burning is technically known as deflagration . In older firearms , this propellant was typically black powder , but modern firearms use smokeless powder , cordite , or other propellants . Most modern firearms ( with the notable exception of smoothbore shotgun s ) have rifled barrels to impart spin to the projectile for improved flight stability . Background . Beginning around 700 AD , scientists and inventors in ancient China developed different grades of gunpowder and innovated different types of firearms ranging from single shot smooth bore fire lances , multi - barreled guns , multiple launch artillery rockets and the first cannon in the world made from cast bronze . Several centuries later , in late Dark Age Europe , sometimes referred to as the " Middle Ages , " the term " firearm " was used in Old English to denote the arm in which the match was held that was used to light the touch hole on the hand cannon . The term was a variation on the contemporary terms of bow arm and drawing arm still used in archery . Due to the effects of firing the ordnance ( barrel ) at the time , the gunner had to be located somewhat behind the weapon , steadying brace with the other hand , hence the name " hand gun " became synonymous with the " fire arm " . Although the modern term ' gun ' is often used as a synonym for firearm , in specialist or military use it has a restricted sense referring only to an artillery piece with a relatively high muzzle velocity , such as a field gun , a tank gun , or a gun used in the delivery of naval gunfire . Artillery guns are much larger than these firearms , mounted on a movable carriage , having bores of up to 18 inches ( 46 cm ) and possibly weighing many tons . Strictly speaking , such weapons are not firearms . Hand - held firearms , like rifle s , carbine s , pistols and other small firearms are rarely called " guns " in the restricted sense among specialists . Machine gun s fire small caliber ammunition ( generally 14 . 5 mm or smaller ) , and many machine guns are crew served infantry support weapon s , requiring the services of more than one crewman , just like artillery guns . Generally , an automatic firearm designed for a single user is referred to as an automatic rifle . Other terms , including " firearm " itself , have been defined in specialized " ad hoc " ways by various legislation . In recent centuries , firearms have become the predominant weapons used by mankind . Modern warfare since the late Renaissance has relied upon firearms , with wide - ranging effects on military history and history in general . This created a whole new kind of battle , which molded modern - era armies . For handguns and long guns , the projectile is a bullet , or in historical hand cannons , a shot . The shot was initially made from lead already used as ammunition for the sling s , and ironically begun with ballistic shape of a modern bullet , but was rapidly replaced by the cast iron ball . The projectile is fired by the burning of the propellant , but in small arms rarely contains explosives itself as such ammunition is banned by the Hague Convention . The use of expanding ( e . g . hollow - point ) small - arms ammunition in warfare is also banned by the Convention for similar reason ( it aggravates the severity of wounds from small - arms fire ) . For modern artillery the projectile is a shell , which almost always contains explosives , and explosives were also common in older artillery pieces as well . Until the mid - 1800s , projectiles and propellant ( black powder ) were generally separate components used in a muzzle - loading firearm such as a rifle , pistol , or cannon . Sometimes for convenience a suitable amount of powder and a bullet were wrapped in a paper package , known as a cartridge . This evolved into the form of a tubular metal casing enclosing a primary igniter ( primer ) and the powder charge , with the projectile press - fit into the end of the casing opposite the primer . Cartridge ammunition was widely adopted , and as of World War I it had become the primary form of ammunition for small arms , tanks , and artillery . Mortars use a similar concept of encapsulation ; however the projectile and casing are generally a single piece that is launched from the firearm . Some short - range naval guns use cased ammunition , but many battleship and cruiser main guns use a shell and separate bagged powder measures , which are selected according to the desired ballistic path . A distinction is sometimes made between the projectile itself as the weapon and the firearm as a weapons platform . In some cases , the firearm can be used directly as a weapon without firing a projectile , although this is virtually always a secondary method of attack used in close combat . For example , arms such as rifles , muskets , and occasionally submachine gun s can have bayonet s affixed to them , becoming in effect a spear or pike . With some notable exceptions , the stock of a long gun can be used as a club . It is also possible to strike someone with the barrel of a firearm or grasp it by the barrel or grip and strike someone with the butt , which is informally called " pistol - whipping " . A problem for firearms is the accumulation of waste products from the partial combustion of propellants , metallic residue from the bullet itself , and small flecks of the cartridge case , known as fouling or gunshot residue . These waste products can interfere with the internal functions of the firearm . As a result , regularly used firearms must be periodically partially disassembled , cleaned and lubricated to ensure the firearm ’ s reliability . Firearms may sometimes be referred to as small arms . Small arms are firearms which can be carried by a single individual . According to international conventions governing the Laws of War , small arms are defined ( with some exceptions ) as firearms which fire a projectile not in excess of 15 mm ( 0 . 60 inches ) in diameter . Small arms are aimed visually at their targets by hand using either iron sight s or optical sight s . The range of pistols is generally limited to 50 meters , while most rifles are accurate to 500 meters using iron sights , or longer ranges using optical sights . Some purpose - built sniper rifles are accurate to ranges of 2000 m and over . The current record for a successful sniper attack is slightly more than 1 . 5 miles ( 2 . 4 km ) . History . The earliest depiction of a firearm is a sculpture from a cave in Sichuan , China . The sculpture dates to the 1100s and is of a figure carrying a vase - shaped bombard with flames and a cannonball coming out of it . The oldest surviving gun , made of bronze , has been dated to 1288 because it was discovered at a site in modern - day Acheng District , Heilongjiang , China , where the " Yuan Shi " records that battles were fought at that time . The Europeans , Arabs , and Koreans all obtained firearms in the 1300s . The Turks , Iranians , and Indians all got firearms no later than the 1400s , in each case directly or indirectly from the Europeans . The Japanese did not acquire firearms until the 1500s , and then from the Portuguese rather than the Chinese . Small arms . Handgun . The smallest of all small arms is the handgun ( or " pistol " ) . There are three common types of handguns : single - shot pistols ( more common historically ) , revolvers , and semi - automatic pistol s . Revolvers have a number of firing chambers or " charge holes " in a revolving cylinder ; each chamber in the cylinder is loaded with a single cartridge . Semi - automatic pistols have a single fixed firing chamber machined into the rear of the barrel , and a magazine , usually removable , so they can be used to fire more than one round . The Italian - made Mateba revolver is a rare " hybrid , " a semi - automatic revolver . Each press of the trigger fires a cartridge and rotates the cylinder so that the next cartridge may be fired immediately . The British firearms firm Webley & Scott also made an " automatic revolver " around the turn of the 20th century . Handguns differ from rifles and shotguns in that they are smaller , lack a shoulder stock ( though some pistols like the Luger and Browning Hi - Power accept a removable stock allowing its use as a carbine ) , are usually chambered for less - powerful cartridges , and are designed to be fired with one or two hands . While the term " pistol " can be properly used to describe any handgun , it is common to refer to a single - shot or auto - loading handgun as a " pistol " and a revolver as a " revolver " . The term " automatic pistol " is sometimes used and is somewhat misleading in that the term ' automatic ' does not refer to the firing mechanism , but rather the reloading mechanism . When fired , an automatic pistol uses recoil and / or propellant gases to automatically extract the spent cartridge and insert a fresh one from a magazine . Usually ( but not always ) the firing mechanism is automatically cocked as well . An automatic pistol fires one shot per trigger pull , unlike an automatic firearm such as a machine gun , which fires as long as the trigger is held down and there are unspent cartridges in the chamber or magazine . There are , however , some fully automatic handguns ( often referred to as machine pistols ) so , to avoid such ambiguity and confusion , " semi - automatic " , " autoloader " or " self - loading " are preferred when referring to a firearm that fires only one shot per trigger pull . Prior to the 19th century , all handguns were single - shot muzzleloaders . With the invention of the revolver in 1818 , handguns capable of holding multiple rounds became popular . Certain designs of auto - loading pistol appeared beginning in the 1870s and had largely supplanted revolvers in military applications by the end of World War I . By the end of the 20th century , most handguns carried regularly by military , police and civilians were semi - automatic , although revolvers were still widely used . Generally speaking , military and police forces use semi - automatic pistols due to their high magazine capacities ( 10 to 17 or , in some cases , over 25 rounds of ammunition ) and ability to rapidly reload by simply removing the empty magazine and inserting a loaded one . Revolvers are very common among handgun hunters because revolver cartridges are usually more powerful than similar caliber semi - automatic pistol cartridges ( which are designed for self - defense ) and the strength , simplicity and durability of the revolver design is well - suited to outdoor use . Both designs are common among civilian gun owners , depending on the owner ' s intention ( self - defense , hunting , target shooting , competitions , collecting , etc . ) . Handguns come in many shapes and sizes . For example , the " derringer " ( a generic term based on the mid - 19th century " Deringer " brand name ) is a very small , short - barreled handgun , usually with one or two barrels but sometimes more ( some 19th century derringers had four barrels ) that have to be manually reloaded after being fired . Carefully matched single - shot duelling pistol s were used primarily in the 18th and 19th centuries to settle serious differences among " gentlemen " : Alexander Hamilton and Aaron Burr are probably the most prominent Americans who used duelling pistols to settle their differences . Revolvers and auto - loading pistols are produced in a wide variety of sizes , with autoloaders generally categorized as one of four sizes : full - size , compact , sub - compact and ultra - compact . Each size has merits and shortcomings ; a smaller handgun usually sacrifices ammunition capacity , recoil damping and / or long - range accuracy for increased concealability and ease of use by smaller - framed shooters . Fully automatic , relatively easily concealed machine pistol s , such as the MAC - 10 , Glock 18 , and the Beretta 93R , were a late 20th century development . Handguns are small and usually made to be carried in a holster , thus leaving both hands free . Small handguns can be easily concealed , thus making them a very common choice for personal protection . In the military , handguns are usually issued to those who are not expected to need more potent firearms , such as general and staff officers , and to those for whom there is no room for a full - sized rifle , such as vehicle crews . In this last role , they often compete with the carbine , a short , light rifle , which is also usually issued to airborne infantry because of its small size . Handguns were historically issued to riflemen as a secondary weapon , however the reliability and firepower of the modern assault rifle ( and the increasing amount and cost of equipment carried by a soldier ) has made this practice less common as of the end of the 20th century . Outside the military , handguns are the usual armament for police and , where legal , for private citizens . Private citizens in most jurisdictions usually carry only concealed handguns in public except when hunting , since an unconcealed firearm could attract undue attention , and could therefore be less secure . However , 42 States in the US permit open carry of handguns , sometimes subject to licensing or location restrictions . 8 States and the District of Columbia ban open carry outright or restrict it to the point that it is infeasible for everyday practice ( 2 states restrict open carry to rural areas , while 6 others allow it only for outdoor sport such as hunting , or ban it completely ) . 48 US states permit concealed carry , and several states have well over 200 , 000 permit holders . Despite Second Amendment constitutional roots in the United States , the concept of citizens carrying a firearm for self - defense is often a contentious political issue ; see gun politics for more information . Handguns are also used for many sporting purposes and hunting , although hunting usage is usually viewed as somewhat atypical due to the limited range and accuracy of handguns . Some hunters , however , do their hunting in areas of dense cover where long guns would be awkward , or they relish the increased challenge involved in handgun hunting due to the necessity of approaching the game animal more closely . Handgun ammunition is also generally less expensive than rifle cartridges , and is usually sufficient for many larger pest animals such as feral hogs , coyotes and wolves . Small - bore ( e . g . . 22 caliber rimfire ) handguns have long been very popular for competitive target shooting , partially due to the low cost of both the firearms and the ammunition , and there is also a rapidly growing number of sporting competitions for larger calibers , including " practical shooting " , the guidelines of which usually require a handgun of caliber 9x19mm or greater . Long guns . Most modern long gun s are either rifle s or shotgun s . Historically , a long smoothbore firearm was known as a musket . A rifle has a rifled barrel that fires single bullets , while a shotgun fires packets of shot , a single slug , a sabot , or a specialty round ( such as tear gas , bolo shell , or a breaching round ) . Rifles have a very small impact area but a long range and high accuracy . Shotguns have a large impact area with considerably less range and accuracy . However , the larger impact area can compensate for reduced accuracy , since shot spreads during flight ; consequently , in hunting , shotguns are used for flying game . ( See Spreading details ) . Rifles and shotguns are commonly used for hunting and often to defend a home or place of business . Usually , large game are hunted with rifles ( although shotguns can be used ) , while birds are hunted with shotguns . Shotguns are sometimes preferred for defending a home or business due to their wide impact area , multiple wound tracks ( when using buckshot ) , shorter range , and reduced penetration of walls , which significantly reduces the likelihood of unintended harm , although the handgun is also common . There are a variety of types of rifles and shotguns based on the method they are reloaded . Bolt - action and lever - action rifles are manually operated . Manipulation of the bolt or the lever causes the spent cartridge to be removed , the firing mechanism recocked , and a fresh cartridge inserted . These two types of action are almost exclusively used by rifles . Slide - action ( commonly called ' pump - action ' ) rifles and shotguns are manually cycled by shuttling the foregrip of the firearm back and forth . This type of action is typically used by shotguns , but several major manufacturers make rifles that use this action . Both rifles and shotguns also come in break - action varieties that do not have any kind of reloading mechanism at all but must be hand - loaded after each shot . Both rifles and shotguns come in single - and double - barreled varieties ; however due to the expense and difficulty of manufacturing , double - barreled rifles are rare . Double - barreled rifles are typically intended for African big - game hunts where the animals are dangerous , ranges are short , and speed is of the essence . Very large and powerful calibers are normal for these firearms . Rifles have been in nationally featured marksmanship events in Europe and the United States since at least the 18th century , when rifles were first becoming widely available . One of the earliest purely " American " rifle - shooting competitions took place in 1775 , when Daniel Morgan was recruiting sharpshooters in Virginia for the impending American War of Independence . In some countries , rifle marksmanship is still a matter of national pride . Some specialized rifles in the larger calibers are claimed to have an accurate range of up to about one mile ( 1600 m ) , although most have considerably less . In the second half of the 20th century , competitive shotgun sports became perhaps even more popular than riflery , largely due to the motion and immediate feedback in activities such as skeet , trap and sporting clays . In military use , bolt - action rifles with high - power scopes are common as sniper rifles , however by the Korean War the traditional bolt - action and semi - automatic rifles used by infantrymen had been supplanted by select - fire designs known as " automatic rifles " ( see " Automatic Rifle " in the next section ) Automatic weapons . An automatic weapon is a firearm capable of firing multiple rounds with one pull of the trigger . The Gatling gun was an early crank - operated weapon that may have been the first automatic weapon , though the modern trigger - actuated machine gun was not widely introduced until the First World War with the German " Spandau " and British Lewis gun . Automatic weapons are largely restricted to military and paramilitary organizations , though many automatic designs are infamous for their use by organized crime . Automatic firearms have long been available to US civilians , under increasingly restrictive conditions . Importation of machine guns for civilian sale in the US was banned by the Gun Control Act of 1968 . The Hughes Amendment to the Firearm Owners Protection Act now prohibits US civilian ownership or transfer of automatic weapons unless they were registered before 1986 - 05 - 19 . Non - prohibited automatic weapons can be legally transferred to civilians who pay a substantial $ 200 tax to the BATFE , pass a background investigation , and in some jurisdictions get approval from local law enforcement . Permission must be received directly from the BATFE to move a machine gun between states , even if it does not change ownership . An extremely limited number of US citizens have special permits from the BATFE to buy , and even import , automatic weapons produced and registered after 1986 . The use of such weapons is tightly restricted to the film industry under direct supervision of the master of arms holding the permit , and the weapons are often altered so they will not fire " factory " ammunition , but rather only special " light - primer " blank cartridges produced specifically for the film industry . This arrangement allows weapons first produced after 1986 to be used by actors in films and TV series produced inside the US . Machine gun . A machine gun is a fully automatic emplaceable weapon , most often separated from other classes of automatic weapon by the use of belt - fed ammunition ( though some designs employ drum , pan or hopper magazines ) , generally in a rifle - inspired caliber ranging between 5 . 56mm NATO for a light machine gun to as large as . 50 BMG or larger for crewed or aircraft weapons . Although not widely fielded until World War I , early machine guns were being used by militaries in the second half of the 19th century . They were primarily defensive firearms crewed by two men , mainly because of the difficulties involved in moving and placing them , and their inherent lack of accuracy . In contrast , modern light machine gun s such as the FN Minimi are often wielded by a single infantryman . They provide a large ammunition capacity and a high rate of fire with much improved accuracy versus earlier designs , and are typically used to give suppressing fire during infantry movement . Machine guns are also often mounted on vehicles or helicopters , and have often been used since World War I as offensive firearms in fighter aircraft and tanks ( e . g . for air combat or suppressing fire for ground troop support ) . The definition of machine gun is different in US law . The National Firearms Act and Firearm Owners Protection Act define a " machine gun " in the United States code " Title 26 , Subtitle E , Chapter 53 , Subchapter B , Part 1 , § 5845 " as : " . . . any firearm which shoots . . . automatically more than one shot , without manual reloading , by a single function of the trigger " . " Machine gun " is therefore largely synonymous with " automatic weapon " in the US civilian parlance , covering all automatic firearms . Submachine gun . A submachine gun is a magazine - fed firearm , usually smaller than other automatic firearms , that fires pistol - caliber ammunition ; for this reason submachine guns are also commonly called " machine pistols " , especially when referring to handgun - sized designs such as the Škorpion vz . 61 and Glock 18 . Well - known examples are the Israeli Uzi and Heckler & Koch MP5 which use the 9x19mm Parabellum cartridge , and the American Thompson submachine gun which fires . 45 ACP . Because of their small size and limited projectile penetration compared to high - power rifle rounds , submachine guns are commonly favored by military , paramilitary and police forces for close - quarters engagements such as inside buildings , in urban areas or in trench complexes . A related class of firearm is the " Personal Defense Weapon " or PDW , which is in simplest terms a submachine gun designed to fire rounds similar to rifle cartridges . A submachine gun is desirable for its compact size and ammunition capacity , however a pistol round lacks the penetrating capability of a rifle round . Conversely , rifle bullets can pierce light armor and are easier to shoot accurately , but even a carbine such as the Colt M4 is larger and / or longer than a submachine gun , making it harder to maneuver in close quarters . The solution many firearms manufacturers have presented is a weapon resembling a submachine gun in size and general configuration , but which fires a higher - powered armor - penetrating round ( often specially designed for the weapon ) , thus combining the advantages of a carbine and submachine gun . The FN P90 and H & K MP7 are examples . Automatic rifle . An automatic rifle is a magazine - fed long gun , wielded by a single infantryman , that is chambered for rifle cartridges and capable of automatic fire . The Browning Automatic Rifle was the first US infantry weapon of this type , and was generally used for suppressive or support fire in the role now usually filled by the light machine gun . Other early automatic rifles include the Federov Avtomat and the Huot automatic rifle . Later , the German forces fielded the Sturmgewehr 44 during World War II , a light automatic rifle firing a reduced power " intermediate cartridge " . This design was to become the model for the " assault rifle " subclass of automatic weapons . After World War II , the M14 ( a gas - actuated select - fire design that replaced the M1 Garand ) was introduced in the US , followed by the M16A1 assault rifle which was widely used in the Vietnam War . Also soon after World War II , the Automatic Kalashnikov AK - 47 assault rifle was fielded by the Soviet Union and other Communist allies including the Eastern Bloc , China , North Korea , and North Vietnam . Variants of both of the M16 and AK - 47 are still in wide international use today , though other automatic rifle designs have since been introduced . A smaller version of the M16A2 , the M4 carbine , is widely used by US and NATO tank and vehicle crews , airbornes , support staff , and in other scenarios where space is limited . The IMI Galil , an Israeli - designed weapon similar to the AK - 47 , is in use by Israel , Italy , Myanmar , the Philippines , Peru , and Colombia . Swiss Arms AG of Switzerland produces the Sig 550 assault rifle used by France , Chile , and Spain among others , and Steyr Mannlicher produces the AUG , a bullpup rifle in use in Austria , Australia , New Zealand , Ireland and Saudi Arabia among other nations . Loading and firing mechanisms . Muzzle - loaded hand cannon . The original predecessor of all firearms , the hand cannon was loaded with gunpowder and the shot ( initially lead shot , later replaced by cast iron ) through the muzzle , while a fuse was placed at the rear . This fuse was lighted , causing the gunpowder to ignite and propel the cannonball . In military use , the standard hand cannon was tremendously powerful , while also being somewhat useless due to relative inability of the gunner to aim the weapon , or control the ballistic properties of the projectile . Recoil , a principle new to human experience at the time , could only be absorbed by bracing the barrel against the ground using a wooden support , the forerunner of the stock . Neither the amount of gunpowder , nor the consistency in projectile dimensions were controlled , with resulting inaccuracy in firing due to windage , the difference in diameter between the bore and the shot . The hand cannon s were replaced by lighter carriage - mounted artillery pieces , and ultimately the arquebus . Muzzleloader . Muzzle - loading muskets ( smooth - bored long guns ) were among the first small arms developed . The firearm was loaded through the muzzle with gunpowder , optionally some wadding and then a bullet ( usually a solid lead ball , but musketeers could shoot stones when they ran out of bullets ) . Greatly improved muzzleloaders ( usually rifled instead of smooth - bored ) are manufactured today and have many enthusiasts , many of whom hunt large and small game with their guns . Muzzleloaders have to be manually reloaded after each shot ; a skilled archer could fire multiple arrows faster than most early muskets could be reloaded and fired , although by the mid - 18th century , when muzzleloaders became the standard small armament of the military , a well - drilled soldier could fire six rounds in a minute using prepared cartridges in his musket . Before then , effectiveness of muzzleloaders was hindered by both the low reloading speed and , before the firing mechanism was perfected , the very high risk posed by the firearm to the person attempting to fire it . One interesting solution to the reloading problem was the " Roman Candle Gun " . This was a muzzleloader in which multiple charges and balls were loaded one on top of the other , with a small hole in each ball to allow the subsequent charge to be ignited after the one ahead of it was ignited . It was neither a very reliable nor popular firearm , but it enabled a form of " automatic " fire long before the advent of the machine gun . Matchlock . Matchlock s were the first and simplest small arms firing mechanisms developed . Using the matchlock mechanism , the powder in the gun barrel was ignited by a piece of burning cord called a " match " . The match was wedged into one end of an S - shaped piece of steel . As the trigger ( often actually a lever ) was pulled , the match was brought into the open end of a " touch hole " at the base of the gun barrel , which contained a very small quantity of gunpowder , igniting the main charge of gunpowder in the gun barrel . The match usually had to be relit after each firing . Wheellock . The wheellock action , a successor to the matchlock , predated the flintlock . Despite its many faults , the wheellock was a significant improvement over the matchlock in terms of both convenience and safety , since it eliminated the need to keep a smoldering match in proximity to loose gunpowder . It operated using a small wheel much like that on cigarette lighters which was wound up with a key before use and which , when the trigger was pulled , spun against a flint , creating the shower of sparks that ignited the powder in the touch hole . Supposedly invented by Leonardo da Vinci , the Italian Renaissance man , the wheel lock action was an innovation that was not widely adopted . Flintlock . The flintlock action was a major innovation in small arms design . The spark used to ignite the gunpowder in the touch hole was supplied by a sharpened piece of flint clamped in the jaws of a " cock " which , when released by the trigger , struck a piece of steel called the " frizzen " to create the necessary sparks . ( The spring loaded arm that holds a piece of flint or pyrite is referred to as a cock because of its resemblance to a rooster . ) The cock had to be manually reset after each firing , and the flint had to be replaced periodically due to wear from striking the frizzen . ( See also flintlock mechanism , snaphance , miquelet ) The flintlock was widely used during the 18th and 19th centuries in both muskets and rifles . Percussion cap . Percussion cap s ( caplock mechanism s ) , coming into wide service in the 19th century , were a dramatic improvement over flintlocks . With the percussion cap mechanism , the small primer charge of gunpowder used in all preceding small arms was replaced by a completely self - contained explosive charge contained in a small brass " cap " . The cap was fastened to the touch hole of the gun ( extended to form a " nipple " ) and ignited by the impact of the gun ' s " hammer " . ( The hammer is roughly the same as the cock found on flintlocks except that it doesn ' t clamp onto anything . ) In the case of percussion caps the hammer was hollow on the end to fit around the cap in order to keep the cap from fragmenting and injuring the shooter . Once struck , the flame from the cap in turn ignited the main charge of gunpowder , as with the flintlock , but there was no longer any need to charge the touch hole with gunpowder , and even better , the touch hole was no longer exposed to the elements . As a result , the percussion cap mechanism was considerably safer , far more weatherproof , and vastly more reliable ( cloth - bound cartridges containing a premeasured charge of gunpowder and a ball had been in regular military service for many years , but the exposed gunpowder in the entry to the touch hole had long been a source of misfires ) . All muzzleloaders manufactured since the second half of the 19th century use percussion caps except those built as replicas of the flintlock or earlier small arms . Cartridges . A major innovation in small arms and light artillery came in the second half of the 19th century when ammunition , previously delivered as separate bullets and powder , was combined in a single metallic ( usually brass ) cartridge containing a percussion cap , powder , and a bullet in one weatherproof package . The main technical advantage of the brass cartridge case was the effective and reliable sealing of high pressure gasses at the breech , as the gas pressure forces the cartridge case to expand outward , pressing it firmly against the inside of the gun barrel chamber . This prevents the leakage of hot gas which could injure the shooter . The brass cartridge also opened the way for modern repeating arms , by uniting the bullet , gunpowder and primer into one assembly . Before this , a " cartridge " was simply a premeasured quantity of gunpowder together with a ball in a small cloth bag ( or rolled paper cylinder ) , which also acted as wadding for the charge and ball . This early form of cartridge had to be rammed into the muzzleloader ' s barrel , and either a small charge of gunpowder in the touch hole or an external percussion cap mounted on the touch hole ignited the gunpowder in the cartridge . Cartridges with built - in percussion caps ( called " primers " ) continue to this day to be the standard in firearms . In cartridge - firing firearms , a hammer ( or a firing pin struck by the hammer ) strikes the cartridge primer , which then ignites the gunpowder within . The primer charge is at the base of the cartridge , either within the rim ( a " rimfire " cartridge ) or in a small percussion cap embedded in the center of the base ( a " centerfire " cartridge ) . As a rule , centerfire cartridges are more powerful than rimfire cartridges , operating at considerably higher pressures than rimfire cartridges . Centerfire cartridges are also safer , as a dropped rimfire cartridge has the potential to discharge if its rim strikes the ground with sufficient force to ignite the primer . This is practically impossible with most centerfire cartridges . Nearly all contemporary firearms load cartridges directly into their breech . Some additionally or exclusively load from a magazine that holds multiple cartridges . A magazine is defined as a part of the firearm which exists to store ammunition and assist in its feeding by the action into the breech ( such as through the rotation of a revolver ' s cylinder or by spring - loaded platforms in most pistol and rifle designs ) . Some magazines , such as that of most centerfire hunting rifles and all revolvers , are internal to and inseparable from the firearm , and are loaded by using a clip , which is a device that holds the ammunition by the rim of the case and is designed to assist the shooter in reloading the firearm ' s magazine . Examples include revolver speedloader s and the clip used to store rounds for loading into the M1 Garand . In this sense , " magazines " and " clips " , though often used synonymously , refer to different types of devices . Repeating , semi - automatic , and automatic firearms . Many small arms are " single shot " firearms : i . e . , each time a cartridge is fired , the operator must manually re - cock the firearm and load another cartridge . The classic single - barreled shotgun is a good example . A firearm that can load multiple cartridges as the firearm is re - cocked is considered a " repeating firearm " or simply a " repeater " . A lever - action rifle , a pump - action shotgun , and most bolt - action rifles are good examples of repeating firearms . A firearm that automatically re - cocks and reloads the next round with each trigger pull is considered a semi - automatic or autoloading firearm . An automatic ( or " fully automatic " ) firearm is one that automatically re - cocks , reloads , and fires as long as the trigger is depressed . Many modern military firearms have a selective - fire option , which is a mechanical switch that allows the firearm be fired either in the semi - automatic or fully automatic mode . In the current M16A2 , M16A4 and M4 carbine variants of the US - made M16 , continuous fully automatic fire is not possible , having been replaced by an automatic burst of three cartridges ( this conserves ammunition and increases controllability ) . The first " rapid firing " firearms were usually similar to the 19th century Gatling gun , which would fire cartridges from a magazine as fast as and as long as the operator turned a crank . Eventually , the " rapid " firing mechanism was perfected and miniaturized to the extent that either the recoil of the firearm or the gas pressure from firing could be used to operate it , thus the operator needed only to pull a trigger ( which made the firing mechanisms truly " automatic " ) . Automatic rifles such as the Browning Automatic Rifle were in common use by the military during the early part of the 20th century , and automatic rifles that fired handgun rounds , known as submachine guns , also appeared in this time . Submachine guns were originally about the size of carbines . Because they fire pistol ammunition , they have limited long - range use , but in close combat can be used in fully automatic in a controllable manner due to the lighter recoil of the pistol ammunition . They are also extremely inexpensive and simple to build in time of war , enabling a nation to quickly arm its military . In the latter half of the 20th century , submachine guns were being miniaturized to the point of being only slightly larger than some large handguns . The most widely used submachine gun at the end of the 20th century was the Heckler & Koch MP5 . The MP5 is actually designated as a " machine pistol " by Heckler & Koch ( MP5 stands for " Maschinenpistole 5 " , or Machine Pistol 5 ) , although some reserve this designation for even smaller submachine guns such as the MAC - 10 , which are about the size and shape of pistols . Nazi Germany brought the world ' s attention to what eventually became the class of firearm most widely adopted by the military : the assault rifle ( see Sturmgewehr 44 ) . An assault rifle is usually slightly smaller than a battle rifle such as the K98k , but the chief differences defining an assault rifle are select - fire capability and the use of a rifle round of lesser power , known as an intermediate cartridge . This reduces recoil allowing for controllable bursts at short range like a submachine gun , while retaining rifle - like accuracy at medium ranges . Generally , assault rifles have mechanisms that allow the user to select between single shots , fully automatic bursts , or fully automatic fire . Universally , civilian versions of military assault rifles are strictly semiautomatic . Soviet engineer Mikhail Kalashnikov quickly adapted the German concept , using a less - powerful 7 . 62x39mm cartridge derived from the standard 7 . 62x54mm Russian battle rifle round , to produce the AK - 47 , which has become the world ' s most widely used assault rifle . In United States , the assault rifle design was later in coming ; The replacement for the M1 Garand of WWII was another John Garand design chambered for the new 7 . 62x51mm NATO cartridge ; the select - fire M14 , which was used by the US military until the 1960s . The significant recoil of the M14 when fired in full automatic mode was seen as a problem as it reduced accuracy , and in the 1960s it was replaced by Eugene Stoner ' s AR - 15 , which also marked a switch from powerful . 30 caliber cartridges used by the US military up until early in the Vietnam War to the much smaller but far lighter and light recoiling . 223 - caliber ( 5 . 56 mm ) intermediate cartridge . The military later designated the AR - 15 as the " M16 " . The civilian version of the M16 continues to be known as the AR - 15 and looks exactly like the military version , although to conform to BATFE regulations in the U . S . it lacks the mechanism that permits fully automatic fire . Modern designs call for compact weapons retaining firepower . The bullpup design , by mounting the magazine behind the trigger , unifies the accuracy and firepower of the traditional assault rifle with the compact size of the submachine gun ( though submachine guns are still used ) ; examples are the French FAMAS or the British SA80 . Recently , smaller but exceedingly penetrative ammunition types have been introduced , as to allow personal defence weapon s to penetrate ballistic armour . Such designs are the basis for the FN P90 and Heckler & Koch MP7 . Caseless ammunition is another trend ; an example is the German Heckler & Koch G11 . The flechette is yet another improvement over traditional ammunition , allowing for extreme penetration abilities and a very flat trajectory . However , it is gained at the cost of stopping power .