Select fire is the capability of aweapon to be adjusted to fire insemi-automatic,fully automatic, orburst mode.[1] The modes are chosen by means of afire selector switch, which varies depending on the weapon's design. Some select-fire weapons have burst fire mechanisms to limit the maximum number of shots fired automatically in this mode. The most common limits are two or three rounds per trigger pull. Fully automatic fire refers to the ability for a weapon to fire continuously until either the feeding mechanism is emptied or the trigger is released. Semi-automatic refers to the ability to fire one round per trigger pull.[2]
The presence of select fire modes onfirearms permits more efficient use of rounds to be fired for specific needs, versus having a single mode of operation, such as fully automatic, thereby conserving ammunition while maximizing on-target accuracy and effectiveness. This capability is most commonly found on military weapons of the 20th and 21st centuries.
Early attempts at this technology were hindered by one or both of two obstacles: over-powerful ammunition and mechanical complexity. The latter led to excessive weight and unreliability in the firearm.[3] One of the earliest designs dates to just before the end of the 19th century with the development of theCei-Rigotti, an earlyautomatic rifle created by Italian Army officer Amerigo Cei-Rigotti that had select-fire capability (single shots or burst).[4]
Another is theM1918 Browning Automatic Rifle (BAR) developed during theFirst World War. The BAR and its subsequent designs incorporated a variety of select-fire functions. The first design (M1918) is a select-fire, air-cooled automatic rifle that used a trigger mechanism with a fire selector lever that enabled operating in either semi-automatic or fully automatic firing modes. The selector lever is located on the left side of thereceiver and is simultaneously the manual safety (selector lever in the "S" position – weapon is "safe", "F" – "Fire", "A" – "Automatic" fire).[5]: 225–226 The next version (M1918A1) had a unique rate-of-fire reducer mechanism purchased fromFN Herstal with two rates of automatic fire. This reducer mechanism was later changed to one designed by theSpringfield Armory. The final version (M1918A2) provided two selectable rates of fully automatic fire only.[5]: 131–139
DuringWorld War II the Germans began development of the select-fire function which resulted in theFG 42battle rifle developed in 1942 at the request of the German Air Force (Luftwaffe) in 1941.[6] Another German design that used select fire was theStG 44 that was the first of its kind to see major deployment and is considered by many historians to be the first modernassault rifle.[7] "The principle of this weapon -- the reduction of muzzle impulse to get useful automatic fire within actual ranges of combat -- was probably the most important advance in small arms since the invention of smokeless powder."[8]
The select-fire function was later seen in the RussianAK-47 (designed in 1946), the BelgianFN FAL (designed 1947–53) the BritishEM-2 (designed in 1948), and the U.S.AR-10 (designed in 1957) and itsAR derivatives.[9]
Select-fire weapons, by definition, have a semi-automatic mode, where the weapon automatically reloads thechamber after each fired round, but requires the trigger be released and pulled again before firing the next round. This allows for rapid and (in theory) aimed fire.[3] In some weapons, the selection is between different rates of automatic fire and/or varying burst limiters. The selection is often by a small rotating switch often integrated with the safety catch or a switch separate from the safety, as in the BritishSA80 family. Another method is a weighted trigger, such as theSteyr AUG, which will fire a single shot when 4.0 - 7.1 kg (8.8 – 15.4 lbs.) of weight is exerted on the trigger, and then become fully automatic when over 7.1 kg (15.4 lbs.) of weight is applied. This is useful for emergency situations where a rapid volley of rounds is more effective for suppressing a close enemy rather than a single-round burst (multiple single shots with a trigger pull for each round).
Some select-fire weapons offer a burst mode as the second option, where each pull of the trigger automatically fires a predetermined number of rounds (generally two or three), but will not fire any more until the trigger is released and pulled again.[3] The current U.S. standardassault rifle, theM16A4, and theM4 carbine variant of this rifle fire a maximum of three rounds with each pull of the trigger inburst mode. In this design, it retains the count of previously fired rounds and may fire fewer than three rounds. Other designs reset the count with each trigger pull, allowing a uniform three-round burst as long as rounds remain.
A common version of theHeckler & Koch MP5submachine gun (which is widely used bySWAT teams andmilitary special operations personnel) fires single shots, three-round-bursts, and automatically. A special variant uses a two-round-burst to minimize the chances of missing with a third round. Some automatic cannons have larger burst limiters to coincide with higher rates of fire.