Colt M16 The M - 16 Assault Rifle is an Assault Rifle originally developed by Colt in the United States based on the Armalite AR - 15 . It ' s early testing was tough and rigorous , and it was not liked by many in the top branches of the American Military . However , through trial and error , it became one of the most well known assault rifles in the world . Description . The M16 Assault Rifle is the standard issue shoulder weapon in the US military . It marks a departure from normal ballistics in that it uses a smaller , high - velocity round ( 5 . 56mm caliber vs . 7 . 62mm ) . This results in a smaller and lighter weapon as well as smaller ammunition , significantly decreasing combat load . The M16 was effective at ranges of less than 400 – 460 meters , the range within which United States experiences in World War II and Korea had indicated that small arms engagements would occur . The weapon permitted the heavily burdened soldier to maintain the same degree of firepower at a reduced weight . And finally , the M - 16 allowed every soldier to have an automatic fire capability whenever the situation required it , while the weapon ' s lighter ammunition facilitated battlefield resupply in greater quantities , enabling the resupply of field units for longer periods of time . While the M16 possessed less " stopping power " than the M14 . But it was more accurate due to the reduction in recoil stemming from the smaller projectile fired . Both the M16A1 and the AK - 47 rifles were judged far more effective than the M14 in terms of expected casualties per combat load . In general , they produced two times the number of combat casualties that could be produced by the M14 . Thus there was clear evidence of military utility in the M16 rifle , resulting in an increased degree of military advantage accruing to its user . Rifle squads consist of a rifle squad leader and eight soldiers . The rifle squad leader is the senior tactical leader of the squad and controls the squad ' s movement and fires . He conducts squad training and maintains the squad ' s ability to conduct tactical missions successfully . Each infantry squad is further organized into two 4 - man fire teams consisting of a team leader , a grenadier , and an automatic rifleman . The fourth member within each fire team is either the squad ' s antitank specialist or the squad ' s designated marksman . The fire team leader is a fighting leader and leads his team by example . The fire team leader controls the movement of his team and the placement of fires against enemy soldiers . He assists the squad leader as required . The infantry squad fights by fire teams and buddy teams . Firepower is the capacity of a unit to deliver effective fires on a target . Firepower kills or suppresses the enemy in his positions , deceives the enemy , and supports maneuver . Without effective supporting fires the infantry cannot maneuver . Before attempting to maneuver , units must establish a base of fire . A base of fire is placed on an enemy force or position to reduce or eliminate the enemy ' s ability to interfere with friendly maneuver elements . Leaders must know how to control , mass , and combine fire with maneuver . They must identify the most critical targets quickly , direct fires onto them , and ensure that the volume of fires is sufficient to keep the enemy from returning fire effectively , and the unit from expending ammunition needlessly . The M16A1 / M16A2 rifle is the most common weapon fired in built - up areas . The M16A1 / M16A2 rifle and the M249 are used to kill enemy personnel , to suppress enemy fire and observation , and to penetrate light cover . Leaders can use 5 . 56mm tracer fire to designate targets for other weapons . Close combat is the predominant characteristic of urban engagements . Riflemen must be able to hit small , fleeting targets from bunker apertures , windows , and loopholes . This requires pinpoint accuracy with weapons fired in the semiautomatic mode . Killing an enemy through an 8 - inch loophole at a range of 50 meters is a challenge , but one that may be common in combat in built - up areas . When fighting inside buildings , three - round bursts or rapid semiautomatic fire should be used . To suppress defenders while entering a room , a series of rapid three - round bursts should be fired at all identified targets and likely enemy positions . This is more effective than long bursts or spraying the room with automatic fire . Soldiers should fire from an underarm or shoulder position ; not from the hip . When targets reveal themselves in buildings , the most effective engagement is the quick - fire technique with the weapon up and both eyes open . Accurate quick fire not only kills enemy soldiers but also gives the attacker fire superiority . Within built - up areas , burning debris , reduced ambient light , strong shadow patterns of varying density , and smoke all limit the effect of night vision and sighting devices . The use of aiming stakes in the defense and of the pointing technique in the offense , both using three - round bursts , are night firing skills required of all infantrymen . The individual laser aiming light can sometimes be used effectively with night vision goggles . Any soldier using NVG should be teamed with at least one soldier not wearing them . The penetration that can be achieved with a 5 . 56 - mm round depends on the range to the target and the type of material being fired against . The M16A2 and M249 achieve greater penetration than the older M16A1 , but only at longer ranges . At close range , both weapons perform the same . Single 5 . 56 - mm rounds are not effective against structural materials ( as opposed to partitions ) when fired at close range — the closer the range , the less the penetration . For the 5 . 56 - mm round , maximum penetration occurs at 200 meters . At ranges less than 25 meters , penetration is greatly reduced . At 10 meters , penetration by the M16 round is poor due to the tremendous stress placed on this high - speed round , which causes it to yaw upon striking a target . Stress causes the projectile to break up , and the resulting fragments are often too small to penetrate . Even with reduced penetration at short ranges , interior walls made of thin wood paneling , sheetrock , or plaster are no protection against 5 . 56mm rounds . Common office furniture such as desks and chairs cannot stop these rounds , but a layer of books 18 to 24 inches thick can . Wooden frame buildings and single cinder block walls offer little protection from 5 . 56mm rounds . When clearing such structures , soldiers must ensure that friendly casualties do not result from rounds passing through walls , floors , or ceilings . Armor - piercing rounds are slightly more effective than ball ammunition in penetrating urban targets at all ranges . They are more likely to ricochet than ball ammunition , especially when the target presents a high degree of obliquity . The following common barriers in built - up areas stop a 5 . 56 - mm round fired at less than 50 meters : * One thickness of sandbags . Although most structural materials repel single 5 . 56 - mm rounds , continued and concentrated firing can breach some typical urban structures . The best method for breaching a masonry wall is by firing short bursts ( three to five rounds ) in a U - shaped pattern . The distance from the gunner to the wall should be minimized for best results — ranges as close as 25 meters are relatively safe from ricochet . Ballistic eye protection , protective vest , and helmet should be worn . Ball ammunition and armor - piercing rounds produce almost the same results , but armor - piercing rounds are more likely to fly back at the firer . The 5 . 56mm round can be used to create either a loophole ( about 7 inches in diameter ) or a breach hole ( large enough for a man to enter ) . When used against reinforced concrete , the M16 rifle and M249 cannot cut the reinforcing bars . Versions of the M16 . M16A1 . The M16 was initially used by the U . S . Air Force in 1964 . In 1965 , the U . S . Army and U . S . Marine Corps began issuing a different version , the XM16E1 , mostly to forces in Vietnam . In 1967 , it was standardized as the primary assault rifle of the U . S . military as the M16A1 . It had 3 fire modes : Safe , Semi , and Automatic Fire . M16A2 . Entering service in the 1980s , the M16A2 was made to fire the NATO standard 5 . 56mm cartridge . The automatic fire mode of the M16A1 was replaced with a 3 - round burst to avoid wasting ammunition . Other changes included an adjustable - windage rear sight , a case - deflector for left - handed shooters , a slightly longer stock , a heavier barrel , and cylindrical hand guards . The fire selector switch was also switched to the left side of the weapon . The " duckbill " flash suppressor was replaced with the " birdcage " version . M16A3 . A fully - automatic version of the M16A2 , issued solely by the U . S . Navy for use by SEALs and Seabees . The M16A3 is NOT a flat - top version of the M16A2 , as is popularly believed . This confusion stems from Colt ' s use of the A2 and A3 designations for fixed sight and flat - top upper receivers respectively . M16A4 . Retains the M16A2 ' s semi - automatic fire , the carrying handle with the iron sights is now removable to all the attachment of dot sights and scopes . The handguards are also replaced with a Knight ' s Armament M5 Rail Adaptor System for attachment of lights , forward hand grips , laser sights , and other devices . M16 LSW . The Colt M16 LSW is an adaptation of the M16 for the squad support weapon role . M4 carbine . Mechanically the same as the M16A4 , the M - 4 carbine has a shorter barrel and a collapsible buttstock , allowing better maneuvering in tight spaces such as room - clearing . M4A1 Carbine . An M4 carbine with a fully automatic fire mode in place of 3 - round burst for use by Special Operations troops .