In December of 1959, Colt acquired manufacturing and marketing rights to the AR-15. In 1962 Colt was able to get the Department of Defense's Advanced Research Project Agency (ARPA) to test 1,000 weapons in its Vietnam-oriented Project Agile. An enthusiastic report led to more studies from the Department of Defense and the Department of the Army, and despite strong Army opposition, Defense Secretary McNamara ordered 85,000 M16's for Vietnam, and 19,000 for the Air Force.

However, early reports showed that the M16 was not living up to expectations. These reports, presented to McNamara by the Ordnance Department, showed the M16 having reliability as well as accuracy problems. These reports in turn praised the Ordnance Department's own M14. While the M14 performed well, it was too heavy for the hot jungles of Southeast Asia, and its ammunition also would not allow more than 50-100 rounds to be carried on patrols, severely limiting its capabilities as an automatic weapon.

Further evaluation of the M14 and M16 was done by an independent agency. It concluded that M14 was not as bad as had been suggested by some, that the AR-15 itself was not as good as its proponents had represented it to be. However, they did note that the AR-15 had greater capability for improvement, and that its small size and weight made it a handier weapon in Vietnam.

The M16 was issued w/o proper training and inadequate cleaning supplies. Combined with the humid jungle of Southeast Asia, this caused problems and the rifle gained a bad reputation. Because tolerances were tighter than in previous military arms, the M16 had to be kept extremely clean. War correspondents filed reports where the M16 was jamming, and many were shown on the evening news. It was reported that our soldiers were being killed by a faulty rifle.

This led to Congressional investigations which turned up two related problems. First, the cleaning issue. As training was provided, supplies issued, and some redesign, M16 performed more reliably. The second issue dealt with the use of ball propellants instead of IMR propellants. Remington had developed the 5.56mm round using one type of powder, but the specification was changed during military contract production to allow an alternate. This powder caused more fouling and increased the rate of fire.

M16A1
The replacement of the powder, combined with a new buffer to slow rate of fire, a chrome plated chamber and barrel to improve rust resistance, a closed prong flash-hider, forward bolt assist, new buttstock w/storage for cleaning kit, and introduction of a 30-shot magazine was adopted as the M16A1 and performed well for the duration of the 60's and 70's. This rifle was also produced by GM and Harington & Richardson during Vietnam era as well as other countries including the Philippines.
M16A2

In the late 1970's, the Army re-examined it's rifle situation. Existing M16s were well worn, and the current programs that were looking into a replacement for the M16 were not far enough along. So in 1978, the M16 underwent a Product Improvement Program. The results were an increased barrel diameter, and one whose rifling was changed from 1:12 to 1:7 to accommodate the new round, developed by Belgium's Fabrique Nationale, the SS109. This round extended the range of the rifle, and propelled a 62gr bullet with a steel core at over 3000 fps. The rear sight was modified to allow more accurate adjustments of windage by hand, as well as for elevation calibrated out to 800 meters. It incorporated a case deflector to prevent brass from hitting left-handed firers, and new round handguards to replace the older triangular design. Also, full-auto capability was replaced with a three-shot burst. This allowed for more controlled firing, as well as greater accuracy as all three rounds are downrange before the effects of recoil can impact their path. This new rifle was adopted as the M16A2.

M4
In 1994, the U.S. Army officially adopted its second carbine of the 20th century. Though carbine versions of the M16 had been used all along (as the XM177 as well as the CAR-15), demand for these was limited to select groups. With the increase in the use of Special Operations forces during and after the Cold War, the demand for a shorter, lightweight weapon was increased. The M4 was developed by Colt's Manufacturing Company, and is intended to be used by Special Operations forces as well as other select members of the military. It is designed to replace a variety of carbines and SMGs in the Army's arsenal, as well as to repeat the accuracy and reliability of the M16A2. It uses a 14.5" barrel, and a four-position telescoping stock while maintaining the ability to mount an M203 grenade launcher. In the collapsed position, it measures under 30 inches, and weights just over 5 1/2 pounds, with an effective range of 600 meters. The M4 is available with 3-shot bursts (M4) as well as full-auto capabilities (M4A1). Both versions of the M4 are equipped with a Picatinny-Weaver Rail system to replace the carry handle. This allows for a variety of sighting systems to be mounted atop the receiver, from the standard handle with A2 sights to night-vision devices, scopes, and lasers.
:assult:

[ScottD]

Hard to believe that it has been around for 45 years. A lot of diferent designs have come and gone and whether you like it or not it has weathered the years just fine.

http://www.globalsecurity.org/milita...ground/m16.htm

Project SALVO

In 1948, the Army organized the civilian Operations Research Office (ORO), mirroring similar operations research organizations in Britain. One of their first efforts, Project ALCLAD, studied body armor and quickly concluded that they would need to know considerably more about battlefield injuries in order to make reasonable suggestions. Over 3 million battlefield reports from WWII were analyzed, and over the next few years they released a series of reports on their findings.

Their basic conclusion was, as was found by the Germans and British before them, that the vast majority of combat takes place at short ranges. In a highly mobile war combat teams ran into each other largely by surprise, and the team with the higher firepower tended to win every time. They also found that the chance of being hit in combat was essentially random -- that is, accurate "aiming" made little difference because the targets no longer sat still. The number one predictor of casualties was the total number of bullets fired.

These conclusions suggested that infantry should be equipped with a fully automatic rifle of some sort, in order to increase the rate of fire. However, it was also clear that such weapons dramatically increased ammunition use, in order for a rifleman to be able to carry enough ammunition for a firefight, they would have to carry something much lighter.

For both of these reasons, existing rifles were poorly suited to real-world combat. Although it appeared the new T44 would increase the rate of fire, its heavy ammunition made carrying enough of it a real problem. Moreover the length and weight of the gun meant it was not really suitable for short range combat, where a smaller and lighter weapon could be brought to bear much more quickly.

These efforts had not gone unnoticed by René Studler, US Army Ordnance's Chief of Small Arms Research and Development. He was upset about the civilian agency that was treading on "his" turf, and started an effort to support the "full power" round developed for the T25. In the end, he asked the Aberdeen Proving Ground to submit a report on the smaller caliber weapons.

This plan backfired when his assigned research lead, Donald Hall, found that a .22 in (5.59 mm) round would have equal performance to larger rounds in most combat situations. With the higher rate of fire possible due to lower recoil, it was likely such a weapon would inflict more casualties on the enemy. His team members, notably William C. Davis Jr. and G.A. Gustafson, started development of a series of experimental .224 in (5.69 mm) rounds. In 1955, their request for further funding was denied.

A new study, Project SALVO, was set up to try to find a weapon design suited to real-world combat. Running between 1953 and 1957 in two phases, SALVO eventually suggested that a weapon firing four rounds into a 20 in (0.5 m) area would have double the hit probability of existing semi-automatic weapons.

In the second phase, SALVO II, several experimental weapons concepts were tested. Irwin Barr of AAI introduced a series of flechette weapons, starting with a shotgun shell containing 32 darts and ending with single-round flechette "rifles". Winchester and Springfield offer multi-barrel weapons, while ORO's own design used two .22, .25 or .27 bullets loaded into a single .308 or .30-06 cartridge.

from http://www.answers.com/topic/m16