The history of the M16 is long , so I'll try to keep this short.

In 1957 the US Army requested the Armalite division of the Fairchild Aircraft Corp to develop a .22 caliber, select fire, light weight rifle that is capable of penertrating a standard issue combat helmet at 500m. The great Eugene Stoner (a designer at Armalite at the time) using the AR10 rifle(which he designed) as a base design, he began to design and develop this rifle. What he came up with was the AR15 which was released in .223 remington (5.56x45mm).

In 1958 the rifle was issued to the US army for testing, results shown accuracy and reliability problems. 1959 the rights for the design of the AR15 were sold to Colt firearms manufacturing company. 1960 Eugene leaves Armalite and joins Colt. the same year the rifle was demonstrated to the USAF, which later placed an order for 8000 rifles. 1962 The US DOD ARPA purcases 1000 rifles for field trials in south Vietnam, reports about this "black-rifle" were postive. 1963 Colt recieves contracts for 85,000 rifles from the US army (which called it the XM16E1) and a further 19,000 from the USAF. The XM16E1 differed from the AR15/M16 by having an additional device, the so called "forward assist", which was used to manually push the bolt group in place in the case of jams.
1964. US Air Forces officially adopted new rifle as M16. Same year US Army adopted the XM16E1 as a limited standard rifle, to fill the niche between discontinued 7.62mm M14 rifle and the forthcoming SPIW system (which never got past the prototype and trial stages).

1967. US Army adopted the XM16E1 rifle as a standard "US Rifle, 5.56mm, M16A1", on 28 February 1967.

1965 - 1967. Field reports from Vietnam began to look much more pessimistic. M16 rifles, issued to US troops in the Vietnam, severely jammed in combat, resulting in numerous casualties. There were some causes for malfunction. First of all, during the introduction of the new rifle and its ammunition into the service, US Army replaced originally specified Dupont IMR powder with standard ball powder, used in 7.62x51mm NATO ammunition. The ball powder produced much more fouling, that quickly jammed the actions of the M16 unless the gun was cleared well and often. This pitifully combined with the fact that the initial M16 rifles were promoted by the Colt as "low maintenance", so, for the sake of economy, no cleaning supplies were procured for new M16 rifles, and no weapon care training was conducted for the troops. As a result, soldiers did not know how to clean their M16s, and had no provisions for cleaning, and thing soon turned bad. To add the trouble, the ball powders also had a different pressure curve, so they produced higher pressures at the gas port, giving the rise to the rate of fire, and, thus, decreasing accuracy and increasing parts wear.

1967 - 1970. The deficiencies discovered in previous years began do dissolve. 5.56mm ammunition was now loaded using different powders that produce much less residue in the action of the gun. The barrel, chamber and bolt of the rifles were chrome-lined to improve corrosion resistance. Cleaning kits were procured and issued to troops, and a special training programs were developed and conducted ever since. Earliest cleaning kits could be carried separate from rifle only, but since circa 1970 all M16A1 rifles were manufactured with the containment cavity in the buttstock, that held the cleaning kit. At the same time (circa 1970) the new 30 rounds magazines were introduced into service instead of the original 20 rounds ones, to equal Soviet and Chinese AK-47 assault rifles, which had 30-rounds magazines from the very beginning.

The M16 and its variants are still being manufactured and used by many countries.
M16A1
caliber 5.56x45mm M193
action gas operated, rotating bolt
length 980mm
weight(unloaded) 2.90kg
Magazine 20-30rnds STANAG and numerous other magazines.
cyclic rate of fire approx 750 rounds per minute
muzzle velocity approx 945m/s
Max. effective range appox 500m

As a note the when the M16 was used in vietnam most troops never loaded the magazines fully they always left one or two rounds out for reliability reasons.

Personaly the M16 is a good rifle, but It lacks stopping power (especially out at longer distances) and it feels too light to be a real battle rifle.

Most Australian soldiers in vietnam prefered using the 7.62 L1A1 (SLR) instead of the M16, due to the exellent stopping and penetrating power of the 7.62mm round and the reliabilty of the rifle.

I could keep going, but there is alot of history and info about the M16 and its variants and It would take me a day or two to tell you about it.


Enjoy.