M16A2
M16A2
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Caliber: 5.56×45mm M855
On March 13, 1970, the Pentagon requested other NATO countries to adopt the M16/M16A1 as the NATO standard issue. The British reaction was quite strong. About twenty years ago, the British military strongly opposed the adoption of the 7.62mm T65 cartridge as the NATO standard, arguing that their .280 cartridge was inadequate, and now the Americans were asking them to adopt an even smaller caliber bullet! However, regardless of the objections, the performance of the M16/M16A1 was excellent in the later stages of the Vietnam War, and NATO decided to adopt a new small caliber rifle cartridge as the NATO standard issue.
During the period from April 1977 to spring 1979, NATO conducted a series of tests to determine the new NATO standard issue cartridge. The United States proposed their initial design - the M193, which had no improvements and lacked penetration capability when facing improved individual body armor. The British introduced an improved 5.56mm cartridge, using a slimmer 4.85mm projectile fitted into American cartridge cases. This cartridge had better ballistics and penetration performance, with an effective range of 600m and met the requirements for their squad automatic weapons (light machine guns). The Germans introduced a new 4.7mm caseless cartridge, which was very light and had similar ballistics to the American M193, but the system was prone to self-ignition after extensive firing. The final design came from Belgium, which provided the SS109, a new 5.56mm cartridge with the same dimensions as the American cartridge but with a steel penetrator to improve penetration performance. The muzzle velocity was approximately 3000 feet per second (915m/s), with a longer effective range than the American M193, suitable for use in light machine guns.
The improved M16A1, overseen by the Marine Corps and designated as the M16A1E1, with Colt's model number 645, featured the following improvements over the original M16A1:
- Adopted the Belgian SS109 cartridge, with a rifling twist changed from 1/12 to 1/7, achieving a theoretical rate of fire of 700-900 RPM;
- Increased the outer diameter of the barrel forward of the handguard to 18.5mm, closer to the diameter of the flash suppressor, to improve barrel rigidity, reduce heat buildup during sustained firing, improve single-shot accuracy, and add 170 grams to the barrel weight. The inner diameter of the barrel remained the same as the M16A1 to accommodate the existing M203 grenade launcher (meaning there was no intention to modify or purchase a grenade launcher that could be mounted on a thicker barrel);
- Changed from fully automatic to three-round burst fire to save ammunition;
- Lengthened the stock by 16mm for better ergonomics and durability, making it easier to aim and shoot from the shoulder, and the new stock was more robust;
- Changed the triangular handguard of the A1 to a cylindrical upper and lower handguard, with heat-dissipating ribs on the exterior for improved grip and heat dissipation. The new handguard made it easier for shooters with smaller hands to grip, and the upper and lower halves were fully symmetrical, so there was no need to distinguish between left and right handguards in the armory inventory;
- Increased the diameter of the aperture from 2mm to 5mm for easier target acquisition at close range, changed the shape of the front sight post from cylindrical to square, and made windage and elevation adjustments on the rear sight adjustable, allowing for a sight adjustment range of 300-800 meters to fully utilize the ballistic characteristics of the SS109 cartridge;
- Removed a downward-facing aperture on the flash suppressor to reduce muzzle dust when firing from prone position;
- Added a raised cartridge deflector behind the ejection port to prevent ejected casings from hitting the shooter's face when firing left-handed;
- Changed the material of the stock, handguard, and grip to fiber-reinforced nylon;
- Added a non-slip buttplate to the stock and replaced the straight vertical grip with a finger-grooved grip.
Colt produced a batch of M16A1E1 rifles, designated as the 645 model, and delivered them to the Marine Corps in September 1981. The US Marine Corps conducted thorough testing of the M16A1E1 during the summer of 1981, based on their feedback, Colt further improved the M16A1E1 and finalized the production model as the 701 model in September 1982. The Colt 701
model was officially designated as the M16A2 by the US military, and the Belgian SS109 cartridge produced in the US was designated as the M855, while the L110 cartridge was designated as the M856. However, it was not until a year later, on November 20, 1983, that the M16A2 was officially adopted by the Marine Corps. At that time, some members of the Army were trying to convince the relevant authorities not to adopt the M16A2, although they also acknowledged that a large number of M16A1 rifles were severely worn out after long-term use and training. However, in 1985, the Army still adopted the M16A2.
In 1986, the US Army announced the purchase of 20 million M16A2 rifles for full replacement over an eight-year period (1986-1994). Originally, Colt also participated in the M16A2 improvement program, but when the Army issued a tender for the purchase of 267,000 M16A2 rifles in 1988, Colt lost the production contract for the US Army because its bid was $50 higher than FNMI (the Belgian FN company's manufacturing plant in North America). As a result, the M16A2 rifles equipped by the US military were marked with the FNMI logo. It was not until early 1990 that Colt, after separating from its parent company, finally won a contract to produce 12,000 M16A2 rifles, worth $950,000.
On the issue of production contractors, it is said that senior Army officials did not favor FNMI, a company with foreign background, but the Marine Corps insisted that FNMI's products were of better quality than Colt's. There have been reports on the accuracy of FNMI's M16A2 rifles, with groups of 10 shots within 2 inches at 100 yards during factory acceptance testing. This accuracy is quite high for a service rifle. For example, during World War II, the M1 Garand's factory acceptance testing required groups of 10 shots within 3 inches at 100 yards, while the M16A1 required groups of 10 shots within 4.8 inches at 100 yards. However, according to the acceptance specifications for the M16A2, a dispersion of 4.77 MOA is considered acceptable, and accidental shots are not counted. Results can be averaged over multiple tests. In fact, the accuracy of the M16A2 is slightly worse than that of the M16A1, which is also related to the ammunition, as the M193 is a simple lead-core bullet, while the M855 is a lead-steel composite bullet, which is less consistent in manufacturing. However, some researchers have studied FNMI's acceptance procedures and found that FNMI's M16A2 rifles do have a very high level of accuracy. It is possible that the equipment in FNMI's new factory is better than Colt's old equipment, and the quality management level is high, resulting in stable production quality, so high-quality products can be produced at a low cost. If we liken the acceptance criteria to a passing grade of 60 points, Colt can produce products that just pass the passing line, but FNMI can easily produce high-scoring products.
Acceptance specifications for the M16A2 from the US Army Technical Manual
The M16A2 only has semi-automatic and three-round burst fire capabilities, which cater to the views of some senior Army officers. They believe that three-round bursts are the most suitable (or rather a compromise) solution between saving ammunition, improving hit rate, and enhancing firepower. It is said that British experts also particularly appreciated this firing mode, believing that many poorly trained soldiers do not have the skills to control full-automatic fire, and that "controllable three-round bursts can achieve a higher hit rate than spraying 10 to 15 rounds of bullets at the enemy at once."
However, some American military and technical experts vehemently opposed this. Because this design fundamentally undermines the purpose of a service rifle. The main intention of a service rifle in tactical use is to stop, suppress, eliminate, or intimidate the enemy with sudden and intense firepower. Therefore, after the M16A2 was standardized, there were some variants with full-automatic firing capability, but these full-automatic M16A2 rifles were only used for export, while the standard issue rifles for the US Army and Marine Corps were the three-round burst fire models (Model 645) specified by the US government.
In this matter, Stoner himself also vehemently opposed the initial version of the M16A2. He did not oppose the three-round burst mechanism, but opposed using three-round burst instead of full-automatic fire, as this completely contradicted his original design intention for the M16. As early as the 1960s, a considerable number of American soldiers preferred the semi-automatic firing mode for rifles. The reason was that full-automatic fire wasted ammunition. At that time, Stoner argued persuasively. Many experts found that during World War II, about four-fifths of M1 Garand rifle users did not fire continuously in combat, with soldiers closest to the BAR rifle admiring the spectacle of continuous firing. Therefore, soldiers came to the conclusion that "semi-automatic fire is useless in combat." Stoner believed that even in the hands of a well-trained soldier, a semi-automatic rifle was difficult to wield effectively for several reasons: ① Hesitation in target selection; ② Ceasefire at the first sign of enemy resistance; ③ Dispersed focus when neighboring soldiers are injured or killed; ④ Firing one shot per trigger pull, due to tension or even fear, resulting in shots being either too high or too low. A rifle with full-automatic firing capability was a completely different matter. A soldier holding a rifle like the BAR would feel that he was controlling an area, as long as the enemy was in that area, he could "hose it down" (American military slang describing full-automatic fire).
Furthermore, the three-round
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