Advanced Combat Rifle
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The Advanced Combat Rifle was a US Army program to find a replacement for the venerable M16 assault rifle. Phase I of the program started in February 1986 when development contracts were placed with six companies: AAI, ARES, Colt, HK, McDonnell Douglas Helicopter Company (MDHC), and Steyr.
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[edit] Phase I
Two weapons were cut from the list before Phase II started. The companies started an appeals process and were eventually re-instated, but too late to see testing before the ACR program ended.
[edit] Ares
Eugene Stoner’s ARES Incorporated also entered their Advanced Individual Weapon System (AIWS), which used a 5mm tracer round, but had to withdraw due to ongoing problems. The AIWS shares some features with the Steyr entry, notably the “rising block” action and “telescoped” cartridge.
[edit] MDHC
McDonnell Douglas Helicopter, originally Hughes Aircraft, planned to enter their design using a plastic-cased cartridge they called a chiclet due to its box-like profile. Their first loads used duplex or triplex loads of normal projectiles, but the recoil was too high so these were replaced with flechettes, first with five of them in a .42 round, eventually three in a .338 round.
[edit] Phase III
Phase III, began in August 1989, when AAI, Colt , HK, and Steyr entered weapon testing. Although all the designs worked well, none managed to meet or even approach the 100% improvement over the M16A2 that the program demanded. In 1986/7 the U.S. Army Infantry School had published a report asserting that the rifle, as a weapon, had already reached its peak, and the only way to really improve matters was to use an exploding warhead. This led to the ending of the ACR program in April 1990, and led the way to the Objective Individual Combat Weapon program. The ACR program was preceded by older programs such as the Special Purpose Individual Weapon.
[edit] AAI
AAI entered the latest variant of their long line of so-far unsuccessful flechette rifles. Their entry used a 5.56 x 45 mm round weighing 9.1 grams firing a 1.6 x 41.27 mm flechette of 0.66 grams at 1402 m/s. One of the biggest complaints about their earlier efforts was the loud sound, a problem that is hard to avoid with a sabotted round, so for this version they added a well developed flash hider/noise suppressor that made it just louder than an M16A2. A new magazine was used to avoid soldiers loading standard ammunition into the clips, but rounds could still be chambered by hand and this presented a potential problem. Oddly the weapon was limited to three-round bursts, because one of the main reasons for using a flechette is that its light weight makes very high cyclic speeds possible due to low recoil. This particular design was less advanced than some of their earlier models, which could switch between flechette ammunition for rapid fire and standard 5.56 NATO rounds for long-range semi-automatic fire.
[edit] Colt
One of the more traditional of the ACR prototypes was the Colt ACR, which was a highly modified version of the existing M16A2. The main external modifications were the addition of a new optical sighting system, a buffer to smooth out recoil during automatic fire, and a collapsing butt stock similar to the one already in use on the carbine versions of the M16. The key internal improvement was the use of "duplex rounds", a single cartridge with two smaller bullets in it. Olin produced three different rounds for testing, the first consisting of two tungsten projectiles in a long-necked round, the second a standard-length case with two 27 grain (1.75 g) 0.158-inch (4 mm) tungsten projectiles, and the final entry was another long-necked round with two 0.224-inch (5.69 mm)rounds, one 35 grains (2.27 g)the other 33 (2.14 g). The basic idea of the duplex load is to increase the rate of fire, which is the primary determinant of battlefield casualties. However they also significantly reduce accuracy, requiring the user to pack two types of ammunition for long-range shots. Since the Colt ACR used non-standard length cartridges, this would have meant having to produce new "singlex" rounds as well.
[edit] HK
One of the most distinctive, and well known, of the ACR entries was the Heckler & Koch G11, in a new version known as the G11 K2. The G11 series used a caseless ammunition where the gunpowder was molded onto the bullet itself, making the round smaller and much lighter. Unfortunately it was later realized that the brass casing normally used carries away a considerable amount of the heat of firing, and without the casing the early model G11's tended to overheat and eventually "cook off" their ammunition. By the time of the ACR contest these problems had been fixed. The new K2 version held 45 rounds in a single long clip lying along the top of the barrel, leading to a distinctive and somewhat blocky appearance.
[edit] Steyr
The final entry was the Steyr ACR, another flechette-firing weapon. The Steyr differed from the AAI in the details of the round, which used a plastic shell casing to reduce weight. The firing mechanism was quite complex as a result, moving the entire chamber as opposed to just the block. When fired, the chamber would move down where a new round is pushed in from the rear and forced the old round out of a hole in the front of the rifle. The chamber would then move back into firing position on a spring, where it would lock in front of a fixed block. On firing the sabots travelled down the barrel with the flechette and were quickly "stripped" off on exiting. This was found to present a hazard in combat, where the sabots could hit other soldiers or bounce off the ground when being fired prone. Like the AAI weapon, the Steyr was also limited to three round bursts.
