AAI ACR (Advanced Combat Rifle)

AAI Advanced Combat Rifle
AAI Advanced Combat Rifle was a part of United States Army program in late 1980s (Photo: AAI)

The AAI ACR was part of the American search for a new assault rifle. The Advanced Combat Rifle (ACR) program began in the early 1980s with the decision to seek a new rifle design for adoption in about 1995.

Advanced Combat Rifle (ACR) Program

Multi-million-dollar contracts were awarded to a number of companies to develop caseless rifle, and, later, further contracts to other companies to examine non-caseless solutions.  The designers were given a free hand within broad limits of weight and size, the primary stipulation being that the rifle had to give 100 percent improvement in first-round hit probability over the current M16A1 rifle.

Under the stress of battle, the average soldier with an M16 may shoot a target at 45 meters, but hit probability is reduced to one out of ten shots on target by 220 meters.

Eventually, in 1989, four candidate weapons were tested, from Heckler & Koch of Germany, Colt and the AAI Corporation of the United States, and Steyr-Mannlicher of Austria. Testing was prolonged and expensive, and at the end of it, the United States Army decided that while all the candidate rifles showed merit, none provided the quantum leap in performance that was desired.

Advanced Combat Rifle (ACR) Program: From top to bottom, ACR test rifles from AAI, HK, Steyr, and Colt
From top to bottom, ACR test rifles from AAI, HK, Steyr, and Colt (Photo: XY)

The program was placed on hold in 1990, and that was that. The expenditure of the program was estimated at approximately US$300 million. However, despite the program ended, the various designs are worth study, because they suggest the way that the next generation of rifles might go, as and when the armies of the world show sufficient interest.


The AAI ACR, compared to some of the others, looks quite conventional; but it actually fires fin-stabilized flechettes, dart-like projectiles, at the high velocity of 4600 feet per second (1400 m/s) and cannot fire conventional ammunition.

AAI Advanced Combat Rifle (ACR) was chambered in 5.56 mm Special
AAI ACR was chambered in 5.56 mm Special (Photo: AAI)

The AAI ACR rifle is driven by a gas piston, and although full details of the breech mechanism have not been revealed, it is said to be derived from an earlier AAI design which, in its most efficient form, used a three-chambered breech unit which moved very quickly in and out of engagement with the barrel to allow very fast cycling of a three-round burst. There is no provision for full-automatic fire.

A four-power optical sight is fitted, with iron sights as a backup, and the muzzle carries a rather unusual compensator/muzzle brake which has been specially designed to work with flechettes.

The barrel is rifled with a very slow twist – one turn in 85 inches – which gives the flechette a degree of roll stabilization and helps accuracy. The flechette idea is not new; several makers, including AAI Corporation, experimented with flechettes as rifle projectiles in the 1960s, but at that time the materials and construction of the flechette cartridge were not particularly good.

Flechette ammunition was used by AAI ACR rifle
Flechette ammunition was used by AAI ACR rifle (Photo: XY)

While the standard 5.56×45mm case was used, the rifle was not safe to fire using standard ammunition due to the design of the gas system. A special magazine was used to prevent soldiers loading standard 5.56×45mm NATO ammunition into the magazine, but rounds could still be chambered by hand. The AAI ACR was limited to three-round bursts despite the fact that one of the main reasons for using a fléchette is its low recoil.

By technology has made the flechette concept more acceptable, the AAI ACR rifle was considered a good design, although not sufficiently accurate for the purpose intended.

Technical specifications: AAI ACR

Manufacturer: AAI Corporation, Baltimore; MD., United States
Type: gas-operated, semi-automatic, and three-round bursts assault rifle
Caliber: 5.56 mm Special
Barrel: 20.6 in (525 mm)
Weight (empty): 7.78 lbs (3.53 kg)
Magazine capacity: 30 rounds
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