The Advanced Combat Rifle program was the U.S. Army's search for a rifle replacement during the 1980s.
The search for an Advanced Combat Rifle (ACR) began in February 1986, during Phase I, with the decision to seek new rifle design for adoption in about 1995. Multi-million-dollar contracts were awarded to six companies; AAI Corporation, Ares, Inc., McDonnell Douglas Helicopter Systems, Colt, Heckler & Koch, and Steyr-Mannlicher. The designers were given free hand within broad limits of weight and size, the primary stipulation being that the rifle had to give 100% improvement in first round hit probability over the then-current M16A2 rifle.
The prototypes developed were:
The McDonnell Douglas and Ares, Inc. weapons were cut from the list before Phase II was started.
Eventually, in 1989, four finalist candidate weapons were tested in Phase III, from Heckler & Koch, Colt, AAI Corporation, and Steyr. Testing was prolonged and expensive, and at the end of it the U.S. Army decided that while all the candidate prototypes showed merit, none of them provided the quantum leap in performance that was desired. The U.S. Army Infantry School issued a report asserting that the M16A2, as a weapon, had already reached its peak, and that the only way to improve first-hit probability was to use an explosive warhead. The program was ended in April 1990, because of it, also leading to the dawn of the Objective Individual Combat Weapon Program.
The various weapon designs in the ACR program are worthy of 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.