Steyr ACR

The Steyr ACR was a prototype flechette-firing "assault rifle" built for the US Army's Advanced Combat Rifle program of 1989/90. Although the Steyr design proved effective, as did most of the weapons submitted, the entire ACR program ended with none of the entrants achieving performance 100% better than the M16A2, the baseline for a successful ACR weapon.

Design
The Steyr ACR has some superficial resemblance to the Steyr AUG, although it is rounder and the barrel is covered for almost its entire length, as opposed to the AUG where much of the barrel was exposed. Like the AUG the ACR is a bullpup design with the 24 round magazine located quite close to the buttstock of the gun. The stock was "split" from the magazine forward to a location just below the sights to open for cleaning. An optical sight was included as a standard feature.

Ammunition
The ACR's rounds were unique, and the weapon's most interesting feature. Each flechette was packaged along with gunpowder and three plastic sabots inside a cylindrical plastic package with a ring of primer wrapped around the cylinder near the base of the bullet. The mechanism for firing these rounds was also unique; instead of driving rounds forward into the chamber and being held in place by a locking bolt, the entire chamber traveled vertically the width of the round. After firing the gasses "blew" the chamber vertically downward where a new round was forced into the chamber from the rear, forcing the old round out an ejection port ahead of the magazine. Springs then raised the chamber back into position where it was locked into a fixed block. The firing pin was fixed above the chamber, entering through a small hole and striking the ring of primer to fire. The chamber was normally held in the "down" position, the trigger releasing it to allow the springs to drive it upward and fire.

Performance
During testing the weapon performed well, and only two problems were identified. One was that the plastic casings had varying strengths, which has some effect on the ballistics. This was considered to be a fairly minor problem, one they expected could be solved through better materials and quality control. The other issue was somewhat more difficult to solve; when the sabots left the barrel they were still going quite fast, and presented a danger to other soldiers as well as to the shooter if they bounced off the ground when firing prone. There is potentially a third problem in that the gun ejects hot magazine cartridges downwards into an area usually occupied by a person's wrist, possibly causing serious burns if the shooter is not wearing combat gloves. A build up of hot gases might occur just below the shooter's face if the gun was fired while prone, again causing potential minor burns.