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The US Army ACR (Advanced Combat Rifle) program was an effort to find a new type of infantry rifle which could increase the practical accuracy of the M16 by a whopping 100% in the early 1990s. Building on a legacy of similar programs like SALVO and SPIW, the basic idea being tried were extremely high rates of burst fire, flechette rounds, and duplex cartridges as a way to increase hit probability mechanically. There were four final entries into the rifle trials - rifle from AAI, Colt, H&K (the G11), and this rifle from Steyr.
The Steyr ACR entry is a polymer-bodied weapon taking many basic cues from the AUG. It has a low power optic as its primary sighting device, translucent magazines (capacity only 24 round, though), a roughly 1200 rpm rate of fire, and full-hand trigger guard. Mechanically, uses an annular gas piston and fired from an open bolt, with semiauto and 3-round burst modes. The locking system is a unique vertically sliding chamber, using a similarly unique 10gr flechette cartridge with a polymer case and ring primer. It is quite the interesting an unusual rifle...but it failed meet the accuracy standards of the M16, much less substantially improve upon them. In the end, the ACR program was cancelled with none of the entrants meeting the goal.
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