The Experimental Designs of the 1989 American ACR Program
Top to bottom: AAI, Colt, H&K G11, Steyr.
The program sought to increase infantry hit probability. The four entrants tried to achieve this by firing flechettes, duplex ammunition, or shear rate of fire on a burst setting.
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The youtuber the fat electrician did a video about these guns. Informative and funny. ACR program
I believe the Elcan optic on the Colt entry was developed in conjunction with the entry, and while the Colt ACR failed, that Elcan design went on to be the template for their further successful military adopted optics.