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The Colt MARS is an experimental, scaled down version of the M16 rifle tested by Colt's Manufacturing Company as a personal defense weapon (PDW) in the 1990s. It was chambered for the experimental 5.6x30 MARS cartridges.
This was tested along with the SCAMP Machine Pistol. The 5.6 cartridges were 55Gr. and fired at ~2600 ft/s. The rifle was patented in 1998, patent no. #5,827,992.