Colt MARS
The Colt MARS (mini-assault rifle system) was an experimental, scaled-down variant of the M16 rifle tested by Colt as a personal defense weapon (PDW) around 1997. It was chambered for the experimental 5.56×30mm MARS cartridge. The 5.56×30mm cartridge fired a  projectile at . The rifle was patented in 1998. See also
Amogh carbine

References

ArmaLite AR-10 derivatives
Assault rifles of the United States
Colt rifles
Personal defense weapons