XM and XM177-E2 rifle
Designed a little time after the M16, it was nothing more but a shortened version of the former. With regard to it's era, it was an unbelievably light and easy to handle rifle (just like a sub-machine gun) featuring a range and power almost on par with others full-size assault rifles. Its very, very fast rate of fire was never changed (it could empty a twenty rounds magazine in one second).
It was the weapon of choice of SOG men and most Special Forces as well, together with the AK.