The ArmaLite AR-100 was a series of assault rifles derived from the AR-18. It was never adopted, however it led to the Ultimax 100. The weapon was intended to increase firepower of a squad as well as mobility.
The ArmaLite AR100 is a gas operated, 5.56x45mm NATO assault rifle platform fed from 30 round and 100 round drum magazines. Components are interchangable with all weapons with the bolt automatically turns firing pin modes when changed from a closed bolt to open bolt platform. The 100 round drum magazines eject from the magazine insert when empty and discarded during a firefight.
There are 4 variants of the AR-100.
Assault rifle. Fires semi/full auto from closed bolt.
Carbine. Fires semi/full auto from closed bolt.
Carbine. Fires full auto from open bolt and auto ejects magazine when empty.
Light machine gun. Fires full auto from open bolt and auto ejects magazine when empty.