The FAC 70 assault rifle was developed from John Foote's previous rifle prototype, the R68. Foote hand-built the FAC-70 prototype in the US but sent it to England to be evaluated by the Sterling Armament Company, who had expressed an interest in producing a new assault rifle. Ultimately, however, it lost the Sterling contract to the AR-18 from ArmaLite. The FAC 70 prototype remained in the UK in Sterling's archives.
The FAC 70 was essentially an improved version of the R68 that was cheaper and easier to manufacture than the R68. The FAC 70 is also lighter than the R68. Due to similar looks, it can be assumed that the R68 and FAC 70 both used the same AK-derived long stroke gas piston action with a rotating bolt.
As with the R68, for easy usage, the weapon's charging handle was located on top of the weapon so that both left- and right-handed users could use the weapon with ease. The safety was also located inside the trigger guard so that one could flick it quickly while keeping their finger on the trigger. The weapon takes 20 round M16 magazines as standard.