When an AKSU met a SAF - both those rather exotic firearms are derivative from the original Kalashnikov assault rifle and seems to demonstrate some kind of Darwin’s finches evolution in space and time.
By Soviet TTT (тактико-технические требования) order number 008407 from 19.17.1973 a design competition (codenamed “Modern"—Модерн) was started for the adoption of a fully automatic carbine, no doubt inspired by observing the US experience in Vietnam with the XM177. The Soviet planners also drew from the unsolicited design AO-46 built in 1969 by Peter Andreevich Tkachev, which weighed only 1.9 kg. The TTT specifications required a weight no greater than 2.2 kg, a length of 75/45 cm with the stock unfolded/folded, and a muzzle velocity of at least 700 m/s. The competition was joined by designs of M.T. Kalashnikov (PP1), I.Y. Stechkin (TKB-0116), S.G. Simonov (AG-043), A.S. Konstantinov (AEK-958), and E.F. Dragunov (who called his model "MA”). Kalashnikov also presented an additional design (A1-75) which differed from PP1 by having a modified muzzle for flash and noise suppression. By 1977 the GRAU decided to adopt Kalashnikov’s model, which was largely a shortened AKS-74, because it was no worse than the competition in terms of performance and promised significant production cost savings by utilizing existing equipment for the AK-74 line. A final round of large scale testing with Kalashinkov’s model was performed by airborne divisions in the Transcaucasian Military District in March 1977. The AKS-74U (“U"—Russian: укороченный; Ukorochenniy, or "shortened”) was officially adopted in 1979, and given the official, but seldom used GRAU designation 6P26.
The SAF is a blowback-operated select-fire gun, firing from a closed bolt. It is based on the Swiss SIG SG 540 assault rifle which was produced under license in Chile in the 1980s. In general the design is a shortened version of the SIG 540 rifle, but the rifle’s rotating bolt has been replaced with a simple blowback bolt. The SAF also has a bolt hold-open catch that engages after the final shot. Otherwise, the receiver, stock, fore-end, trigger/hammer assembly and floating firing pin design are from the SIG 540. The upper and lower receiver, as well as the trigger guard are steel, pistol grip and Handguards are all made from polymer. The ambidextrous safety/fire selector switch, as well as the interchangeability with SIG 552/553 handguards, is a feature found on the latest versions. Older versions used own handguards.