The 5.56 AR18 was developed after the M16 (AR15) by Armalite after they had realized the mistake of selling the rights to the AR15 to Colt.

The AR18 was developed from the original 7.62 NATO AR16 also by Eugene Stoner, in the same way that the AR15 was developed from Stoner's 7.62 AR10.

AR16/18 was designed to be manufactured in a less expensive and more conventional way using stamped steel rather than the then new aluminum used with the 10/15. The 16/18 also included improvements to reliability and used a short gas piston rather than the direct gas system of the AR10/15

Despite the fact that it was probably a better system, like was already written by Keren-Or, it was too late because after much difficulty, the AR15 had just been adopted by the US Army.

Lacking the long field testing and improvements (and exposure) enjoyed by the AR15 that was used by a major customer like the US Army , it's not surprising that the AR18 was not able to later compete on the open market

Interestingly, the AR18's operational system was adopted for the modern H&K G-36 and the British L85 and even the Tavor's mechanism is similar (square bolt carrier and return spring.

It's short piston system is the method used by all the "hot" new M16 improvements like the H&K416, L&W, POF etc.

Sorry for the English... I was a bad student in Hebrew school

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