FX-05 "Xiuhcoatl" (Fire serpent) assault rifle was developed in Mexico by Directorate of Military Industry (Dirección General Industria Militar Mexicana - DGIM), and was first displayed to public in 2006. The rifle is already in limited production and is issued to Mexican armed forces on limited basis. It is planned to replace older 7.62x51 HK G3 rifles in Mexican service with 5.56mm FX-05 rifles in the coming years. While the FX-05 rifle bears more than passing similarity to the German-made HK G36 rifle, suspicions of the patent infringement from HK were turned down, as the FX-05 does not have any of the patented features of the G36, and have enough internal differences to be considered an original design, although its design is obviously heavily influenced by the German rifle. The FX-05 is currently available in three basic versions - rifle, carbine and short carbine, which differ in barrel length.
The FX-05 "Xiuhcoatl" assault rifle is gas operated, selective fired weapon. Gas piston is located above the barrel, barrel locking is achieved via multi-lugged rotary bolt. Charging handle can be installed on either side of the weapon. Receiver of the rifle is made from impact-resistant polymer, translucent magazines also made from polymer. Safety / fire mode selector switches are located above the pistol grip, on both sides of the gun. Rifle is equipped with integral Picatinny type rail on the top of receiver, and can be fitted either with removable carrying handle / optical sight unit or with detachable iron sights, with protected front post and diopter-type flip-up rear sights. The shoulder stock is also made from polymer; it folds to the right and can be adjusted for the length of pull. When folded, shoulder stock is located below the ejection port on the right side of the receiver, so the gun can be fired with stock folded.