Seeking to upgrade their supplies of standard-issue HK G3A3 series assault rifles, Mexican authorities centered in on the HK G36 system. The original G3 appeared in 1959 and went on to see widespread use with a host of countries and in countless conflicts. The system relied on the 7.62x51mm NATO cartridge and fired through a roller-delayed blowback action from a 20-round detachable box magazine. A 50-round drum could be affixed for the squad automatic weapon role. The G36, on the other hand, represented a much more modern solution from the same German Heckler & Koch firm. It was introduced in 1997, fired the 5.56x45mm NATO cartridge from a gas-operated/rotating bolt action and was compatible with a 30-round box magazine or 100-round "C-Mag" drum. The Mexican government and Heckler & Koch had agreed to a locally-produced version of the G36 in which factories would be built directly in Mexico under license.
At some point, it was determined by Mexican authorities that it would make more fiscal sense in the long run to design, develop and produce an indigenous assault rifle system. As such, the HK G36 initiative fell to naught and work began on developing a suitable modern replacement for the outgoing HK G3 models. The result became the FX-05 which is entirely constructed from local resources. it represents a drastic departure for the Mexican military and security forces who had relied on importation of foreign weaponry for decades before the arrival of the indigenous FX-05. The FX-05 subsequently entered service in 2008 and has seen considerable action in the Mexican drug wars to date. Manufacture of the FX-05 is handled by the Direccion General de Industria Militar del Ejercito (DCIME).
The FX-05 is a conventional assault weapons design with very clean looks and modern styling. Lightweight polymers are utilized alongside metal parts to keep the overall weight of the weapon as manageable as possible while also making for a reasonable firing platform. The frame is a large, stout piece of engineering that includes the receiver and an integrated forend around the barrel assembly base. The buttstock is semi-skeletal and can fold over the receiver for a more compact approach and sports a rubber pad. The pistol grip integrates well into a large trigger guard for access with a gloved hand. The magazine feed is fitted just ahead of the trigger unit and supports a curved 30-round box magazine made up of 5.56x45mm NATO cartridges. The firing action is gas-operated with a rotating bolt and allows for a cyclic rate-of-fire of 750 rounds-per-minute to be reached. Muzzle velocity is 3,136 feet per second. A selector switch along the sides of the receiver allow for single-shot semi-automatic fire, three-round burst capability or full-automatic fire as well as a safety mode. Iron adjustable sights are standard though optics are often times utilized - the standard optics system also doubles as the carrying handle along the top of the receiver. The FX-05, like other modern automatic weapons of this class, makes heavy use of Picatinny rails for the installation of accessories including standard telescopic sights, night vision, laser aimers, flashlights and the like. Rails are noted along the full length upper portion of the receiver and along the sides of the forend/handguard. There are cooling slots located above the handguard which encompasses the barrel. There is also a slotted muzzle brake. The barrel itself is cold forged and, a distinct feature to the FX-05, is its use of polygonal rifling as opposed to the widely-accepted normal grooved rifling. Support for an underslung single-shot grenade launcher (the HK AG36 for the interim) is noted.
To the discerning viewer, the FX-05 certainly does share a visual similarity to the HK G36 rifle the Mexican Army nearly acquired for license production. In fact, the similarities were such that representatives of Heckler & Koch flew to Mexico to inspect the FX-05 for possible patent infringement. HK representatives walked away satisfied that the FX-05 only mimicked the external appearance of their G36 product, the internal working components being unique to the Mexican FX-05. However, it is worth noting that a "second generation" FX-05 has since appeared that sports a revised receiver. HK officials did not the close appearance of their G36 receiver to that of the original FX-05 production models. Regardless, no law suit ensued and the FX-05 remains in growing numbers within the Mexican Army inventory.
To date, some 50,000 FX-05 examples have been produced. A companion single-shot grenade launcher is currently in the works and will be able to utilize "smart" grenade munitions. The FX-05 has been further developed into forms beyond the basic assault rifle which now makes up the head of a family of firearms. As such, the FX-05 is available in a shortened carbine form, a light machine gun for the squad automatic weapon role and a "sharpshooter" system allowing for repeating fire in the designated marksman role.
The FX-05 is nicknamed the "Xiuhcoatl" which translates to "Turquoise Serpent" or "Fire Snake".