FX - 05 Xiuhcoatl The FX - 05 " Xiuhcoatl " ( literally , " turquoise - serpent " in Classical Nahuatl ; metaphorically or descriptively , " fire serpent " ) is a Mexican assault rifle , designed and built by the " Dirección General de Industria Militar del Ejército " ( Directorate General of the Army Military Industry ) . The rifle was officially presented in the military parade on September 16 , 2006 , in the hands of the Special Forces Airmobile Group , GAFE . ( " Grupo Aeromóvil de Fuerzas Especiales " ) . The design was coordinated by the " Centro de Investigación Aplicada y Desarrollo Tecnológico de la Industria Militar " or CIADTIM ( Center of Applied Research and Technology Development Military Industry ) and SDN and all of its parts are built in Mexico . It is currently in use by the Mexican Army . Development . The development of the FX - 05 began as a 16 - month research back in 2005 with CIADTIM as part of research efforts to replace the HK G3A3 rifles that were in service with the Mexican military . Originally the HK G36 was supposed to become the Mexican military ' s standard rifle as plans were already drawn to transfer technology and equipment to Mexico to initially build 30 , 000 rifles at a cost of € 63 , 016 , 125 as part of Mexico ' s military modernization program . The Mexican government ultimately decided that they wanted a more cost effective alternative to the G36 , which resulted in the decision to end the project before any technology or equipment could be transferred and the FX - 05 project was undertaken . A Mexican report states that up to December 2006 , $ 84 , 000 , 000 Mexican Pesos ( € 5 , 855 , 698 at the December 2006 exchange rate ) were invested in the FX - 05 project , including raw materials and using only national equipment and technology . Leading the FX - 05 project was General Alfredo Oropeza Garnica with Brigadier General Jose Antonio Landeros . Design details . The design of the weapon includes telescopic , red - dot and mechanical sights ; cold - forged barrel ; folding and adjustable butt stock ; as well as the capability to semi - automatic , three round burst and full auto fire . It has a cyclic rate of fire of 750 rounds per minute . Most of the rifle ' s receiver is constructed of a polymer reinforced with carbon - fibers with an underlying titanium frame and comes in black , dark - green and desert - tan colors as well as the SEDENA digital camouflage patterns used by the Mexican army . The charging handle can be installed on either side of the rifle with gas piston located above the barrel , which operates under a multi - lugged rotary barrel system . Safety / fire mode selectors are located above the pistol grip on both sides of the FX - 05 . The internal mechanism and barrel are made of advanced corrosion - resistant stainless steel . An Indigenous programmable air - burst grenade launcher is currently under development for the FX - 05 , which will be able to fire standard NATO munitions in addition to Mexico ' s new RSE - 7 fuel - air grenade round . But until it is finalized the FX - 05 will use the AG36 grenade launcher as used on the G36 . The FX - 05 is one of the world ' s few assault rifles featuring polygonal rifling , which eliminates the normal grooves of a weapons barrel replacing them with a system of " hills and valleys " in a rounded polygonal pattern . The optical sight is an integrated one with a carry handle attached as standard . The FX - 05 is available in several configurations optimized for differing use , including ; Assault rifle , Carbine and Short Carbine . A light machine gun and sharpshooter version is also being made available . Legal status . On February 1 , 2007 , representatives of the SEDENA ( Secretaría de la Defensa Nacional ) and Heckler & Koch met in Mexico City to address accusations of patent infringement from the German firm . They claimed that the Army " replicated " the design of the HK G36 assault rifle . After an exhibition of detailed models of the FX - 05 , the HK representatives were convinced that , despite the similarities between the two rifles , there wasn ' t a patent infringement , therefore bringing an end to the disagreement . In the end , the German firm stated that they would not sue on the basis that even though the rifle looks similar it is internally different with a completely different mechanism . The report concluded that while externally the FX - 05 bears obvious design elements there are several notable differences . The receiver which was styled after the G36 is in fact coupled with a simple gas piston similar in operation to the AK series which is then attached through a delayed roller system to the weapons recoil delaying system . While the more advanced parts of the rifle were found to be independently Mexican produced , Heckler & Koch officials still questioned the DGIM ( the manufacturer of the FX - 05 ) regarding the issue of the rifles receiver system which is almost identical to the G36 ' s . It is believed that the receiver was made to be as similar to the G36 to maximize commonality between the two weapons as many of Mexico ' s police forces are issued with the G36 . Either way it appears that the newer post lawsuit versions of the FX - 05 feature a different newly designed receiver , as the newer FX - 05 come with a four position fire selection ( safe , single shot , three round burst , full auto ) whereas the original FX - 05 came with only three firing selections ( safe , single shot , full auto ) . This theory is also reinforced by the fact the new black FX - 05 models feature a visible metal protrusion before the magazine ejector and the receiver is noticeably smaller . The influence of the G36 receiver , AK styled gas piston and Mexican recoil delaying system can all be seen in the rifles partial cut away image .