Straight-pull bolt-action rifles
In 1891 Mondragón began working on a rifle design. During his stay in Belgium he filed a patent application for which he had received a grant on March 23, 1892 (No. 98,947). During the same year, on April 20, Mondragón received also a grant from the French Patent Office (No. 221,035). In the following year, on February 8, he also filed an application in the United States Patent Office (No. 461, 476) and received a grant (No. 557,079) on March 24, 1896. The rifle, referred to as M1893, was of a straight-pull bolt action design, chambered for 6.5x48mm cartridge (also developed by Mondragón), with a fixed magazine fed with 8-round en-bloc clips. The rifle had three settings: "A" - automatic, "L" - safe and "R" - rapid. The "automatic" fire setting allowed the rifle to fire a cartridge each time the bolt was manually cycled to closed position, in similar fashion to Winchester M1897 pump action shotgun. The rifle could be equipped with a knife bayonet. The bayonet measured 41 cm and weighed 575 g, the blade was 28 cm long. At the time Mexico had no manufacturers capable of producing such a complex design to the required tolerances, Mondragon with the backing of Diaz entrusted the Swiss Industrial Company (Schweizerische Industrie Gesellschaft) of Neuhausen, Switzerland with the production of the rifles. SIG received the first order in 1893, for 50 rifles, and another one in 1894, this time for 200 rifles. The rifles from the second order were chambered for 5.2x68mm round and referred to as M1894 (to differentiate them from the ones chambered for the 6.5mm cartridge). The 5.2mm cartridge was developed by Swiss colonel Eduard Rubin.
Mondragón continued his work, and on August 8, 1904 he filed a patent application (No. 219,989) for the new rifle, this time of a self-loading design. He received the patent grant (No. 853,715) on May 14, 1907.
The design was adopted by the Mexican Army in 1908 as Fusil Porfirio Diaz Sistema Mondragón Modelo 1908. The same year, the Mexican government contracted with SIG for the production of 4,000, M1908 rifles, chambered for the 7×57mm Mauser Mexican service cartridge. Due to the political instability of Mexico at that time (Mexican Revolution), by 1910 only 400 of the ordered rifles had been delivered by SIG. The rifle's inability to cope with ammunition of poor quality, and the high unit cost of 160 SFr per rifle, led to the cancellation of the order by the Mexican government.
Mondragón Modelo 1908 was a gas-operated rifle with a rotating bolt, and a cylinder and piston arrangement. This design is now common, but was unusual at the time. The bolt was locked by lugs in helical grooves in the receiver. There was a switch, located on the charging handle, which would disengage the bolt from the gas system, changing the firearm into a straight-pull, bolt action, rifle. The rifle had a non-detachable box magazine and was filled by two, five round, stripper clips. The Mondragón Modelo 1908 rifles were fitted with a bipod. In addition to the knife bayonet introduced with the previous rifles, Mondragón designed a spade bayonet for use with the Modelo 1908, for which he filed a patent application (No. 631,283) on June 6, 1911.