The M1908 Mondragon is widely acknowledged to have been the first self-loading rifle adopted as a standard infantry arm by a national military force. There are a couple earlier designs used by military forces, but the Mondragon was the first really mass-produced example and deserves its place in firearms history. Designed by Mexican general Manuel Mondragon (who has a number of other arms development successes under his belt by this time), the rifles were manufactured by SIG in Switzerland. They are very high quality guns, if a bit clunky in their handling.
The design used a long-action gas piston and a rotating bolt to lock. Interestingly, the bolt had two full sets of locking lugs; one at the front and one at the rear as well as two set of cams for the operating rod and bolt handle to rotate the bolt with. The standard rifle used a 10-round internal magazine fed by stripper clips, but they were also adapted for larger detachable magazines and drums.
Unfortunately, the rifle required relatively high-quality ammunition to function reliably, and Mexico’s domestic production was not up to par. This led to the rifles having many problems in Mexican service, and Mexico refused to pay for them after the first thousand of their 4,000-unit order arrived. The remaining guns were kept by SIG, and ultimately sold to German for use as aircraft observer weapons.
For more information and photos of Mondragons, check the 1908 Mondragon page in the Vault.