Complex sentence: The initial designs were straight-pull bolt action rifles (M1893 and M1894), those rifles served as a basis for developing Mexico's first self-loading rifle, the M1908, which was also one of the first such designs to see combat use.
Split into simpler sentences: The initial designs were straight-pull bolt action rifles (M1893 and M1894), those rifles served as the basis for developing Mexico's first self-loading rifle (M1908). The M1908 was one of the first such designs to see combat use.