This is an oddly specific question!

The armament of Chile during the First World War was a consequence of a decision in the aftermath of the War of the Pacific (1879-1884). While the conflict resulted in a complete victory by Chile over its Peruvian and Bolivian foes, it exposed many weaknesses in organization, strategy, and tactics that had during that period of time been dominated by a French influence. As a rising geopolitical power, Chile turned to the German Empire for help to modernize the Chilean army. Subsequently, the Chilean army received a complete overhaul not only in organization and tactics, but also in uniforms and armament. Unsurprisingly, the German-made Mauser M/95, made by Ludwig Loewe & Company in Berlin, came to be the primary small-arm in the Chilean army from 1898 until ultimately phased out by 1985 (by which time it was mostly used as a ceremonial rifle, something which it is still used as today).

Consequently, by the time we reach 1973 and the Pinochet regime, what had once been a Prussian-style army had after the Second World War become heavily armed with American and other Western firearms. The allegiance of Chile with the allies (particularly the United States) during the Second World War and subsequent military treaties with the United States resulted in an influx of American weaponry and uniforms into the hands and bodies of Chilean soldiers. The M1 Garand was therefore the primary rifle for Chilean soldiers into the 1960s, and they can still be spotted in the hands of Chilean soldiers in photographs of the 1973 coup d'etat. Yet the most commonly equipped rifle during the Pinochet regime was the Swiss SIG SG 510-4. Despite this, the FN FAL and G3 rifles were used by Chilean soldiers during the Pinochet years, although not in the same quantities. The majority of the armaments that Chile acquired in the 1970s was unsurprisingly supplied by the United States, in particularly during the long years of tension that Chile had with Peru at their northern border (and with the Soviet Union supplying Peru during the same period).

For more information, see The Grand Illusion: The Prussianization of the Chilean Army by William F. Sater and Holger H. Herwig (University of Nebraska Press, 1999) and Chile and the United States: Empires in Conflict by William F. Sater (University of Georgia Press, 1990).

As for sources about the Pinochet regime, this is a huge question because the bibliography about the dictatorship has since the 1990s practically overshadowed all other subjects related to Chilean history. Is there anything more specific that you're after? If you're looking scholarship into the Chilean soldier during this time period, you should definitely read The Wars inside Chile's Barracks: Remembering Military Service under Pinochet by Leith Passmore that explores the social and cultural history of this period.