F.M.C ‘S.F’ (Fabrica Militar de Cartuchos San Francisco)
The San Francisco Military Factory, was located in the province of Cordoba, Argentina and produced a variety of ammunition, although the initial main production was that of 9 x19mm Parabellum. Upon closure, manufacturing was transferred to the current FLB (Santa Fe) plant.
This is a match cartridge designated "Especial Concurso SS" and was made in 1976 by Fábrica Militar "San Francisco" of San Francisco city, San Justo department, Córdoba province, Argentina. The brown color was a post-1971 code for match ammunition (previously used for proof) and replaced the previous identification code represented by a small dot in the neck. This is the last year it was made and the only one in this caliber using the new code.
http://www.cartridgecollector.net/765-x-54-mauserSo basically you have a bunch of 1970's match grade ammo. Probably would still go bang, Others can chime in with more info.