Information about the Sociedade Nacional de Cartuchos e Munições Ltd. is hard to come by but I can tell you that this company existed as such in 1927. During that year company name changed to Sociedade Anonyma Fabrica Nacional de Cartuchos e Munições. In 1929 name changed again to Fabrica Nacional de Cartuchos e Munições S.A..
According to CBC literature (later copied elsewhere) its predecesor was named Fabrica Nacional de Cartuchos e Munições (FNCM) and established in 1926 but evidence shows that the original name was SNCM.
During the 1930’s FNCM used both “FNCM” and “SNCM” as ammunition trademarks. In november 1936 these trademarks were transferred to CBC.