I have a similarly marked Box, of SMK ( no trace etc.) and it is Full of “E37 RWS” headstamped SmK (Red primer seal).
There being No indication of the maker on the Box, could the lot have been made by one of the RWS Plants, and shipped to Portugal in 1937 --the year Portugal (a) Adopted 7,9mm as their standard Calibre (b) Bought their first lot of Modified Mauser Kar98k rifles (M937 § from Mauser; © began conversion of the AE ammo plant to make 7,9mm ammunition by acquisition of new case making machinery ( on the German primer design – two hole Berdan) and (d) saw the ascent of Salazar as the Dictator of Portugal ( and a friend of Adolf Hitler, both Politically and personally)…but savvy enough, like Franco in Spain, to maintain neutrality during WW II.
Would these “Special tracer AP” etc. be also “E37 RWS” marked ???" ( Export 1937??).
BTW, the Metralhadora mentioned are the following (not all inclusive): M13,( Bergmann); Madsen M937 LMG, M30 Solothurn, 7,9 Aircraft Browning (FN), Converted Vickers (from .303) and Breda M937 ( during WW II)… I don’t know if any of the WW I Lewis guns were cvonverted from .303, or just replaced by the Madsens?? I also think that there were somne Early Hotchkiss Guns also converted to 7,9 as well???( orig. 6,5x58 or .303??).