The marking at the lower right of the label basically says “Loaded in April 1938.” I thnk that is self-explanatory.
The box is from the Consorcio de Industrias Militares, Artelleria - Pirotecnia Militar de Sevilla. My box, identical to the one shown, contained mostly cartridges with the headstamp C I M PS (“C” at 12 o’clock, “I” at 9 o’clock, “M” at 3 o’clock and “PS” at 6 o’clock). One of the cartridges had no headstamp, but the same characteristics. I think the lack of a headstamp in this instance was purposeful, and the cartridge may not be original to that box, although it is definitely Spanish. I have a full clip of these same, unheadstamp cartridges; the clip is from Pirotecnia Sevilla.
The cartridges are brass case, brass primer cup, and CN (non-magnetic) FMJ RN bullet.
The box held two ten-shot stripper clips (the depth of the box will accommodate them), but they were missing from the box when I obtained it. Only about 6 or 7 rounds were left. The clips were likely marked “PS” enclosed in an oval, not to be confused with those stamped “P.S.”, with serif letters and periods after the letters, inside a much more elongated oval than that on the Spanish clips, and which are from Patronenfabrik Solothurn, Switzerland.
Below is a second box of similar, but not identical, label to the one shown by Lew. It originally contained two 10-shot clips with cartridges marked C I M PS, but in this instance, a change, for whatever reason unknown to me, in the order of the letters on the headstamp, in this case with the “C” at the 9 o’clock position and the “I” at the 12 o’clock position on the head. I have samples of both cartridge headstamps in my collection. The clip was as described above, marked “PS” in an oval.
Edited heavily to add and correct information due to finding a second box, as well as cartridges with no headstamp, and both forms of “CIM” headstamped cartridges, in my collection, research I should have done before I started on this. Sorry about that.