Readers of this forum are aware that mentioning “7.92” may likely trigger a message from me. :-) Well, here it is.
The book “Nederlandse vuurwapens 1895-1940” by de Vries and Martens calls the Dutch machine gun cartridge caliber (p. 145, 158, 274 for example) “7.9” as in Germany. Its not 7.92 which (I believe) is of Czechoslovak origin. The cartridge is described as 7.9 x 57R in the book.
Dutch military ammunition types were identified by a number. Box labels did not mention the caliber. Therefore, the 6.5 mm rifle cartridge was simply marked as “Scherpe No. 1” and the 7.9 mm as “Scherpe No. 23”. “Scherpe” indicates live (Blanks were “Losse”). British .303 was Scherpe No. 17. So, never a caliber on the labels.
According to the book, the 4x90 headstamp has the meaning:
12 o’clock: case production year (aanmaak), for example 30
3 o’clock: cartridge loading year (samenstelling), for example 31
6 o’clock: letters for brass producer (possibly with lot number), for example O
9 o’clock: propellant lot number, for example 16
Dutch boxes show the headstamp of the cases also on the label.