Dutch - yes, we did make 7.9 x 57 ammunition during WWII. Remington made some for sure, but I have never been able to pin down the headstamp they used. I have two different blanks and a dummy with the headstamp “REM-UMC 7.92M/M” which would be the likely headstamp. However, I don’t have a ball round with this headstamp. I do have a FMJ spitzer bullet round with the REM-UMC 8M/M designation, and a brass primer with purple seal. It certainly was for some military contract, and probably during the war. Woodin Lab has some tracers produced by Remington, as well, but don’t recall the headstamp.
There is also a headstamp “WRA 7.92” that is probably from WWII.
The only ones I can certainly identify as being from WWII were made by Western for China, and most of these rounds are dated, and have two Chinese Ideographs, one at the 9 O’Clock Position and one at the 3 O’Clock position. They are enocuntered with no date at the 6 O’Cock position, in which case the two Chinese ideographs are the entire headstamp, or with the dates 42, 43, or 44. I have, counting Chinese repacked ammo, sealed in China at the neck with a green seal and at the primer with a red seal covering the entire primer, 11 different ball rounds and 4 different dummies. They are found with GM and also with GMCS FMJ Spitzer bullets. The boxes for this ammo were also printed in Chinese. The basic headstamp with date is pictured in “Cartridge Headstamp Guide,” by white and Munhall, as number 367 on page 48.
Now, I said those were the only ones I could positively identify from WWII - it is absolutely a certainty that ammunition in this caliber other than the chinese-contract noted was made during WWII for various lend-lease countries. They are probably with the Remington and Winchester headstamps noted, but regardless, ammo was made. The problem is, I have other U.S. 7.9 with military-type FMJ Spitzer bullets, including one that probably dates from WWI, since it has a copper primer with impressed “U” on it.