In my opinion, one shared by many, these are clandestine headstamps. The codes are not “German Codes.” That is, they were not codes assigned to ammunition makers during WWII. Some make something of the fact that these codes are in the original German code book. Well, of course they are - all letters and letter groups from “a” thru “ozz” are in the code books that have been found so far.
I do not believe that the date “44” represents 1944. I do not know if it represents any real date, however, one way or another. Most “oma” rounds don’t have a date. An “oma 44” is known, but is very rare. I believe it is known from only a single specimen.
The first of these headstamps I encountered came in a huge shipment of mixed ammunition from Israel. They were definitely made in Czechoslovakia, who at first, before the heavy Russian influence took over, had very good relationships with Israel and in the late 1940s and early 1950s, supplied them with a great deal of military materiel assistance.
There are other codes found on 7.9 x 57 Mauser - “ux” and “usa.” There were also unheadstamped Czech 7.9 x 57 rounds made and sent to Isreal, and perhaps 9 mm as well.
To date, I have never heard anyone attempt to make an identification of the factory making these rounds. It is pretty obvious that if Czech, as many think and I firmly believe, that at least one of the codes actually represents Sellier and Bellot. Which one, and whether the other represents Povazske Strojarne or not, is unknown to me.
These rounds are often found with no seals, black primer seals, or red primer seals with red case mouth seals as well. I have no theory as to why this is.