About the only military ammo I have run across which LACKS COMPLETELY a headstamp, is Japanese. Anything else is generally well-marked, but you have to be able to read the markings..... and often you will find far more information on the BOX than on an individual round.
RIFLES are a different matter, however, and what WE call the thing might be one thing but what the ARMY called it might be something else. A good case in point is the Model 1898 Mauser as used in German military service for so many years. The rifle was governed by the SPECIFICATION laid down at the time of its adoption. The early "long rifles" were marked as "Gewehr 98" (Rifle 98) even though they all used the action developed by Mauser in 1897. Once the testing phase was concluded, the Army wanted the new rifle but they also wanted it to be MODERN, so it was called the 98 because that is when it actually went into production. For a rifle to be designated as a Model 98 AND have German military ownership markings, it HAD TO meet the SPECIFICATION laid down by the military FOR THE 98 RIFLE. In the case of the 98, that Specification included the bore diameter (7.9mm) and the chambering. Bore diameter (CALIBRE) was marked at the breech end of the Barrel where it could be seen; very often there will also be a tiny marking on the BOTTOM of the barrel to tell you what it actually GAUGES..... which often is not a PRECISE 7.9mm; it could be 7.89, 7.90. 7.91 or anything within the SPECIFICATION.
And yes, they would have marked it as "7,9" rather than "7.9", because that simply was their way of doing things: they use commas where we would use periods and periods where we would use commas.
Happy collecting!