[Diggit]

I am pretty sure they are 7.92×57mm Mauser.
And I found them them in former Yugoslavia if that helps.

Image in link
https://ibb.co/iHmiLT

[x]

Left: is mande by FN Belgium for Serbia, here just with Cyrillic font.
Right: "JR" is Georg Roth Pressburg (Austria) then in Czechoslovakia (city renamed to Bratislava) where his name was spelled "Jiri Roth" and the logo also changed from initially "GR" to "JR".

[x]

Both made in 1926.

[Diggit]

Thank you so much!

So would you say they were mostly likely used by axis forces?

[x]

As they are Serbian and we can not tell if they were fired before 1940 or later or again after 1945 it is impossible to tell.

[Diggit]

They were found around a series of bunkers which were held by the German army up april or may 1945 at which point the bunkers were conquerd by Yusgoslav partisans.
So I think it is very likely they were fired in 1945.

[x]

Yes, as for the context this makes sense.