Sometimes its tough to tell when you are holding a cartridge if it is copper or brass cupped. Unfortunately, brass primers, when they tarnish under certain conditions, turn copper color.
There is nothing other than the slight copper shade of the primer cup that DOESN’T say “Tokarev” on this cartridge, however. Again, I will stick to my evaluation that it is 90% sure a Tokarev cartridge, not Mauser, Borchardt or Mannlicher. Almost academic, as those four rounds are a lot more similar than most people think. DWM, for example, did not differentiate between Borchardt and Mauser, with boxes labeled for either cartridge bearing the numbers 403 or 403a (essentially the same number - you can find either on Mauser boxes, some quite contemporary. I have two identical DWM boxes for twenty rounds of Mauser on strippers, and one has the “403” and one has the “403a” number. Again, otherwise, the boxes are identical.
The loading from DWM for Mauser and Borchardt were evidently the same, when one examines all the entries in their literature.
Most of the size differences in the various cases all fall within + or - tolerances for the 7.63 Mauser.
The GMCS bullet, lack of headstamp, three-stab bullet crimp - all point to a common Tokarev cartridge. I could be wrong, but I don’t think so. Again, I have never seen an unheadstamped, confirmed .30 Mauser round with GMCS bullet. Perhaps a measurement of the primer diameter would help. I don’t recall off hand if the Russian primer is a different size than most primer cups for the 7.63 Mauser or not. It is certain that the cartridge is neither Borchardt or Mannlicher, in my opinion. Nothing much fits, except external measurements, for either of those rounds. I am talking about features.