What is the story about these rounds? The 2000 dated examples are 7.62 x 37 and are so headstamped (has both RG and HK headstamp markings). The bullets differ only in the moly(?) coating. The 7.62 x 34 loading has a ‘R-P 221 Fireball’ headstamp. By x-ray, they appear to be loaded with similar projectiles. I’m assuming that the ammo is of British manufacture and the weapon is by HK - i.e. a joint venture that has since come to pass.
In the following picture is a ‘standard’ 7.62 x 37 with other loadings based on the .221 Fireball case. Are these rounds related? What other variations are out there that I have to be on the look out for?