I killed a few axis deer ( a big buck still in velvet for a pedestal mount) and a Scimitar Horned Oryx ( 41 1/2 bull) with a little 6mm/222 Magnum ( 6x47) with an 85gr xbt. I had a long barrel ( 27") and got 2900fps with a pinch of BLC2, 243Win speed. But you had to shoot it right! The headstamp didn't match up either. Only reason I had it was I was recovering from a neck surgery ( miserable few months) and had a chance to go shoot some Exotics. I had already been there and used a 220 Swift/55gr TB and the Rancher wanted it. So I traded him the Swift and some money for the oryx. I had a brake on the Swfit (too see where my bullets hit on varmints) but the 6x47 didn't have one. I later had that rifle converted/rechambered to a 243 and took it to South Africa. I left it with my Afrikaan friend. He liked the long barrel.
I killed game with a 6mm/284 and 6.5/284, no headstamp match either. BUT, when I went though Customs in South Africa and Namibia, the rifle/Headstamp very much mattered, ha. Although my 35 Whelen Imp slipped by!