7.63mm.
I don't have a 8.15mm yet (rare). If it's 8.15mm, I win lottery
A few were sold in auction in the past, but out of my reach. Just need to wait someone selling their 8.15mm as a 7.63mm. Not easy to find such a seller, but who knows...
But 7.63mm is OK too. I am fancy on 7.63mm caliber. It has very flat trajectory and excellent penetration.