7.62x39. There are a few good factory loads out there, but x39 really shines when handloading. It's like a different cartridge altogether. There are endless projectiles available because many .308 diameter bullets shoot as well or better than .310 to .311 offerings.
I load mostly .308 bullets, and those loads perform well in both my vintage Ruger 189 Series Mini-30 and my brand spankin' new CZ 527. I've had my CZ for just over a year. I've not shot it nearly enough.
The cartridge performs best with bullets between 110 and 150 gr. I have quite a selection of Speer .308 bullets, but also Hornady, Nosler, and Sierra. Two of the most popular bullets used by handloaders for deer hunting when the Ruger Mini-30 was first introduced in the late 1980s were the Sierra 135gr .308 spitzer single shot pistol bullet #7350 and the Nosler .308 125gr Ballistic Tip #30125. The Nosler 125gr is a screamer at over 2,500 fps and with a relatively high BC for the species it can really go the distance. Too many other projectiles to name.
My favorite powders for x39 are Accurate 1680, Accurate 2200, Hodgdon CFE BLK, and two Lovex powders; Shooters World Blackout and SBR-SOCOM.
Favorite primers are Winchester LR and CCI 250. I've got all kinds of new brass... mostly Lapua, Starline, Geko, and PPU. I was lucky to have stocked up on reloading components before the pandemic and election 2020. It was just dumb luck that I was in a phase of acquiring stuff. I still find ok deals here and there, but no new primers lately.
Well anyway 7.62x39 is a fun cartridge to handload. I get a lot of satisfaction from sending high BC 140gr projectiles at 2,450 fps while many domestic factory rounds are limping along below 2300 fps with 123gr bullets.