>>64119977
You want 2k fps (at least) to be your impact velocity not your muzzle velocity, you want the cavity generated by the bullet to expand fast enough that it exceeds the elasticity of the flesh it's displacing so the cavity becomes permanent, that's what makes rifle wounds different to pistol wounds. The exact velocity this occurs at goes up or down inversely with caliber, with 7.62 it might be higher than the commonly cited 2k figure sourced from this paper: emergencymedicinekenya.org/wp-content/uploads/2015/09/1211-Ballistics.pdf
Were I shopping for a 7.62 AK I wouldn't go any shorter than the 104, the cartridge struggles enough at range as-is. You must have seen picrel before, allegedly this was a 7.62 hitting at 150 meters.