With an optic to replace the AK's terrible iron sights, this shooter engages targets out to 425 yards; his ammunition needs to be accurate enough to get the job done.
Unlike virtually all other "7.62" or .30 caliber cartridges, the Russian 7.62x39 uses a non-standard bullet diameter: .310 inch instead of .30. Thus most "Western" .30 caliber or .308 bullets will not work in the 7.62x39. This is slowly changing as a a few bullet makers have come forth with modern bullets specifically for the 7.62x39.
The most interesting is the 123-grain Barnes TSX-BT. Barnes' TSX bullets are made from solid copper; they do not have a conventional jacket and core. The TSX bullet has a solid shank, and then a hollow-point nose. When the bullet impacts tissue, the hollow point expands to create a wide wound channel while the solid bottom shank stays solid for excellent penetration. The TSX-BT bullet has a boat-tail to incrementally aid the BC value. Barnes TSX bullets have yielded impressive results on game from .22 caliber up to .33 caliber.
Standard lead-tipped hunting bullets such as the Hornady 123-grain SP will produce predictable results on game. Lapua has a 123-grain FMJ bullet that ought to produce terminal results about the same as the mil-spec FMJ. Standard construction hollow-point bullets will produce more violent expansion and fragmentation, usually at the expense of overall penetration. Cor-Bon's 125-gr JHP and the Wolf "Military Classic" JHP both will provide increased terminal performance over standard FMJ. The Wolf JHP shows fragmentation in ballistic gelatin.
Regular .30 caliber bullets are not proper for 7.62x39; Barnes, Hornady, and Lapua are three manufacturers with bullets specifically for the Russian cartridge.
The second untapped strength of 7.62x39 is the use of heavier bullets. Although the vast majority of loads use a 120 to 125-grain bullet, a 150-grain bullet - the mainstay of .308 Winchester loads - can be fired at 2100 to 2200 fps from a 16-inch barrel. Going further, a 175 to 180-grain bullet can be fired at 1900 to 2000 fps. As bullet mass is increased, the ability for impressive penetration and terminal effects improves. These heavy bullets will lose even less velocity as barrel length is reduced. For example, a 180 grain load may lose only 100 fps as the barrel length is reduced from 16 to 12 inches.