Barrel bore and bullet diameters are all over the place for the 7.62x39 mm (Russian) with the former measuring from 0.308" to 0.311" and the latter being 0.308", 0.310", 0.311" or 0.312".
Caliber 7.62 x 39 (M43) Russian
Feed Your AK: Great AK Ammo Options - Gun Digest
Handloads: 7.62x39 mm (Russian)
7.62x39mm Gel Test - 7 Loads Put to the Test - Firearms News
Complete Reloading Manual For The 7.62x39 PDF
Handloads: .25-35 Winchester An Official Journal Of The NRA
The Complete Reloading Manual for the 7.62 x 39mm: unknown author: : Books
Handloads: 7.62x39 mm (Russian)
Handloads: 20 Gauge An Official Journal Of The NRA
Russia's Greatest Round: 7.62x39 - Guns and Ammo
7.62×39mm - Wikipedia
GUNS Magazine Reloading the 7.62x39 - GUNS Magazine
Modern Intermediate Calibers 002: The Soviet 7.62x39mm -The Firearm Blog
Can you reload a 7.62x39 bullet into a 7.62x54r case to increase velocity at the expense of mass? - Quora