From sources I can find, the difference lies entierly with the usage of the lighter Type L bullet, or the heavier Type D bullet.
Soviets were rather unique, and decided to adopt two interchangeable, but unique standard cartridge designs. One was the 1908 Type L, lighter with greater velocity, it was the most common cartridge during WW2 for infantry use, as it was intended for rifles and LMGs. Tthe 1930 Type D was a heavier bullet, intended for long-range stable shooting and MG usage. The “gr” or “grains” measurement is not about the propellent charge, but about bullet weight.
The Type L is closer in performance to the US .30-60, whilst the Type D is closer in performance to .303 British or 8mm Mauser.
All of this is to say, though, that current body armour eliminating OHKs at point blank ranges is utterly ridiculous, as we’re talking about 150m before it’s effective at stopping penetrations (which is not the same as it not hurting like hell, but that’s another matter).
Who here are engaging in firefights at this distance in game…? Come on, call up your names.
Not only that, as soon as we bring up .30-60 or 6.5 Arisaka, the body armour should just fold, as their greater velocity gives them greater penitrative ability should drag the ranges out to 200m or 250m range as the test would suggest. That’s not the case in game currently (granted, the US does not currently face the Soviets outside of custom battles, but it’s yet more proof that the flat 10% reduction, at all ranges, is unrealistic, and no testing will approve of its existance. They do however face Japan, who should be ignoring the body armour at even greater ranges).
With the other considerations (the bonus being applied on areas not covered by the plate, and protecting against fire as well), the current implementation of body armour is 100% unrealistic.