This is misleading. The 7.62x39 was not designed to kill 150-200lb ANIMALS. It was designed for warfare against human beings & most importantly, to operate in both full & semi automatic rates of fire weapons. Those were the parameters of the 314 cartridge designs looked at by the Soviet Armament Commission at the time, of which only 8 were manufactured & of course the x39 won the bid for production in 1943.
Oh! And if the argument is 150-200lb Humans being the equivalent representation of Animals, again.. no. Human beings & Game animals react far differently to gunshots. While dying is immanent in both cases, yes.. the goal in hunting is to bring about death in the quickest time possible. Where as with small arms in warfare during WW2, and ESPECIALLY by those like the Germany & the Soviet Union, quick death was not the primary goal. Stopping soldiers by wounding or rather horribly wounding in the aforementioned country’s case, was the intended design.