7.62x39 vs THE TOUGH ANIMALS?

how would this caliber stack up against big animals like small elk,large elk,moose,grizzly,and the bison, ALL within 50 yards so it could keep its energy, which in this case has 1762 ft/lbs traveling at 2350 fps,ONLY WITH HEAD SHOTS WITH THE BISON AND GRIZZLY, IM ASKING THIS BECAUSE I SAW A VIDEO ON YOUTUBE OF SOMEONE SHOOTING ONE A BISON IN THE HEAD WITH A 6.5 GRENDEL WITHIN 75 YARDS,i dont know exact yardge.but i know enough to say that the 7.62x39 and 6.5 grendel are ballisticlly similar with 150 yards,after that the 6.5 flies straight while thr 7.62 drops with rainbow trajectory.THANKS