I am not dissing the 300 Win Mag. But the 6mm is lighter, has better accuracy, less recoil, but less downrange energy though adequate. All the low light is optics, not gun. The 6mm is easier to get hits under any conditions so that is what I would pick. But, I was not on the selection committee so my opinion does not matter. The 300 Win Mag is better for the application than the .308/7.62X51 so that is still a good move. A 243 Win has hardly more recoil than a .223, but has great long range capability so I just think it would have been a good choice and is why it is so often chosen by long range target shooters. If I had to get shot, I would not pick to be shot by a 300 Win Mag.
I understand your point...
I was fortunate enough to work a program with a 6.5mm projectile on a cartridge case that had about the same volume of a 338 Norma Mag...1/3 the recoil of the .300WM, same KE on target at 1000M as the AB43. Talk about a flat shooting hot rod...lol