.300 win mag rifle isn't much different than a standard hunting shooting .308 or 30.06. Sniper heavy barrels will add weight over a hunting barrel but it's still under 10 lbs. A .50 runs upwards of 30lbs making it not very portable.
There’s a big difference between .300 and 7.62 nato imo. The ammo they’re using is a 220 grain boattail hollow point leaving the muzzle at about 2,850 fps. That’s potent. M118 special ball uses a 175 grain projectile and leaves the barrel at 2,600 fps. The increased weight and velocity will significantly decrease wind deflection and extend the range well beyond what is normally seen with 7.62 special ball. Looks like the .300 projectile has a .618 Ballistic Coefficient versus the M118 rounds .502 BC. .618 is a big improvement IMO. I think this is a a good move. The .300 WM will shoot better than most snipers.