The big problem isn't reduced velocity at 300 yards. Instead it's assuming the rifle will retain the same point of impact at ONE HUNDRED YARDS in really cold weather.
I have tested a bunch of rifles and loads at zero after sighting-in at "normal" temperatures, and they will shift POI significantly at 100--and there's no way to predict how it will change unless you try it.
This reminds me of the angst that is sometimes expended on the virtues, even the "virtual need", for controlled round feed rifles and then negating whatever reliability you gain from that by making ammo which may not chamber easily 100% of the time, or throwing some other problem at it.
I know various fillers, strengtheners, and stabilizers are added to synthetic stocks in the form of glass, carbon, and/or kevlar fibers, but synthetics... plastics, are notorious for expansion variances, often much greater than wood, with temperature changes.
