The only light I can shed on this subject is comparing loading manual velocities from 24" test barrels to real life velocity from my 26" 300 win mag.
Most of the books show 180gr bullets with 70grs of H4831 between 2700fps or so up to close to 2800fps with 24's. I have chronographed this particular loads many times out of my 26" barrel and gotten a very consistent 2875fps. The chamber on my rifle is supposed to be a minimum SAAMI hunting chamber.
Take it for what it is worth.
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