Quoted: The 75gr bullets appears to be in the grey area. If you read the Ammo-Oracle you will conclude that 75 won't work but many people have no problems with them in 1-9 barrels. Bushmaster's website states the a 1-9 will stabilize a 75gr bullet. The only way to know is to try it in your rifle and see.
I personally feel that barrel length has something to do with it also, because as the velocity goes up so does the spin from a given twist rate. I would bet that more short 11.5" 1-9 barrels don't like 75's and most 20" 1-9's do fine.
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The Ammo Oracle is wrong if it states that 75 grain bullets will not work at all in 1/9 barrels.
I know for a fact that the Hornady 75 AMAX, a bullet significantly longer than the Hornady 75 HPBT, is perfectly stabilized in a Winchester Model 70 with a 26" 1/9 barrel.
So 75 grain bullets definitely stabilize in barrels longer than 20" (I know because I know people who started in HP with a 20" 1/9 AR and 75 gr Hornadys). But might not stabilize in shorter 1/9 barrels due to the shorter time the bullet spends rotating in the rifling (lower rotational acceleration = lower rotational velocity).