The 1:8 is designed for the heavier bullets. Not sure if this is good for 75gr but certainly good for 69gr bullets. I have shot from 40gr to 69gr in mine and they all worked. Fast twist is more likely to destroy the lighter bullets due to the twist rate than to not stabilize the heavier bullets. I ended up using 55gr in my T3 just because I wanted a balance of speed and reasonable weight bullets.