Bullets shot from a faster twist barrel at a higher muzzle velocity retain most of their spin rate, even when velocity has dropped off. This helps them expand at, say, 1800 fps, when bullets shot from a slower twist at a lower muzzle velocity might not expand at all at 1800.
I don't want to hijack this thread but could you please elaborate a bit why a faster twist rate would produce more expansion? I get the whole faster velocity thing but the twist rate is new to me. A 1:8 twist vs 1:16 twist on paper is twice as fast but we are still only talking 1 complete turn in 8 or 16 inches - more than the average thickness of a ribcage on most broadside animals.
