I had some hornady SPSX bullets that really baffled me for a while.
They are softer than the air they are parting at a certain velocity. I thought I was below this velocity, but wasnt.
I didnt realize it a first. All I knew is that I wasnt hitting paper at 100m all of a sudden. And then at 50, same thing. 25m, STILL nothing!
Then at a distance of about 5 paces, I got what can only be described as tiny shotgun pattern.
I think it was 2600fps was the threshold, but not certain.
So I guess I dont know anything about the rate of twist damaging a bullet to this point, but the hardness vs velocity is a factor.