I use it in my 280AI with a 1:8 twist, but it keyholed at 100 yards from my 280AI with a 10 twist. Could go either way with 1:9 depending on powder used and speed attained.Anyone running the 7mm 155 grain hammer hunter in a 9" twist? Putting together a 7mm mashburn and was curious if I could get by with a 9 twist. Bullet would be around 3250fps and 3000' of elevation or higher