I was wondering the same! Sierra states 1:10 or faster but wonder if you pushed them fast enough in a 1:12 if they'd stabilize. Hard to beat the .323 G1 BC of them!
I shoot a different 60 grain bullet hornady #2275 now discontinued in a Remington 700 with a 1-14 twist and it shoots very well.
maybe just lucky though.
I luckily stumbled across one box of 60 tmk's at my local guns shop on saturday, im planning on loading them up with some imr4064 and hope to find something fast and accurate