Twist Rate

[StoneHendge]

I would take a look at what bullets you expect to be shooting and what velocities you expect out of whatever length barrel you choose and run them through the Berger Twist calculator at your coolest expected temperatures. If it works at 7.5, I'd go that route. No one ever talks about it and there probably has been no real research done outside of the military (who isn't going to share results), but faster twist has it's downsides with potential jacket deformation and even slippage in the barrel. Even the type of rifling and amount of grooves can come into play with the amount of centrifugal force on the jacket near the end of the barrel. As the envelope keeps getting pushed with higher and higher bc bullets, I think it gets into a damned if you do damned if you don't scenario (see 224. Valkyrie). The Proof's are 7.5 and they were the barrels used to develop the cartridge with the military. If any one has the money to test the effect of twist rate on dispersion at long range and recover fired bullets to examine them for deformation, it's your tax dollars!

I'll add that I don't think I've ever seen a 7 twist 6 Creedmoor.