Is there any science to what twist rate is correct or is the best you can do is make an educated guess? I currently shoot a lot of 338 cal and a 1in 12 works great for 250s. I know in most calibers a 12 twist is way too slow. I am getting ready to build a gun in .243 cal and it looks like most guns in this caliber are either 8 or 9 twist. Does the required twist rate get faster when you go down in bullet diameter? I do not plan shooting over 80 or 90 grain bullets in this gun.