I noticed nobody is talking about RPM with respect to twist rate. When you shoot frangible bullets at high speed along with too fast of a spin, they have a tendency to blow up. I select twist rate based on the speed I am getting with the load, and then calculate RPM to be at or below the bullet's limit.
Here is some manufacturer's data on what they suggest maximum RPM should be with their respective bullets:
Dogtown 260,000
Varmint nightmare 260,000
Speer TNT 240,000
Hornady VMAX 290,000
Hornady SXSP 240,000
Sierra Varminter 216,000
Sierra Blitzking 352,000
Here's the formula to calculate RPM: (Muzzle Velocity * 720)/Twist Rate
So for instance a load going 3,350 fps in an 8 twist barrel is as follows: (3350*720)/8 2,412,000/8 = 301,500 RPM.
So using the chart above, I would be ok using the VMAX limit, as its pretty close to the 290k limit. You have to test though of course.
Lets say you are thinking about a 7 twist. Running the same numbers, that would be 344,571 RPM. Good chance of blowing up many of the bullets listed above with the exception of the Sierra Blitzking.
The advantage of high RPM is terminal effect on the target. More spin = more acrobatics and guts. So experiment with different numbers and pick the twist rate that gives you the highest RPM that the bullet will survive.
The new ELD VTs need a higher twist rate to stabilize, and I'm sure their spin limits are probably higher than anything listed on the chart above. If anyone knows this number, please post it.
Real world example: I had a couple of 8 twist 6 creedmoor barrels laying around. They were blowing up vmax's left and right. I then switched to the 80gr ELD VT and that solved the problem. I also found they are just as destructive as the vmax's based on the tests I did in this thread:
Hornady Varmint Bullet Shootout