Re: 208 AMAX, 1:12 twist FPS?
1:12 twist may not be sufficient to stabilize the 208grain bullet. Berger recommends 1:10 for their 210VLD but I have seem them stabilize in a 1:11.
In terms of velocity from a 20" barrel (assuming you could stabilize the bullet), I would think you might be able to get 2400fps.
I'm not gonna shoot here. I'm gonna shoot waaaaaaaay over there!