With swift velocities, I would disagree with Fiftydriver's recommendation of a 12 twist. /ubbthreads/images/graemlins/shocked.gif
Think about it. Most 222 rems, 22 hornets, 221 fireballs, and 22-250s all have 14 twists from the factory. This is because they know that most people will want to shoot 40 grain to 55 grain bullets. The average lengths of these bullets is not very long (thus not being hard to stabilize) and they work in a 14 twist clear down to 3000 fps. So a swift at velocities approaching 4000 to 4300 would even need less of a twist to make these particular bullets work and in fact, the lower rpm's induced to those bullets by say a 16 twist would actually help to settle them down more quickly right out of the barrel. That could in theory translate to better 100 yard groups. I am not saying a 14 twist won't shoot great groups at 100 (mine in fact shot 1/4" groups at 100 quite regularly) but it is something to tinker with.
A 12 twist would be good for the 60-70 grain range indeed. However, if you are going to get a whole new barrel with a different twist, I would go with an 8. This will put you into a whole new league as far as what bullets you can shoot. The 80 grain VLD style bullets have <font color="blue"> DOUBLE </font> the bc of the 55's and can effectively increase your range to around 1200 yards from about 800 with the 55's.
Just something to think about! /ubbthreads/images/graemlins/wink.gif