I don't know if you've messed with your #1 trigger before... they are a difficult to work on and a pain in the butt to get to. Then again, If you're getting that kind of accuracy out of it I wouldn't mess with it.
Depending on the age of your 6mm you may have a1 in 12 or a 1 in 10 twist barrel - most likely the 1 in 10 if you're stabilizing the 100 gr SBT. Try the 105 A-Max first, a lot of guys can still stabilize those in a 1 in 10.
If you're thinking of re barreling the 220 swift don't let the dies be a consideration since you can sell then on this site along with your brass. Also do rule out the 115 DTACS from David Tubb for an all out long range rifle... DavidTubb.com.html