My 243 isn't the ultra varmint but it has the 1-12 twist. I found that it would stabilize and shoot 65 grain through the 85 grain bullets in hand-loads and factory 100 grain loads by Federal well. The challenge was finding the right speed of powder with the hand-loads. IMR-4064 shot the 65 grain bullets good but was very temperamental, and it wouldn't shoot the heavier bullets and group very well. I went to IMR-4350 (slower powder) and shots grouped a lot better.
