It more depends on the chamber and throat than the twist, that said 1:9's don't really work with long bullets.
If you are looking for an accurate paper loading the 69gr SMK stuff is good -- your best of handloading as most of the .223 ammo was designed around a bolt gun and is not crimped well for use in a semi-auto.
1:7 is the best twist for most bullets in 5.56mm, 1:8 is also a good twist.
-Kev