I've settled on Berger 150s for mine with it's second barrel. With the first barrel they were right next to dusting at AM velocity.
I'm waiting for the Berger 170 offerings but am getting a little long in the tooth to wait much longer.
By now Kirby may have some different/better ideas on rifling. All the 270 AMs that I know of are 3 groove 6 twist Liljas. Pretty tuff on jackets.
I've shot 150 Ballistic tips to 1400 yards plus and was pretty pleased.
Nosler and Hornady bullets are the best for not dusting even at around 3600 FPS MV.
The Bergers are working very well also.