Goal is a 6mm to drive 70 bt's and 75 vmaxes 3700 plus, 1500 round barrel life at least would be nice. Both calibers have excellent brass available, lapua. Barrel length 27-28 I already have a 1000 yard rifle so I' looking at 600 yard and less mostly. I have a friend with a 40x in 6mm remington that drives 70 grain ballistic tips to 3720 and is the most devastating thing I have ever seen on crows. I want to match or exceed the detonation of crows I've seen w/his rifle, and have better brass available, .500 accuracy will be fine a touch more is always better. Of lesser importance, it would be nice to be able to shoot a little higher bc bullet if I wanted to play on steel to 1000. What would be the heaviest bullet I could stabilize with a 12 twist, 10 and 9? What are the pros and cons of these 2 cartridges shooting the varmint bullets.? What twist would be best for what I want? Put your 2 cents in on a 6mm-06 AI or 240 Gibbs while your at it. Look forward to hearing what you have to say about this.