6.5-06 is a good choice. Then you can use any 30-06 brass you have although it will require trimming. I use 25-06 brass in my 6.5 so I don't have to trim. 400 yard is no big deal for this cartridge.
I agree with TS, as I have used 6.5-06 and 6.5-06 AI for over 15 years. It is no stranger to 1K, let alone 600 yds. 600 is a pot shot with the right set up. My wife regularly hunts with it throughout MT, and has never had an issue. Light recoil, under 26 MOA to 1K, hits like a truck on most game, and easy on shoulders. Complete set up is as follows;
•Weatherby MK V action
•Timney Trigger set 2.5lbs
•Hart 8 twist #5 finished @ 24"
•Winchester 270 brass formed, trimmed and uniformed
•Berger 140gr EH
•CCI BR2
•R26 (charge withheld) *start at what's reasonably warm for 6.5-06 A Square*
1 thou off lands and you'll fall in love shortly.
There are many good barrel makers out there, and quite a few good gunsmiths that can screw one on properly. Find the cleaning regiment that works for your barrel, stick to it, and map your cold bores each time you shoot. 'Quality in means quality out.' The finest rifle loaded with surplus ammo almost always yields surplus groups. Eliminate all the factors you can and problems are immediately identifiable when the occur. The 143 ELD-X is a nice projectile as well. And I have shot just about all of the aforementioned calibers and still own quite a few of them. I'm not knocking any of them, simply stating a preference for pure accuracy and ability to take sizable game with a fine caliber. I'm a projectile fan first! Cartridges are just luggage for powder charges. One final note, the 280AI is a fave of mine and I regularly hunt with it. Physics isn't just a good idea, it is the law. Bigger bricks hit harder than smaller ones when thrown at the same speed.
