Check into the 6 BR fast twist. It has got to be the most efficient 1000 yard gun going right now, so you can imagine how well it does at half that distance! Also, there is no fireforming, and the brass is almost good enough to just pull out of the box and load if you're not too anal like me!
Check out the ballistics on it, you will see that it gets about 80% of the velocity of the .243 fast twist with almost half the powder.
Look at www.6mmbr.com
under competitions, varmint hunting, and load data.
Shoot the fly off your target!