Greg, I've been shooting a factory Rem 700 short action, in 6mm Rem, since 1974. Well, my youngest son hunts with it now, but I still claim it from time to time!
Although the factory rounds fit fine in a short action, a lot of guys like to build them on a long action so that they can seat the bullets out much farther. This of course provides more powder capacity, therefore more velocity.
The .243 AI is also a wicked shooting little rascal. Either, or even the standard .243 Win, is dandy for varmints through deer size game. I don't recall ever shooting anything out at 500 yards with my 6mm Rem. Ours. Whatever! It will drop a mule deer just fine at 300 yards with a mere 95 grain Nosler Ballistic Tip. Complete penetration and devastating results internally. Typically we shoot 75 gr hollow points at rock chucks, 95 - 105 gr bullets at deer, and whatever happens to be in the rifle at coyotes.
Nice little cartridge. There's a lot of info on the various 6mm's - except not much on the 6mm Remington - at AccurateShooter.com 6mmBR.com -- Best Guide to Precision Shooting and Precision Rifle Accuracy
Check out the articles on the .243/.243 AI as well as the article on the 6XC.