Re: Deer hunting at 500 yards with a .243?
A longer barrel would be a good thing, but I would expect an accurizing job to make a big improvement, even without a new barrel. One good place to talk to would be Hill Country Rifle.
As far as the .243 at 500 yards, I is up to the task. Just need to put bullets where they need to go.
I would suggest a minimum standard of 1 MOA for deer at 500.