Re: .280 Improved to what?
You can use a 280. I would reccommend the Sierra 168 MK or the Berger 168 or 180 VLD as far as bullets are concerned. You should have no problem knocking over the 500 Meter Ram with that combo.
The 280 is not too much as long as you are used to the recoil and can put 50-60 rounds through it at a match.
The best thing to do is enter a match with your rifle and give it a try (you'll love it)and see if the rifle needs rechambered.
My two cents anyway.
Learn from others mistakes, you won't live long enough to make them all yourself