Re: Remington M24 info
I assume the other caliber you're talking about is .308 Win AKA 7.62X51 mm.
The M24 is built on a Remington 700 long action, and can be chambered in either caliber.
The U.S. Army is currently converting many of their existing M24s to .300 Win Mag, so it's a capable platform in that caliber as well. However, I think most of those conversions are going into an AI chassis system rather than retaining the stock.
Since you ask the question, I'd recommend that you start with it in .308. It's a lot cheaper to shoot and barrel life is longer than .300 WM. Later you can convert it to .300 WM if you feel the need.
Personally, I'd go with down rather than up from there, to .260 Remington or .243, but that's your choice.