3-9x is the most you will need for that caliber and barrel length IMO. A look at velocities on Hodgdon's site, with a 24" barrel, and you'll be using a 16", I think 300yd shots are a bit optimistic for that caliber for deer, but that's my 2 cents. In reality, I think 2-7x would be a better combo for you. If you want more range, either step up to an AR10 platform, or go to a bolt action. I'm sure I'll get flamed for that, so flame on, I just don't consider that caliber as well as similar ones legit for long shots on big game, ethically speaking.