Re: New and need advice
I don't know what your budget looks like, but if I were to start from scratch, I'd buy a Savage long action and go from there.
There is a fine article by Jerry Teo called I think: Long Range Rifles on a Budget. Just type in name or title into the search function and enjoy!
About caliber, there are many that will do what you are asking, provided you use superior ammo. Your caliber selection first depends on weather or not you reload, do a little research on this site and you will find one that should work for you.
In my humble opinion, more important than just the right equipment, is lot's of practice, I mean as much as time and money will allow.
Welcome, and I hope you get as much from this site as I have!