The300 Weatherby shoots incredibly flat. That said, you will be surprised at the level of recoil and muzzleblast you will experience with that cartridge. Sight it in so that you will have a +/- 4" MaximumPoint Blank (MPB) trajectory and you wil be within a deer's vital area out to 400-500 yds.
to my knowledge remington and winchester do not make ammo for the 300 weatherby.
Remington does, I was surprised when I saw a box of it last week.
Go to JBM http://www.mega.nu:8080/traj.html
to do your ballistics calculations. Just a hint, the site does not care what cartridge you are shooting, it just looks at specific bullets at a given velocity.