Take a look at what Pat (Scenarshooter) did with a GAP Non-Typical in .260:
http://24hourcampfire.com/ubbthreads/ubbthreads.php/topics/6856648/1I will also echo the sentiments about the .300 RUM. It is most definitely a caliber for a well seasoned shooter.
The two I have owned ( 1 Model 70 Winchester and 1 700 Remington) both had more felt recoil and muzzle blast than my .340 Weatherby.
If you must go .300 Magnum go with the .300 Winchester or .300WSM.