"...big game hunting out around 500 yards..." Too far. At 500 yards, the .300 UM with a 180 grain bullet only has 2160 ft-lbs of energy left and it drops 27.3" with a 250 yard zero. The remaining velocity is 2325fps at 500. S'ok at 300 though.
http://www.remington.com/products/am...terfire&cal=38
Unless you've spent a great deal of time shooting at 500 yards and can hit a 9" pie plate every time, you shouldn't be taking hunting shots at that distance.