I use 36.0 grains of IMR4227 with a 320 grain lead bullet that was designed for the 50AE. I use magnum large rifle primers. This load limps along at just about 1000fps and is very accurate from my 8 3/8 inch barrel. It also does not lead up the barrel as the bullets I am using are a bit soft.

Congratulations on your new gun. I have found that messing around with the 500 is a lot of fun!