Lots of good information here but since you are shooting a gas-gun some things require more attention. Adequate headspace clearance is critical with a semi-auto, typically I like to have at least .003 - .005 on my loaded rounds. Uniform primer pockets for safety, not accuracy - I use a tungsten carbide cutter from Sinclair. I've also noted that AR-10s are a little different from the M1A I usually shoot, they seem to need heavier charges of slower burning powders to function. I use IMR-4895 and H-4895 in my M1A but had to go to IMR-4064 to get my friends S&W MP10 to function. Semi-autos are pretty hard on brass too, so I prefer military brass such as Lake City, IMI, or the new Starline Lake City equivalent.

If you don't have it, this pdf by Zediker on loading for the M1A explains a lot.

http://www.zediker.com/downloads/14_loading.pdf