A grouping of 0.556″ at 100 yards is nothing to cry about. I’ve not done much long range with my AR, but I don’t know that I’d have his level of accuracy. My AR-15 is a low-end, no frills model, and the LaRue models are pretty much the top of the line.
If you can be in the Liberty Hill, TX area on October 16th, LaRue is having a range day from 10 – 5. Guns, ammo, and food provided at no cost. Plenty of prize giveaways as well. If I wasn’t going to be out of town, I would be there. Hopefully I can attend next year. You can go to http://www.laruemedia.com/RangeDay/RangeDay_Home.htm to find out more details about the range day.