I have a AR10A4B which I relaod for.
First off, do not contact ArmaLite as they will disavow any cartridge for the weapon that is not commercially produced. - Legal Libiality.
I have nothing to add to Mr Gilby's post except to say that all good practices for reloading for a gas-gun apply.
Next, pick up the book "The Competitive AR-15"by Glen Zediker. You may wonder, but nearly everything about loading for, and shooting an AR-15 well applies to it's bigger brother. And the general reloading insights that Glen outlines for AR-style gas-guns
in his book are INVALUABLE to the beginner.
Now, you are wondering, why doesn't somebody give me a decent load? Well, okay.
I get sub-MOA groups @ 100 yds. with this:
168gr Hornady BTHP Match, seated to 2.800" OVL 41grs AA2520, WW primer in mixed cases trimmed to 2.005 after full lenght sizing.
I use Lee dies and their "Factory Crimp" die *really* does improve accuracy.
This [Lee factory crimp die] was written about in one of last years "Shooting Times"
[? I think] magazines in an article about accurate reloads and the AR15.