I found that a decent single point sling (http://www.blackhawk.com/product/Storm- ... 0,1342.htm) with the pistol held firmly against it made me more accurate than a cheek weld. A Magpul Angled Fore Grip helps too...and is legal to mount on a pistol.
In the end, I make the mistake of shooting someone else's RRA PDS - http://www.rockriverarms.com/index.cfm? ... ory_id=441
I got sold on the no buffer tube piston system...YMMV though. AR pistols are sweet range toys.