I've always wanted to try these, but can't speak from experience... http://www.brownells.com/.aspx/.aspx...M4_Pistol_Grip
Edit: Also, here is a nice article with a listing of AR grips with photos of their profiles in case one of these looks like it would work for you. The Sierra Precision perhaps.
http://gearscout.militarytimes.com/2...gallery/page/2
Bookmarks