I know this is an odd post, but calling Smith and Wesson's customer support line is helpful, but when you need the man; you ask for Albert "Al" Sholsser. Al, is the subject matter expert for the M&P 15 series rifles, he builds them for you and me. Not only is he knowledgeable, but a very friendly (talkative) guy. If you need help, or have a suggestion Al is the one to talk with, chances are he will have the solution to your problem before you get off the phone, or he will call you back with the answer. Just thought I would give him a shout out...