Whether you want to finish out a new build or trick out an old friend, it's the little things that make a difference. Of course, the BCG, trigger, barrel, and furniture do mean something, however, the small touches do have a big impact. Just what good is your new wand of destruction if you can't bring it to bear? Let me tell you, without an AR castle nut your whole game is shot.
Have you ever pulled someone out of a ditch? How about started a job and bought just enough parts to get it done? From experience, I can say that you will be going back and getting more stuff. Why, because just what you needed isn't usually just what you brought. True, all that AR castle nut has to do is to hold the extension tube onto that lower receiver, but will it do its job?
I know that when I was younger, I jumped out on a wing and a prayer. Now that I have some miles on me I can't do that anymore. I have to know that something as small as my Nickel Boron castle nut is going to do its job. Just think about the force behind the shot, that is just in front of your irreplaceable eyes. Honestly, shooting glasses be damned, if I can't see then I can't shoot. I want something in the line of a Nickel Boron castle nut, locking everything in place so that I will see what I shoot after the fact.