Hey all I am slowly building my AR and want to put this Magpul ACS stock on it. ACS™ - Adaptable Carbine/Storage The question I have is what other parts do I need to put this on the AR. Let's just say the AR is complete minus any type of stock assembly from the rear of the upper receiver back is missing. I am pretty sure all I need is a receiver extension, buffer, and buffer spring. Is that all? I am going for best of quality on this and is commercial or mil spec better? Examples??? One last thing that's extremely important, as well, is I live in NY and how do I go about getting something like the ACS pinned? Thanks everyone I really appreciate it sorry if this is any kind of repost!