This is my first AR-15, I think I did well. I am looking for detailed information about this particular gun like the size and weights of all the parts that make up the gun, for future reference when I want to replace parts. Anybody know of a book(s) or website(s) that spill the details of this gun or similiar guns? Also, do I need to carry any spare parts on hand and where can I get parts for a resonable price besides SAW? Also, thinking about buying a second AR, looking at the LE6721, what do yall think? or a 20"?