I owned a 20" Bushmaster with an A2 upper in the late 90s. It shot everything I put through it and was a great rifle. I ended up selling it and bought a new 16" Bushmaster with A3 upper in early 2009. Back in the 90s when I did my research, Bushmaster seemed like a quality gun, especially for the price. I neglected to do my research when buying the most recent 16", assuming (my fault) that Bushmaster was one of the better brands. Now that I'm doing some reading, I realize that there are a lot of brands that are much better quality out there. Now, I really like my Bushmaster - it shoots great and has been reliable, though I only have about 500 rounds through it and none of that is 5.56 (all .223 soft point). From what I've read, under heavy use the internal parts have a tendency to break as the rifle just isn't mil spec. My questions are: 1.) What parts are most likely to break, especially if I do a lot of shooting of 5.56? I'll probably want to get some spares of these parts. 2.) Are there parts that should be replaced up front because they're just not all that reliable? Any "fragile" parts that might break from a lot of use or if it gets dropped? Thank you for any help you can provide.