I was watching a show on History channel last night about the M-16 and towards the end they covered possilbe replacement options including the HK-416 which uses an AR-15 lower but has a much cleaner upper. Then doing a quick search I realize, we can't get those in the U.S. or at least I'm not aware of a kit or anything. I'm wondering what the options are for a cleaner AR-15? Are the HK-416 style gas operation and the ruger SSR-556 gas piston operation the same thing? Are other options available? I like the AR platform and the virtually unlimited accessories available, I just know how dirty they can get after heavy usage and I'm willing to spend a little more to avoid that. Thoughts?