I finally got a good enough look at a picture of an AR-15 bolt to figure out how that direct gas impingement works. And I generally agree with Klaus that a piston would be much better. But being as there are other advantages to the AR-15, I was wondering how bad the system really was, as in how much fouling do you get and what does it take to clean it? I expect an AR to be one of the last rifles I buy, and SHTF is last on my list of reasons for it. Among my accessories would be a 300 Whisper upper, and maybe pistol caliber conversions.