Yeah the GUUs were apparently really inconsistent. Slick side, A1, and even A2 uppers, pencil or M4 style barrels, anything goes.
I'm no USAF expert and basically picked the GUU for a build because of the apparent ease of getting it "right" rather than any particular connection to the Air Force. My grandfather served in the USAF in North Africa, where he enjoyed his meals of camel meat and warm beer, but that was long before the GUU or even the AR period.
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