OK...only question the article didn’t answer for me was whether this was blowback or gas operation. I’d think there was potential for serious crap building up in the gas tube either way.
They're blowback. Note that some of the .22 pistol versions of the AR, such as S&W's MP15.22, work just fine without a buffer tube or carrier rweturn spring. the same is true of most of their full-length brothers, excepting the USAF M262 training conversion, which indeedc has provision for the miniscule amount of gas from the .22 round to be vented through the barrel's gas port into the front of the conversion.