Stateside in 1974, I never saw a 30 rounder until two years after I ETS from active Army (1979), and joined a USAF SP reserve flight. We had GAU-5/A/As with 30s. Later I got issued a GAU-5/P USAF "Franken Carbine" that was a 601 lower and upper, repurposed with a 14.5" 1/12 carbine barrel and a collapsable stock. We even had a green stocked 601 in the Arms Room. I shot it a couple times at range days. The Air Force always recycles and repurposes weapons.