Ken King said:
Could have been a different gun variation, but I think the GAU-8/A is the "normal" configuration and it doesn't spit the casings out. And the rounds had aluminium alloy cases in place of the traditional steel or brass.
Almost all casings (other then small arms) went to aluminum in the early 80's, but shell casings are still referred to as 'brass'. The 105mm for the M60 (tank not MG) were brass until about 82, and those casings were prized possessions after they went to Aluminum.. Shiny aluminum just doesn't look as good as brass does as an umbrella holder/ashtray/ flagholder/paperweight. When the original M1 came out they were all aluminum casings, the 25mm for the Bushmaster on the M3 were all aluminum, but it's hard to tell as they were all painted green. When talking about the size of a 105 round the cost between brass and aluminum would be substantial, as would 1400 rounds of 30mm...
Now they have developed caseless tank ammo, no casings at all from the 120mm on the M1A1 except a little aluminum plate that gets ejected onto the floor after firing.
Looking at this picture I'd say you are right, the gun is firing, but no signs of any brass (and it's a linkless feed system so there wouldn't be any links or belts)
<img src='http://www.mabarn.ang.af.mil/Pics/676W1905.jpg'>