[slowhandluke]

I always wondered where their casings were falling.

I don't think the A-10 dropped their casings, as it'd be big trouble if one got sucked into an engine. The casings are fed back into a storage bin.

[riverrunner]

I always wondered what happen to them

[MasterGunner01]

“I always wondered where their casings were falling.”

Airborne Gatling guns such as the M61A1/A2 (20mm), GAU-12/U (25mm), and GAU-8/A (30mm) use a link-less feed system that does not use links and re-stows the fired cases back into the ammunition drum. The reason is because high speed jets would shoot themselves down with any links and expended cases ejected overboard.