Generally called "firing". Your link doesn't work for me so I can't talk about what is on it.
However, you'll have to do better before concluding anything.
BTW I think this site knows more about it than you or I and they refer to your "shells" as rounds, and when all is said and done a 30mm cannon just fires big bullets, or in correct military terminology "rounds".
https://www.airforce-technology.com/projects/a-10/?cf-view&cf-closed
I surprised you didn't mention Puff The Magic Dragon as that had actual artillery on it, but were you even in the armed forces to be trying to correct me?
BTW, here's an article about Puff, and please note the terminology used when referring to using the weapons.
The guns to be active for firing
https://en.wikipedia.org/wiki/Douglas_AC-47_Spooky