Given that they are noobs, my guess is the “cannon” was a .45 ACP.
Lots of comments but the one that should matter is, that’s 3 more people who the NRA should be reaching out to.
I really don’t care what they fired, the name of the weapon or caliber. They tried something that most liberals are afraid of and they had a good time doing it.
Hats off to them.
I was at the range with my Boy Scouts once. A guy lugged his gear up. The first thing he takes out is a huge round and puts it on the stand. Everyone immediately moved away from him.
It was a 40mm AA round from WW2.