Earlier quoted context omitted.
my understanding is that most allow the discharge of firearms, for fun or hunting.
I live in a national forest. At least here you're right. But I assumed OP just meant it's not smart. If you go into the national forest around me and a warden or ranger finds you shooting a gun you will be charged for poaching.
As a rule of thumb, if you're shooting guns in the NF and aren't engaged in legitimate, licensed hunting, you will be suspected of poaching.
This is also a thing that can vary a lot, depending on the specific area you're in.