I shoot on public land all the time. I also have a "leave no trace" policy for myself and whomever I'm shooting with.
Brass, soda cans, shot-up targets, perforated living trees - all of that stuff can have as much of an effect on policy change as the gunfire itself.
I did have an encounter once when I was getting out of my 4x4 at the same time the county search & rescue team was getting ready to launch a training exercise. One of the team members tried to tell me that we couldn't shoot in the area (he was non-LEO). I said "you want to bet?". His jaw dropped. Pretty funny. Then I asked the team leader which way they were going and I said we'd go in the other direction. Problem solved.