People at the firing range I go to leave their brass and others pick through and take the ones they want for reloading...leaving metal isn't littering to me...leaving paper targets and other garbage is littering though.

We take cases of soda to blow up, beats a paper target unless you are sighting a gun in for the first time...there's no way to pick up all the shrapnel of the exploded cans...and tannerite just evaporates after the explosion.