Junk brass...
Herc 30--Good questions!
Pistol and rifle primers are all-brass. Don't deprime scrap brass; it is a waste of time. The spent primers, IN the cases, are just a little more weight of brass. FWIW, I'm saving up my removed primers from cases I'm resizing to reload--takes a Loooong time to accumulate any decent weight of 'em, but eventually they'll go to the scrap dealer along w/my junked cases, and I expect to be paid the same for 'em. The market for scrap brass is up, up, up right now, thanx to the Chinese demand for metals.
If I understand correctly, shotgun primers have steel in 'em, therefore are worthless as scrap brass, also as scrap steel. But I don't reload enough shotgun ammo to have the primers-as-scrap question matter to me, so haven't checked.
On live rounds found on the ground: I find a whole round or 2 every time I go to the range. Usually .22 rimfire, but not always. Sometimes the rounds have a firing pin dent (therefore are duds) and sometimes not (therefore are "drops," as the battlefield archaeologists call never-fired munitions they find.) Once in a while, one of the drops will have a mutilated bullet nose, indicating that it was a victim of a jam, but most were just dropped.
I used to fire off the live rounds if they fit my gun, just to deactivate them as a public service. Then I considered the danger of mis-loaded reloads, and stopped that practice. The gun club to which I belong has locked "dud cans" at each range, so now I just deposit all found ammo there. What the club does with it I do not know.
Most ranges will have some procedure for dealing with live-but-unusable ammo, but the practices differ.