That'd be quite true. There are any number of places on the Internet where the subject is discussed. I believe that there's a thread on FR entitled, "The Art of the Cache" that is very educational (article and FR posts both).
On a separate note, a large collection effort would require informants. People that dislike a gun owner. Heaven forbid if some of them were careless and left their empty shell casings or, EGADS!, live ammo from military caliber rifles on their property. Why, then they themselves could be informed upon and dragged away like the rest of the eeeeviiiiiil gun owners. That'd be TERRIBLE wouldn't it?
The answer to that is to go and drop some ammo casings on all of your immediate neighbors property fence lines. Wipe the casing with alcohol first and wear gloves.
Get it so common that nobody is alarmed when the little tots come home with a brass casing in their pocket. :~)