I take them home and disassemble the hull with a shell cutter, reclaim the lead, dump the wad and the powder and drop the brass and primer into a lidded quart paint can half full of WD-40. A couple weeks of soaking unattended ruins the primer and I discard the brass.
I use bullet pullers to disassemble old 5.56 and 7.62 rounds, recycle the bullets and soak the cases to kill the primers.
If its rifle ammo two ways. I have pulled the bullets and then melted the lead for shot. If you don't want to do that then take it to a bridge that is over water and dump it. If its shot shells then cut them open and get the shot and anything else you want then dump the rest. They will not go off on you if thats what your thinking.
<blockquote>"Your local law enforcement agency might destroy it for you. We had people come in with old ammunition and ask us to get rid of it for them. We were happy to help."</blockquote>
Our local constabulary isn't so accommodating. They told me that they have to document ammo destroyed as defective and they "can't be the disposal service for everyone with a bad bullet".
<blockquote>"I have read that once the WD-40 dries out the primer can be fired."</blockquote>
The one good thing about WD-40 is that it never dries out. That same gummy goo that it leaves behind in everything it's sprayed on is also what keeps primers from firing after a soak. And if the ammo wouldn't fire "in someone else's gun", I doubt it would fire in mine either.