Pull the bullet out attach cryptic note to confuse your children in 30years.
Pour powder down toilet, throw case in bin.
You could drop it into a gun shop who will just do this, they might fire the empty case to get rid of the primer.
Don’t bother the police they won’t really thank you.
I started clearing out my late father-in-law's garage last night (a massive task) and found a live .38 bullet. How should I dispose of it?