Our range has a bin for misfed or dud rounds.
They do not want us dumping misfeeds or duds
in the "burn barrel" with targets, jugs, plastic bottles etc.
I have burned old ammo myself: the bullets don't go far,
but the casings are miniature rockets! They won't do
much harm inside a 55 gal metal drum. if they do get
out, they are going up, or bounced off the side
of the barrel, and fall to ground harmlessly.
The best and safest thing is to pull the bullets, dump the
powder and even forget about recycling the bullets or casings.
As an experiment, I found that about half of .22 rimfire duds will
fire if you rotate the shell so the firing pin strikes opposite
the original firing pin mark on the rim: sometimes the
priming compund is not uniformly distributed in rimfire cases,
especially in the cheap bulk pack ammo.
I have also had old .303 military surplus rounds hangfire up to
a second, so don't be too quick to eject that "dud."