If you have a lot of ammo horded (as you should) then I’m sure you have a few steel surplus ammo cans too. I recently stumbled upon this kit that allows you to add a padlock to your old steel ammo cans. They’re a good way to add extra safety to your old ammo cans. The hardware kit works with 50 cal, 30 cal, 20mm and 40mm ammo cans.
The kit is available with free shipping over on Amazon.com.