Believe it or not, an ammo box can still be of use to you once its rounds are gone. You can use it for storage, as a toolbox, or possibly even as a Faraday cage. But if you want to use it as more than just a container, why not turn it into a portable set of speakers that you can take with you anywhere?
The ammo can speaker pictured above was made by Instructables user Dustin White. He started with an empty .50 cal box, though you could probably even use thinner 5.56 or 7.62 mm cans. He removed the plug for the power supply, and cut holes for two 4-inch speakers. Then, he added the audio jack and mounted the speakers, using a foam egg carton for sound insulation.
For complete instructions on how to make your own, check out his project page. Dustin isn't the only person who's done this, though, and you can customize it any way you want. Here's a similar one from Instructables user jimmuydean602:
Below, Zach (Vacca Rabite) over on 914World used a German can that was a little bit bigger than the standard NATO 7.62 ones. He stenciled on the design and put the volume knob right in the middle of the radiation symbol.
Want something a little bigger? Try the Quad Ammo Box Speaker by Laika on DIYStompboxes that's powered by a Ruby Amp and enclosed in not an ammunition can, but a wooden crate that housed small arms primers.
Or, if you don't want to make an ammo can speaker yourself, you can always buy the Thodio A-Box that the original project was inspired by. But beware, these aren't cheap. They run from $320 to $450, so you're better off making your own.
Have you built a speaker system out of an ammo box? Show us!