Sorry for the link to YouTube, but the video is quite interesting and full of Patriotic goodness! This is a replacement upper receiver that allows you to fire soda cans, and other projectiles. GREAT video - well worth the couple of minutes needed to watch it.
https://www.youtube.com/watch?v=HfHPp-6SyD4
Link to product:
https://xproducts.com/product/can-cannon-soda-can-launcher-ar-15-m16
Enjoy, my frens!