A little while ago OutdoorHub covered the double-barreled 1911 pistol from Arsenal Firearms, and this is possibly the closest we will ever get to the same thing on the AR-15 platform. Demonstrated here by Tony Rumore of Tromix, this “Siamese 223” can handle a mag dump like no other.
“The latest and most insane creation by Tromix is this Siamese 223 for LAW Enforcement only,” states the Tromix website. “The synergistic exchange of gas tubes forces the expanding gasses from the lower rifle to the top rifle allowing it to cycle a cartridge into the top breach [sic] then fire when the bolt is closed. The gas from the top rifle is then sent back down to the lower rifle where the first empty round gets ejected and a new cartridge is loaded into the breach. It is a wicked wild ride when fired FULL AUTO.”
Tromix has also worked on projects such as a muzzleloader AR-15 and a bolt-action pistol. You can find more of their creations on their Facebook page.