.17 Incinerator
The .17 Incinerator is a novelty Wildcat Cartridge created by necking down a .50 BMG case all the way down to .17 caliber - a process which takes many steps.
Origins
It isn't entirely clear who originally created the .17 Incinerator. For example, Frank Barnes' Cartridges of the World (14th Edition) claims that it was first produced by a machinist named Zachary Weighman. His version is inert, and contains no power. The primer is simply from the original spent .50 BMG round. At the time, he sold them as a novelty for $20 at gun shows and it is noted that the finished piece has no cracks on the neck of the case.
According to Zachary Weighman, "I started making these up for friends of mine, after seeing a drawing of ‘Dingbat cartridges’—drawings of mythical cartridges. I thought they were really cool, so I started trying to figure out how to make them. As you can see, I did get it figured out.”