Here a couple of interesting ones I found on wikipedia.
Ackley was not just a wildcatter, he was a researcher as well, often testing firearms to destruction in the search for information. He also produced a number of experimental cartridges, not intended to be practical, but rather to test the limits of firearms. One of these experimental cartridges was the .22 Eargesplitten Loudenboomer. This humorously named cartridge was developed by Ackley for Bob Hutton of Guns & Ammo magazine, and was intended solely to exceed 5,000 ft/s (1,500 m/s) muzzle velocity. Ackley's loads only managed 4,600 ft/s (1,400 m/s), firing a 50-grain (3.2 g) bullet. Based on a .378 Weatherby Magnum case, the case is impractically overpowered for the bore diameter, and so the cartridge remains a curiosity.[6] Another humorous round, the .17 Flintstone Super Eyebunger, based on the .22-250 necked down to .17 caliber, has been used by Australian gunsmith Bill Hambly-Clark, Jr. to achieve velocities of 4,798 ft/s (1,462 m/s) out of a 52-inch (1,300 mm) barreled gun.[4]