Anyone heard of a US experimental project where a 20x110mm case was necked down to use .50" projectiles? I recently saw one at a small gun shop near here. The story was that it was an attempt to get a flatter shooting cartridge for the M-61 “Vulcan” gatling gun. Since there is a test range nearby where G.E. used to fire these guns, it makes sense that a stray cartridge found it’s way into a local gun shop collection. The shop owner is a strange guy, so I was unable to look at the cartridge or get a headstamp.