The .22 Tuba (and .22 Tuba II) is a wildcat cartridge created by machinist Zachary Weighman, in both a rimmed and rimless version. The initial model, the ".22 Tuba" wasn't a working cartridge at all, just an oddity that Weighman has machined for fun. However, he later developed actual working cartridges, which he called the .22 Tuba II. The rimmed version was based on a .44 Magnum case, and the rimless version was based on the .45 ACP.
Development / Origins
Zachary Weighman explains his development of the .22 Tuba and .22 Tuba II in Frank Barnes' Cartridges of the World:
“I started making these up for friends of mine, after seeing a drawing of ‘Dingbat cartridges’—drawings of mythical cartridges. In one of them, the shoulder started at the rim. Being a machinist, I decided to turn up a few of these from solid brass. I gave them a primer pocket and drilled out the neck, too. I seated snapped primers and bullets in them. Being as how I’m a cartridge collector, I have lots of friends who think this kind of stuff is pretty cool, so I made them up to give away to my friends.”
“One day a friend said, ‘Wouldn’t it be cool if you could make up an actual cartridge like this?’ So, after giving it some thought, I decided to make up a die for necking down a .45 Long Colt case, to see what it would look like. The die has inserts that progressively get smaller. It took five sizing steps to neck the .45 LC cases down to .22. I had moderate success with this, but I did not have a lot of .45 LC cases on hand. However, I did have lots of .44 Magnum cases, so I changed to them. After refining the process a bit, I was having much better success with these. I later decided to try using .45 ACP cases to make a rimless version of the .22 Tuba. I decided to call my cartridges the .22 Tuba II.
“At this point, they were still just dummies for giving away. Once again, the same friend said, ‘It would be really cool if you had a gun that would shoot these cartridges.’ I had an old Marlin single-shot .410 bolt-action shotgun. Because the head of a .410 shell and a .44 Magnum cartridge are very close to the same diameter, I thought the action would work. It was just a matter of changing the barrel and cutting a chamber. So I removed the .410 barrel and installed a .22 rimfire barrel onto the action.”
Weighman continued, “I had already cut the chamber into the barrel, using drills and lather tools on my lathe. The whole deal worked really well. The extractor even worked with no other modifications. Then I turned to the rimless version. With this, I decided to use a single-shot .410 shotgun again, but this time it was a break-action New England Firearms gun. I cut the barrel off at about seven inches, creating a sort of mono-block. Then I drilled it, reamed it, and threaded the inside of this mono-block. I then took another .22 rimfire barrel and threaded the outside area to match the threads in the mono-block. The barrel was threaded into the mono-block and, after some extractor work and adding a scope mount and scope, it was ready to go.”