Are you back yet?
This was in the early '60s, and so, before your time, but have you ever heard of a cartridge called the .22 JGR?
It was a wildcat, developed by a Canadian , John Gower, who had a shop in one of the eastern provinces, called John Gower Gunsports ,Ltd. There was an article about it one of the gun magazines. I carried that article around the world with me for years, until it became lost in a move.
Mr. Gower somhow modified .22 rimfire rifles, and the round would work through a standard magazine, IIRC. He used some sort of pistol brass, probably .25 ACP, and necked it down to .22, probably with a one diameter neck, and did some machining. He offered conversion services, brass and dies.
I thought that sounded like a really practical little caliber, but finishing my military obligation, 2 1/2 years in Europe, then College got in the way.
It never caught on, and of course, improvements in the .22 Long Rifle, Like MiniMags, Powerpoints, and Velocitors since then have more or less eliminated the need for the neat little caliber. Of course, the .22 Hornet, K-Hornet, and .221 Fireball would be more practical, I think.
Hmmmm..... Being a machinst and all, d'you suppose it would be possible to modify a spare Ruger 77-22 barrel to a .21 Fireball? They already do the .22 Hornet on the same chassis, so, the K should be a snap! But that Fireball? What do you think?
No, No, forget it! BAAADDD idea!
Oh, well: just got handed my head on another forum for asking such a stupid question. The Fireball and Hornet are centerfires, with the barrel threaded and screwed into the action, and the bolt is different. Another one for the "It seemed like a good idea at the time..." list.
When you get to be owner of your own firearms company, maybe you will save a little space among the Lasers, Phasers,and directed energy beam weapons for the lowly .22 Long Rifle, and its stone age family.