I just ordered a 219 .22 Hornet barrel from a member of Colt Forum that has been rechambered to .219 Zipper. It came to the owner with a 219 .30-30, and he apparently never shot it, although he bought some factory ammo for it and also some primed brass.
For $100 total including shipping, I figured it was an experiment worth trying, especially since "Mr. Single Shot" (gunsmith and gun writer Frank de Haas, RIP) says the action is OK for this caliber. Not sure if it is grooved or has scope mounts, but I'll figure that out.
I'll try any loose factory ctgs. if there are any to see how it functions, then load 40 or 45 gr. Hornet bullets into the primed cases and try it for accuracy. If it's OK, then I'll start scouting around for a supply of Zipper cases for the future. I'm sure somebody makes them from .30-30 cases, since this was a fairly popular varmint ctg. among single shot nuts back in the day (and there are a few of US left!).
If he includes any complete box of factory Zipper ctgs., I'll sell them to a collector and recoup some of my modest "investment."
If it won't group, or I get bored fooling with the Zipper, I'll have Sonny France or somebody else reline it back to .22 Hornet, since the outside looks new and I have a blank extractor to fit.