Hmmmm? I do several that are just fire formed from not-so-obsolete parent cases like .30 Remington (I bump it up to .32 and down to .25), and .348 Winchester, which is the parent case for lots of old stuff. I've rim turned, and cut extractor grooves in .30-30 brass to make .32 Remington, and turned down and sized .223 brass to form 7.62x28 Nagant pistol brass. I broke the frame on a Lee single stage press doing that. RCBS Rock Chucker watched that press come and go. Never complained, or felt neglected. I swore after the first 50 of the .223 to Nagant conversion that I'd never do it again, but for some reason I'm finding that those old converted cases shoot more accurately than any other Nagant brass I've tried. Without knowing it, I accidentally created a new unofficial caliber when making brass for a 10.4mm Italian Ordnance revolver. (The least ergonomic pistol I've ever fired, but it'll put lead on target at 100 yards, point of aim = point of impact!) This was another one that was offered with a laugh. "Hey, want to buy another pistol you can't get ammo for?" The result of making brass and sizing bullets in the cylinder that would fire was a slightly tapered case with a .422" diameter bullet. After I finally located some genuine 10.4 Italian Ordnance cartridges I found that they were actually bottle neck cartridges. Probably for ease of loading, but side by side these were clearly different cartridges....so I dubbed the tapered case the ".42 Special." I can only remember two cartridges that have no parent case that they can be converted from. .22 Hornet and .357 Maximum. There are surely more, but those two were humbling, because I was sure I could make them from something. Tube and bar stock would do it, but even I'm not looking for that kind of challenge.