Going back into the early 80s there was a shop here in Milton, VT there was a provider of reloaded and obsolete caliber ammunition. I was privileged to know the owner, Ira Farnsworth (RIP). He was an active benchrest competitor, gunsmith & overall good person.
I worked in his shop for quite a few years, when the serious shooters stopped by it provided a whole 'nother level of shooting education both in shooting matters and converting available cartridge cases into usable cases for cartridges no longer being made.
It was rare that Ira ever had to throw in the towel on a cartridge conversion. One that I saw stump him was an order for .333 Jeffrey ammunition. There was nothing available that would be quite "right" in one manner or another. I don't remember how many hours we did put into that project but it stretched into months with making test runs, sending them to the customer and finding something wrong. I didn't know all the details that must have been discussed with the customer but it was right around that time that BELL came out with another Jeffrey case(.400, maybe .450 Jeffrey?) that WAS the correct feedstock for the .333 and I think he ended up buying that to convert.