Which means it is actually a .308 necked down to .224.
Unlike most .308-based cartridges, the .243 uses some unique dimensions. It can more easily be considered its own cartridge, than many other .308 offspring.
If you're going to get that technical about it - you need to just say it's a .300 Savage, lengthened, and necked down to .22 caliber. Or... it's an 8x57mm Mauser, shortened, and necked down.
The .300 Savage was the original parent case for the .308 Win.; not .30-06/.30-03, as most people believe.
And we all know where every one of those modern rimless cases has its origin: the 7x57mm/8x57mm Mauser.