There are certain firearms where it's doable with the addition of a centerfire rifle receiver, I know it can be done with a rechambered H&R Sportster 17hmr or 17M2 barrel that's been fitted to an SB2 frame, the ejector notch just has to be modified and a 223 ejector/extractor installed, Larry (trotterlg) made one, although his strung vertically badly, so it wasn't the best conversion.
Tim