[Begemot]

Yes. According to Barnes & Skinner's "Cartridges of the World," the .450 was used as a light target load in British arms chambered for .455 Eley and Webley. That book is online, so put it in a search engine and have a look for yourself. Interesting read on the subject. I would add, however, that .450 is probably even scarcer than .455 and if you have original vintage cartridges you'd probably be best off auctioning them to cartridge collectors rather than firing them -- both for financial and safety reasons.