The extractor may be keeping the cartridge from chambering. The extractor is supposed to be centered on a tiny ball bearing that is under spring pressure. It is supposed to slide outward enough for the cartridge case to slide past and then snap into the groove. Look at Youtube and search for removing the extractor. I use a sandwich bag to keep the ball bearing from flying into space. You might be able to remove the extractor and insert the other end of it and get it working.
