I'm not a gunsmith and can only speak from experience - I've shot literally tens of thousands of rounds through my 1911s. I've been told that the extractor was designed to feed rounds up from the magazine. That is, the rim of the cartridge comes up and under the extractor. The extractor, I'm told, was not designed to ride up over the rim as would happen if you put one in the tube and let the slide forward. I don't know if your procedure would damage or shorten the life of the extractor, but given the finicky nature of the extractor I would refrain from the practice.