Lengthy "historyof the machinegun", from: HyperWar: The Machine Gun Very, very complete as far as I can tell. I really enjoyed it, although the "introduction" is rather off-topic it is setting the stage for the eventuallity of the self-feeding, self-cocking, multiple shot weapon.
That Hyper War site has some amazing articles. One could spend months examining it, and still not see it all. Here's a starting point, but it mainly seems to cover theaters of operation, although they seem to be working on a topic index, which would make finding things easier. HyperWar: World War II on the World Wide Web
Are you actually working on transcribing the PDFs to HTML? If so you are a true hero! I have the PDF scans and that is a great reference, but a fully searchable version would be fantastic.