( Resurrecting an old thread here, but I found this by searching for old threads and decided to post here, rather than starting a new one )
Google Patent search has many old patents on-line, including firearms related patents. I think the Google search engine is US patents only, I think?
This is useful because the Google Patent searches allow full-text and diagrams to be shown for older patents (a USPTO on-line search can't show older patents fully).
Here is a link to Georg Luger's patent for "Recoil-Operated firearm"
http://www.google.com/patents?id=F5FlAAAAEBAJ
You can view on-line or download a PDF. Probably many other Firearms related patents but this is just one example.