My friend Andy, who is a design engineer, provided this link. I'm going to try and find some old breechloading cannon patents on it, those I haven't found elsewhere. In most cases, all I have is an inventor's name I saw in Army or Navy ledger books in the Archives, and a rough timeframe, so I don't know if the designs were ever formally patented or not.
http://www.irossco.com/patentsearching.htmThe only problem, which is a big one for me, is that if you want to search US patents before 1976, you have to have the patent number, or date, and or exact current classification, or something like that. In 1976 or after only, you can search using more info like inventor's name.
Google patents however does search way back to 1790 using sparse information such as inventor's name. Their database is expanding but apparently isn't perfected yet. Still it is pretty good for online searching of the old patents where all you have is a name or maybe you want to see all in a certain classification and date range.