As to the second part of your request, I found a good deal of what you are looking for with a simple Google search.
I started with Google and searched for Debange Cannons. I got 1130 hits.
I started with
http://en.wikipedia.org/wiki/Charles_Ragon_de_Bange Lots of information there. Click on pictures, click on drawings lot of information found.
Encyclopedie Larousse Illustree copyright expired
Encyclopedie Larousse Illustree copyright expired
(French 155 mm model 1877 cannon, displayed in Hämeenlinna Artillery Museum. Photo taken on June 18, 2006. Source: Photo by me, User:Balcer. == Licensing == {{self2|GFDL|cc-by-2.5}} Category:Finnish Artillery Museum [[Category:Canon de 15)
(French 155 mm model 1877 cannon, displayed in Hämeenlinna Artillery Museum. Photo taken on June 18, 2006. Source: Photo by me, User:Balcer. == Licensing == {{self2|GFDL|cc-by-2.5}} Category:Finnish Artillery Museum [[Category:Canon de 15)
The last two pictures have a great source for you to follow up on the Hämeenlinna Artillery Museum. Here is a link to that museum.
http://www.tykistomuseo.fi/piilosivut/artillery_museum/ right in the middle of the page is an email address. Send them an email and tell them what you are looking ask if they might be able to help you.
Further on in
http://en.wikipedia.org/wiki/Charles_Ragon_de_Bange you will find a number of links highlighted in blue. Click on the links and you will be taken to sites with additional information.
Also from the Google hit list at the side you should see an option to select just images. Scroll through the images and if you see one that looks interesting click on it and go to the web page and see what’s there. Look for a contact for on the web page and send them an email and ask questions.
Just because you see one pictures don’t assume if you see it again that they are the same. Here is an example.
This picture
Will lead to this webpage
http://www.navweaps.com/Weapons/Gun_Data.htmOn the page use Find, Alt F or CTRL F and look for all reference to de Bange
If you scroll further down that list of pictures you will find another picture that looks the same, but isn’t.
Use you find again. If you try to find de Bange on that website you won’t find anything. If you look for deBange one word then you will find something. What I found was very interesting. This term “DeBange gas-check system” I put that term into Google and came up with a whole bunch more information.
One that was interesting was
http://books.google.com/books?id=rpwKAAAAYAAJ&lpg=PA481&ots=JEw0LLaBaU&dq=DeBange%20gas-check%20system&pg=PA481#v=onepage&q=debange&f=false A Supreme Court decision.
But then there s this one.
http://books.google.com/books?id=IHkDAAAAYAAJ&pg=PA37&lpg=PA37&dq=DeBange+gas-check+system&source=bl&ots=QUJ98Po_Wq&sig=QMRj5Xo_a6xggw24aRUYJmKVY9w&hl=en&ei=pDtLTfW6M47msQO7xISiCg&sa=X&oi=book_result&ct=result&resnum=6&ved=0CDUQ6AEwBQ#v=onepage&q&f=falseAnd the this one
http://books.google.com/books?id=zEhAAAAAIAAJ&pg=PA66&lpg=PA66&dq=DeBange+gas-check+system&source=bl&ots=PmhfLeuAf0&sig=_FGE2FUKr7v0dBuyChBRlUrqbbM&hl=en&ei=pDtLTfW6M47msQO7xISiCg&sa=X&oi=book_result&ct=result&resnum=8&ved=0CDsQ6AEwBw#v=onepage&q&f=falseOkay, I have shared with you my knowledge of internet research, now you have to build one of the guns and show me how to do the machining….