I am fascinated by firearms, and have collected an extensive library of books about them. I am considered by many people I know to be an expert on the subject.
One of the books in my collection that may be of particular use, Small Arms of The World (1968), has specific instructions on how to load, fire, field strip, and perform maintenance on a wide range of guns ranging from WWI to the middle of the Cold War.
I am always willing to answer any and all questions relating to firearms, and am available to act as a firearms consultant to any mod team that could use the help.
If any mod teams are interested you comment on this post or PM me here on ModDB.
-Wing0Black Out
Even how to make a gun w/o attracting any attention when buying required materials? :-D
I should begin by saying that I am in no way responsible for how anyone uses the following information, and I do not encourage or support any criminal activity.
In response to your question, the answer depends on the type of ammunition you intend to fire; if you have a ready supply of standardized cartridges the process of creating a device to fire them is relatively simple, however purchasing more ammunition is likely to attract unwanted attention. Your best bet would be to make a muzzleloading firearm using homemade projectiles and homemade propellant (guncotton for example), such a device could be constructed from materials found at any hardware store.
Again I state that I am in no way responsible for how anyone uses this information, and am not encouraging or supporting any criminal activity.