Bert H. wrote:
There is "no one book" that adequately (or accurately) covers all firearms and their history and value. It takes a small library to do what you are looking for.
While true, let's see if we can be slightly more responsive...
There are _two_ books which cover 20th century firearms pretty well when taken together, the Blue Book of Gun Values, and the Gun Trader's guide. Unless you are interested in guns introduced -last year- between these two, you can pretty much get a handle on 20th century weapons. A three to five year old copy of either can be had on ABE.COM or Amazon.com for under ten dollars.
For guns prior to the 20th century, again there is one book that jumps ahead of the rest, "Flayderman's Guide to Antique Firearms." It's not comprehensive of course, but it covers the most popular, the ones they found most interesting, and most common guns. And, once again, a three to five year old copy can be had on ABE or Amazon for nearly nothing.
Like the CRC Handbook of physics and chemistry, the descriptions in these books don't change, any more than the density of aluminum changes. There's always new things, but my 25 year old CRC has a perfectly useful table of metallic densities and my five year old Flayderman's lists antique Stevens single shot pistols...
Having said that, guns are like cars, you can get a quick overview of the field from a Blue Book... but if you want to get into the details of the variations of the coachworks makers for Duesenbergs, you end up developing a specialists library. Similarly, if you're interested in Stevens guns, you will start out buying "Stevens Arms Company History" by Joe Vorisek and then assembling a collection of original and reprints of Stevens and Savage catalogs, Cornell's reprint of Steven's classic 1908 "Guns & Gunning" etc etc.
On the other hand, if old shotguns are your thing, you'll end up springing the $120 for Vorisek's three volume, 1600+ page opus "Breech loading shotguns 1860-1940."
A good place to start looking at what a gun reference library would look like is here: http://www.cornellpubs.com/old-guns/reference-books/
These aren't _the_ definitive collection either, but Cornell's reprints are inexpensive and as high a quality as can be done with current tech at a reasonable price.
Never-the-less, if you're interested in gun values, you would be silly not to spend around thirty bucks and get those three used from an on-line seller.
So, that's the answer.