Choose a direction.
Augh -- you would ask just as I'm trying to straighten out my files....
And now Amazon's hidden their "Advanced Search" feature as well. Okay, from memory, then.
The Writers Digest series is pretty good, though double-check any key info you extract for your story, as I've heard some dark mutterings about "facts" sometimes being based more on misremembered Perry Mason episodes than current science.
The Diagram Group used to have a very nice large hardcover that traced the evolution of the firearm with useful comments & good illustrations. It's enough to make you authoritative about a wide variety of handguns & rifles, & doesn't "geek out" with technical terms.
If you've got a particular manufacturer in mind, there's usually at least one book for each.
Ah, good -- I just found one of my crime-scene notebooks. A title that might be useful: Vincent DiMaio, Gunshot Wounds: Practical Aspects of Firearms, Ballistics, and Forensic Techniques
I've got a list of related books & videos, including more than you'd ever want to know about bloodstain pattern analysis. Lemme know if that'd be handy.