Here’s some useful nitty gritty via Chris the Story Reading Ape and Janice Hardy of Fiction University, from, in the end, Dave Chesson, of Kindlepreneur fame. All wonderful resources. This one serves those of us writing mystery/suspense who end up with those shootout scenes, maybe despite our better judgment. At least we don’t have to look totally dumb! Thanks to all on this team.
on Fiction University:
Having characters use firearms in a book can be common practice. There are some genres that use them extensively like science fiction, thrillers, crime novels, and more. However, regardless of what genre you write in, there is a chance that at some point, a firearm will be a necessary plot point, component, or a part of your next scene.
Writing about guns can seem simple since we see them a lot on TV and movies. However, the movies usually get it wrong, and this has caused many misconceptions that bleed into a lot of stories.
So as to help authors understand weapons better, and thus create stronger stories, I’m going to start by discussing major concepts and principles. Then I’ll show you some resources you can look to, as well as some ideas on how to investigate or do field work if you choose.
Just Can't Help Writing 