I've definitely learned a lot from fic, to the point where I've joined conversations with very obscure topics that puzzled my friends. "Where did you learn that?!"

"Uh..."

With military/tech stuff, I tend to take it with a grain of salt. I also don't mind if the author "fudges" details in this part of the story because focusing too much on realities, like radio chatter as Paul is pointing out below, just isn't as interesting a fic to me. One of the things you really have to keep in mind is your audience and your genre. If you're writing for hardcore military, then by all means, list specifications about the carbines and the weapons they're carrying. If you're not, you've got a little leeway. :)

(awww, baby Renner)