I hope recordings have been taken for indoor & outdoor, and most importantly, at varying distances.
It's probably impractical, but what I'd really like to see is completely different firing sounds depending on where you are relative to the shooter. Gunfire sounds different depending on whether you're shooting the gun, standing in front of it, to the sides, etc. You'd have to learn how each weapon sounds from every angle if you wanted to identify them by ear rather than just memorizing one sound.