Bullet Collection 1 (M484), Master184 (http://opengameart.org/content/bullet-collection-1-m484)
Licensed under CC0 1.0 Universal (CC0 1.0)
https://creativecommons.org/publicdomain/zero/1.0/
"Hitman" Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0
http://creativecommons.org/licenses/by/3.0/
Ground, Nekith (http://opengameart.org/content/ground)
Licensed under CC0 1.0 Universal (CC0 1.0)
https://creativecommons.org/publicdomain/zero/1.0/
"Gun Fire Sound", GoodSoundForYou (http://soundbible.com/1998-Gun-Fire.html)
Licensed under Creative Commons: By Attribution 3.0