All sounds CC-by-sa Julien Jorge, produced with the following samples.

cannon:
CC-by gim-audio http://www.freesound.org/people/gim-audio/sounds/28645/

crash:
CC-by Sparrer http://www.freesound.org/people/Sparrer/sounds/50506/

empty-cannon:
CC-0 j1987 http://www.freesound.org/people/j1987/sounds/107806/

hit:
CC-by FatLane http://www.freesound.org/people/FatLane/sounds/92019/

tar-spatter:
CC-by FreqMan http://www.freesound.org/people/FreqMan/sounds/25819/
