Turrets get a warm-up period after being placed.
Mods introducing new content into the game.
New ways to deal with enemies, be it attack or defense.
This will lead to guns not becoming active in SP and desyncs in MP
If you're not sure how to fix this, here is where you can find out about the global table which is where you will want to store your data in order to make it properly save between loads and different multiplayer clients :)
Bug #2 in data.lua
If your animation speed is 0 the "sound" entity will stay on the map. To fix this just set animation speed to 1
Bug 3 Hard coded player surface instead of entity surface in Play_sound
I fixed all the bugs and added some comments in the code so you can follow what is going on, feel free to check it out. https://drive.google.com/open?id=0B8Bwv5pIO0rqYUU0dmczaFFsSVk
Fixed it. Thanks for the help!