If you do it with atan, you'll need to modify the result by adding 180 to it in some circumstances and such. If some extension includes atan2 I recommend that one.
I once made a complete engine of a 360 directions bullet... it has flaws but I'm too lazy to perfect it. It's in french but you should figure your way around it. If you absolutely need a translation I might see what I can do for you...
http://sooda.dy.fi/~nuutti/jotainmuuta/rapid_32_bullets.gam
i did one too, i am not sure how perfect it is. it has 360 degree shooting now.
hmm, the file still has the name rapid 32 bullets, though it's not 32 directions anymore, it's 360 degrees.
Oke i implented the 360 shooting thing, and it works fine but now i need to create a machine gun and a shotgun, how can i create these using the 360 shooting system (machine shoots less acurate and the shotgun shoots 2 or 3 bullets in different directions) I really dont know how to do this, please help.