Well we can't know exacteley , since we do not know wich direction your turret faces.
Try:
OnActivate>Self>SpawnProjectile>[Projectile] [0] [100] [0]
And if that makes it go the wrong direction , take:
OnActivate>Self>SpawnProjectile>[Projectile] [100] [0] [0]
if it still doesn't work , take the 2 examples above , and put a - infront of the 100.