You could try this, if you want to have more control:
<img src="http://666kb.com/i/cihmto2saxov0tc2b.png" border="0" />
More random means more randomly distributed over the spread. 0 means equal distribution over the angles, 1 means completely random over the spread angle.
Of course you can also load instance variables instead of using local variables for spread, randomness and projectiles (not for a though).