Question on Wave Gun from More Thrust

How far out before it burst into a 2" diameter 4d6 traveling ball.  The
old 
Nova Cannon "cooks off" at 6" from end of the ship.  It doesn't says for
Wave 
Gun, and it came up in a pick up points game I played.	With 1 player
saying 
that the firing ship should be caught in the 4d6, if it comes out at the
2".  
Other saying the firing player ship is immune to the damage.

Have a Good One,

DOC Agren

     (Lurker on the Digest)