[Bill McIntyre]

I find it hard to take this thread seriously, but I can't resist one comment.

Many spearguns don't shoot where they are aimed. A stock Riffe Island, for instance, shoots very low because the gun has insufficient mass for the weight of the shaft and the thickness of the bands that it uses. So it recoils, the gun rotates around the handle where the shooter is resisting the recoil, the muzzle rises and pushes the rear of the shaft upward, causing it to be low right out of the gun, even before the effect of gravity.

If the laser sight was aimed right down the axis of the gun, you would miss. I guess you could crank in some elevation in the sight, but how much for which range?