Hi Vic,
In Victoria, for most reef species, you generally won't be limited to what fish you can land with a shorter gun, but you will have a limited range.
That range along with the power of the gun will determine how close you need to be to a fish to punch through it with the spear.
If you want to minimize the chances of bending the spear on a big fish, wait for the fish to turn away from you a bit before taking the shot.
Make sure you have the speargun connected to a float-line and float, so if you do shoot something decent sized you minimize the chance of loosing your speargun.
Hope this helps
