That looks like something out of a sci-fi movie when it fires. I can't believe it takes you a full .2 seconds to hit. Have you tried using massive springs instead of speargun tubing? (Example:
http://www.mcmaster.com/#96485k272/=wzefsr although maybe something a little smaller)
When IRI is over, I would love to see the CAD for this. having a claw that auto-clamps on contact would be amazing for a lot of appliactions.