Finished the weapon. Put on dual Thera Tube Silver (about 60 kg = 132 lb draw per barrel).
Frightening. It send the 72 gramm missile about 10 cm = 4" into my new dense foam archery target.
Then I made an equally heavy short bolt from a wooden rod, and attached a spike. The effect is devastating. A flying ice pick.
Can't wait to see the effect on ballistic gelatin :)