Lair posted already as it has a bit more relevance there-- but thought it may interest a few here also--
Ok-- its been a while-- and this isnt the one that I started working on, but I got sidetracked to see it I could get a single stage one working-- Here is the ROUGH and I mean ROUGH design-- Nothing is attached or fixed-- Im basically just holding stuff together to demo how it will work.
The other one I am working on is a double action one-- both sides work. This one is just one side-- for now!!
Working Spear in process - YouTube