I managed to sneak a few minutes in the garage away from making mince pies and sausage rolls to get the sliding rails done for the trigger mechanism. It's pretty smooth! Mind I did wipe it over with beeswax polish first as aluminium can be a bit of a poor sliding surface.
I'd been pondering how to do it for some time, then I remembered some aluminium angle that I'd been given a while back. I knew it would come in handy.
Just about ready for testing, just got to work out a peg arrangement to trip the trigger and some way of pulling it back along the track. Got to be aware of the recoil when it looses, don't want it hurtling back and whacking the operator!
Another minor problem is the balance. The main horizontal arm that has the bow on one end and the trigger mechanism on t'other is a bit back heavy. I can move the pivot point a few inches, but I'll probably give it a try out first.
It'll all be over by Christmas!