Think it's about time for an update!
So the break barrel was put on hold for a bit. The first prototype (up to about 10 ft-lb) finally let go and made a mess of its cocking linkage (due to a design oversight on my part!) And at the same time we had a baby so life changed a bit!

However in the last couple of weeks there has been some progress. A new cocking linkage has been designed which should be far superior to the first one. Parts for that are in production now and should be 3 weeks or so before I get them.
In the meantime I need to sort out a stock. I reckon you need all the leverage a stock provides to really test the limits of the cocking linkages.
Unfortunately my 'prototype stock' fund has just been wiped out by an unexpected car bill

So I've had a dig around and found my old TX200 frankenstock. With some modifications I think I can get the prototype to fit. Then do some major reshaping to get it looking sensible.

I've also re-worked the piston (in CAD only at this point) which brings the dynamic mass from 400g down to roughly 280g. This should really help give the spring an easier time and give an efficiency boost (400g was just too much to accelerate properly).