Managed to get a few hours on the break barrel today.
New cocking linkage is working well. Maybe 200 shots in total today and no real issues. Got a bit of metal to metal contact during cocking, will investigate that tomorrow.

Was playing around with single piston (recoiling mode) and efficiency is now up to 31% with a 10 inch .177 barrel. Still a bit more to do but it's getting there.
Added the recoilless piston back in but by this time I was being summoned back indoors. Had a couple of shots and it felt goooood. The tiniest little movement, but the weights still aren't balanced.
Will try to get back out tonight to chrono in recoilless mode.

Motivation has been boosted by those couple of (almost) recoilless shots.