Tuning Vintage HW70 trigger malfunction

[.20calguy]

Greetings

I have an HW70, from the early eighties. Some time back it jammed and wouldn’t cock. A problem I had forgotten about. I recently pulled it out and put a new piston, and breech, seal in it. While shooting, it jammed and wouldn’t cock! It cleared when I pulled the trigger a second time, which allowed it to cock. So this intermittent problem, let’s half of the trigger mechanism unlock, releasing the spring and firing, while needing the trigger pulled again to reset the sear for cocking. 
Any ideas on this issue?

Thanks

 

[.20calguy]

 

Here’s a look at the HW70’s problem.