It also sounds like the sear is not catching the hammer lug. You may want to set it with the gun de-gassed first.
To check it, de-gas the gun and manualy pull on the back block without pulling on the trigger. Push it back forward and close the breach. If you now pull the trigger the hammer should go forwasrd and hit the valve. If nothing happens when you pull the trigger then the hammer didnt catch the sear. Lower the hammer lug with an 1/8" hex key.
Good luck. It looks promising.