Champion pics there bud
Right, just so you know what is going on in there when you pull the trigger, you see the little thing that sticks up at 45' on the top of the trigger group, that is your piston sear, this needs to move freely put also needs to be pushed up to the angle that its at fairly firmly so that when you cock the gun it snaps in under the piston and holds it back ready to fire. The long thing that its fitted in is the trigger sear, as you can probably work out, this bit applies pressure to the top of the trigger itself when the gun is cocked as soon as you pull the trigger it releases the trigger sear, which in turn brings the piston sear down thus releasing the piston.
There are 3 potential things that could cause your problem
The first, not as obvious as some might think, are you pulling the cocking handle as far back as the gun needs to cock? This might sound daft but how many people have you seen try to start a car that has obviously run out of fuel, but they have damn near stripped the engine to find the problem and all they needed to do was check the fuel gauge
Second, and most likely considering the age of your weapon, check the trigger adjustment screws. The little screws in front and behind the trigger 1 sets length of pull to release the other strength of pull. The length of pull can be set while you look through the little side window while you adjust the screw. The strength of pull is a matter of what feels good for you
Lastly, sear wear, the 45' sticky up, sprung loaded thingy on top of the trigger group
will have very obvious wear on the top leading edge. If it is obviously bad it will need replacing. Not a hard task considering you've quite competently got this far with stripping the trigger group
