Sent you a pm. If you remove the mainspring and then try it and it works, then the chances are that the front of the sear is worn and will need replacing. You may be able to file the angle of the sear forwards from the bottom of its hole to square it up so the angle is less \ and more L. It could be the piston worn where the sear engages but unlikely. Ive had this problem with small Diana,s that held ok until a new spring was fitted and had to file the sear. Also I have a paratrooper with a different trigger set up that was doing the same thing so I filed the sear and took 2 coils off the mainspring to give the sear an easier life. I hope this helps.