If I recall correctly, after looking att the parts diagram in the down loadable pdf here:
h t t p://www.armscor.com.ph/img/pdf/M1600.pdf (copy and paste in browser, then remove spaces)
I believe my problem was with the pin in the rebound lever being slightly bent. I recall taking it out and straightening it out in a vise and it worked fine. You should also check to make sure that the screws holding the trigger housing to the receiver are tight. I ended up using JOB weld on my screw to hold it in place.