If this happened with a 4006 I helped maintain, and it had just received a detailed disassembly, I'd start by carefully checking to make sure the gun was assembled properly. It's easier than you might think to make a mistake during reassembly, especially some less obvious mistakes. (For example, it's not difficult to miss having the rear of the drawbar plunger properly seated and captured within the circular indentation in the front of the drawbar's head.)
If everything was assembled properly and I eliminated the sear spring being damaged I'd suspect either the hammer and/or sear being involved. The easiest thing to check would be to simply drop in a new hammer and sear. I'd perform the normal bench checks to make sure the new parts provided for proper function in that gun. If the gun worked properly during the bench checks I'd take the gun out to the firing line to confirm normal function during live-fire.
If everything was assembled properly and I eliminated the sear spring being damaged I'd suspect either the hammer and/or sear being involved. The easiest thing to check would be to simply drop in a new hammer and sear. I'd perform the normal bench checks to make sure the new parts provided for proper function in that gun. If the gun worked properly during the bench checks I'd take the gun out to the firing line to confirm normal function during live-fire.
