First, I want to say that I just recently found this forum and I think it's great. There is a lot of great info shared here.
I bought a used complete trigger group lately that has a problem I've never had with a 10/22. It seems that it has all factory parts, and someone has tried to do a trigger job. I first thought it was OK. The pull is about 2 1/2 lbs., and it is very smooth with almost no creep. The trigger group passes all the safety tests I could think of, and all that are mentioned here. I did not notice the problem until I put it in a receiver and test fired it.
If you hold the trigger down when you fire the gun, the sear catches the hammer fine, but when you release the trigger it fires again. (Not a fun surprise the first time!) If you pull and release the trigger with no delay it functions perfectly.
The hammer and sear both appear to have been stoned, so I've already got a replacement hammer and sear, but I was just curious if anyone else had ever had a trigger group do this, and can you explain how it does this. If I replace the sear only, it fixes the problem and raises the pull to about 3 1/2 lbs.