Congratulations! You had the negligent discharge that every gun owner swears can't happen to them without killing something expensive or irreplaceable.

When workingwith mechanical or any other systems with tolerances, you need to use a bit of common sense. You can rightfully expect that if you turn screw 'X' that you shhould get 'Y' result, but in the real world it doesn't always work that way. Did you use a trigger guage to check the setting? A lot of triggers can only be safely set within a certain range.

I'm not trying to ride you hard or anything, but you might have just learned the difference between learning from a book and learning from experience- book learning is easy, experience requires pain.