It's my own fault, I know. I trusted a friend's self-proclaimed expertise to do a "trigger job" on my S&W M&P 15 lower. I now get intermittent 2-round bursts. Looks like the hammer and disconnector got too close to the file and need replaced. Should that do it, or have any of you had to go further and replace springs, pins, or other widgets? I know it ain't fixed 'til it's fixed, but any words of advice or other things to look for? Thanks in advance.