Installing the hammer spring backwards or forgetting to put the cotter pin back in the BCG makes for a fun day at the range!
I’ve done the backwards hammer spring thing twice. You’d think I would have learned after the first time.
First time it was almost all light strikes. Second time
I got 2 light strikes in about 100 rounds and I only noticed it because I took it apart after the hammer pin was starting to walk (when I got the light strikes was that range session right before it backed out).