See misfires in the FAQs sticky, there are at least three links on them.
Tim
Tim's right, he has spent countless hours linking threads for all of us to find the info we need!
Long story short...
WEAK springs are a known issue... Short firing pin protrusion is another... Weak springs are exacerbated with hammer extensions..
I recommend you check pin, should be at least .040" then buy and install a Wolff spring.
Good luck,
CW