Originally Posted by Wee Hooker

What he said. Also, be sure to scrub the heck out of the cylinders . If the round sits out just a few thousandths, it can absorb energy of the hammer blow and cause FTF.

As for springs, it's not unheard of that a weak mainspring could be the cause. That is an easy and cheap swap. The trigger return / rebound spring has nothing to do with hammer force so it can be left alone. If you still have issues after cleaning and changing the mainspring, it needs professional care.