Dbarn,
Loss of mass on the hammer if combined with a light hammer spring will affect reliability. As long as the hammer spring remains constant, usually there is no issue. Had a problem with a SIG back in the day and I changed both at one time. Then spent months trying to figure out my issue. Once I reinstalled the original spring everything was fine and was able to drop it a couple of lbs., but not 5, which is what I originally did.
JW