This is a actually a followup question to my post on Cleaning a SW 639. After cleaning I noticed the trigger pull was pretty heavy. I understand that SW placed a 22 lb hammer spring in the original gun. I purchased a Wolf spring set and replaced the original with a 16 lb which really smoothed out the trigger pull.

I have seen several discussions about also replacing the trigger return spring to make the action even smoother. I found one article indicating the original was 4 lb.

Just what effect does changing the return spring have? Does this mean the trigger will not return back as far or does it impact the striking of the firing pin or both or something else?

It's simply the spring pushing the trigger back. As you've found out it's not much, 4-4.5# from the factory. You can lighten it up some, maybe 3.5# but you're not making a whole lot of difference, too light and the trigger isn't going to reset very fast which can slow follow up shots.

Thank you handgunner. I wanted to make sure before taking the trigger apart. I think I will just leave the original in place. I was pleased with its performance at the range.