dahermit said:
...the strengths of the main and return springs are designed to be balanced, since they work in concert.
Can you explain exactly how they are designed to work in concert and what would happen if they did not?
The mainspring tensions the hammer, whereas the rebound spring tensions the trigger. Upon trigger return, the trigger physically resets the hammer, so it has to work against mainspring tension. Because double action moves the hammer and trigger, the DA pull is a function of main and rebound spring tensions. In contrast, single action just moves the trigger back to break the shot, so the SA pull is mainly a function of the rebound tension.
The main and rebound springs should be balanced. A stock DA revolver has a DA:SA pull ratio of about 2.5 - 2.7, and it seems to me a good reference when swapping springs.
If the main is relatively heavy compared to the rebound (or, said another way, the rebound is relatively light), the trigger will be sluggish resetting (in extreme cases, the trigger will inconsistently return to it's fully forward reset position). Shooters who shoot DA and ride the trigger on the return (a very common habit that most wheelgunners don't realize they do) will find themselves short-stroking the gun. Shooters who shoot SA will find they've got a very light SA trigger.
If the main is relatively weak compared to the rebound, you'll have a DA pull weight that's heavier than it needs to be for the reliability you've got. The whole point of running "Federal-only" loads, for instance, is to significantly reduce DA pull weight.
Driftwood Johnson said:
In this photo I have backed the strain screw out too far. I am encountering resistance to the hammer going back all the way to full cock. What is happening is the new curve the spring took is forcing the stirrup to pivot too far.
Interesting. Good to know.
Driftwood Johnson said:
Competition shooters have known for many years that they can lighten the double action trigger pull by grinding the rebound slide spring shorter.
IME, competitive wheelgunners (IDPA, USPSA, ICORE) lighten the double action by adjusting
both springs (and as part of a good action job) for the reasons articulated above.