The flat leaf mainsprings in all S&W revolvers except J-frames are, for practical purposes, a fitted part. Actually, it is the strain screws, not the springs, that are fitted. But the result is the same. The leaf mainsprings cannot just be swapped between frames with consistent or usable results. The strain screw needs to be the correct length to provide the correct tension. Depending on the frame, the spring, and the screw, things may work out nicely, or you may need a screw that is longer or shorter. If you need a screw that is longer, then you will need a new screw.
None of the spring kit vendors are clear about fitting the strain screw. I think this is unfortunate, but there is a viewpoint that if you don't already know all about this, then you are not really prepared to swap springs.
I have had good results with Wolff reduced power springs, but you very typically need a longer screw. Some people prefer the Wilson kits because they more often, but not always, work with the existing screw. I have not used the Miculek springs, but he is very clear that they are designed for competition guns using Federal primers only.
Some years ago, I wrote a long article about working with the triggers on S&W revolvers. The article is much longer than most people want to read, but it is not difficult, and most of the info will be helpful to anyone who wants to work inside revolvers.
Table of Contents 1. Part One: General Concepts 1.1. Introduction 1.1.1. Disclaimer 1.1.2. The author is not compensated for endors...
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