A recent email asked my help with a problem. The writer, who had purchased a new gun to compete in the IDPA revolver class, had taken the strain screw out of his S&W 686 and shortened it to reduce the trigger pull weight. When he put his grips back on, he found that the grip screw wouldn’t go through the frame, and he could see that the mainspring was now blocking the screw’s path.
He asked why this happened, and what could be done about the problem.
When the strain screw is shortened, the mainspring arch is changed. The strain screw is very close to the bottom of the spring, near the pivot point where the spring contacts the frame, and has tremendous leverage. Because of that leverage, small changes in the screw’s length make big changes in the amount of arch the spring exhibits. This in turn lowers the pull weight.
The problem is that the grip screws are all positioned on an assumption of the mainspring remaining in the stock position. As the arch of the spring is decreased, it moves toward the muzzle of the gun and ultimately intrudes on the path of the grip screw. This is why reduced rate mainsprings are produced by Wolff (and one or two others.) These springs are designed to have a reduced weight while maintaining a close-to-stock arch profile.
The solution to this problem is to get a reduced power mainspring and a new strain screw (which will need fitting to achieve the desired pull weight.)
Changing the function of any part in a mechanism can have undesired side effects, and it is best to proceed cautiously unless you know with certainty the outcome.
-=[ Grant ]=-
- Posted by Grant Cunningham
- On September 29, 2010