Quote:
Originally Posted by rraisley
While I haven't been following ALL of this, I think you're missing something. Yes, cutting a spring down increases its spring rate. In a car, that works out great, because you get increased spring rate AND a lower ride height. But most springs used in firearms don't work that way. We can't change the "ride height".
Using your example above, of a spring with 10 #/" spring rate compressed 3", and cutting 20% (3 of the 15 coils) off, I don't think you will see an increased in installed force, either before it is compressed or after. Let's say the free length of that spring is 4", and it's compressed 3" in normal use. So, it's total length goes from 4" (free) to 1" (compressed). We'll assume here it doesn't go solid.
Now, if you cut off 3 coils, or 20%, ignoring end treatment, you will be shortening the spring by 20%. It will now be 3.2" long, free length. It's spring constant, as you say, will be 12.5 #/". BUT - it will no longer be compressed 3". If it's placed in the same mounting as the previous spring, it will be compressed until it is the same compressed length as before: 1". Which means it's now being compressed only 2.2", not 3". And the total force to compress it will be 2.2 x 12.5 = 27.5#, not 30#. Partial compression, say where it was 1.5" compressed before, will be even worse: whereas the 4" spring was compressed to 2.5" under those conditions, the cut spring will also be 2.5" long, being compressed only 0.7". So at a 2.5" length, the uncut spring had a force on it of 1.5 x 10 = 15#, while the cut spring has a force of 0.7 x 12.5 = 8.75#.
A simple way of looking at it is if the 4", 10#/" spring was cut to be only 1" long, it would not be compressed at all to fit in the 1" area, and while its spring constant would indeed by 40 #/1", it would provide no force at all in this example.
Am I missing something?
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You were not paying attention to what I was using as an example. With the original example I was showing a captured length that was 3 inches less than the free length. After cutting the spring the free length is less so the amount of compression preload will be a shorter multiple and my example was based on a theoretical spring so when I cut 3 coils off and remounted it the compression preload of a shortened spring would be a lower multiple than the original 3 inches. I was using 2.75" as the amount of compression length to fit in the same captured space. Of course that varies by the dimensions of the parts and the space.
The example was based on showing that regardless of the amount of cutting (as long as the spring still needs to be compressed to fit) while the preload may be lower, once the spring is compressed in action the spring rate will go up past the original as some point in it travel.
I'm pointing out that if you want the spring to hit harder you have 2 choices. Increase the rate of the hammer spring so it hits the FP harder or lessen the rate of the FP spring. And to do that correctly you need to choose a new spring with the same free length but a smaller diameter wire, to lessen the spring rate. And that was so you keep the springs rate of change the same. Anything else is hit or miss. Basic rule is if you cut off 10% of the active coils you will get a change in rate of around 10% (slightly higher actually but not significant). Cutting 20% actually changes the rate by around 21%. This is why when you want to correctly change the recoil spring in your pistol you get a new spring with a different rate, you don't cut the old one, because you need to keep the free length the same. In a car the issue is that cutting the springs will lower the spring bind point to below the bump stop height. So you need a lower, stiffer bump stop in that case.
This is one reason JP sells a spring kit that has the Yellow trigger spring but the Red hammer spring. If I was having light strike issues I would have left the factory hammer spring in and just put in the JP yellow trigger spring. I have considered that for my S3G trigger since it appeared to work fine with both yellow springs in ,but I went back to the Geissele springs to get the pull back up into the 2.5# range. Maybe later this year I will try it with the yellow trigger spring in and see what the trigger characteristics are.