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Main spring effect on trigger pull, P-series

This is a discussion on Main spring effect on trigger pull, P-series within the SIG Sauer Gunsmithing forums, part of the SIG Sauer Forum category; I originally posted this on another forum a couple of months ago. I've learned some additional info since, corrections are preceded and followed by **. ...


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Old 01-10-2016, 10:37 PM   #1
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Main spring effect on trigger pull, P-series

I originally posted this on another forum a couple of months ago. I've learned some additional info since, corrections are preceded and followed by **.

Hammer or main spring strength, as we know, has a direct affect on trigger pull weight (nothing new there :c). With double action, or modifications of DA such as DAK, LEM etc, where the trigger is directly compressing the hammer spring for at least part of the cocking main spring compression, the spring strength's affect on trigger pull is significant. It's a mechanical thing, work (pulling the trigger) is being done through some manner of linkage and lever to compress the mainspring. In my tests below you can see this direct effect.

On the other hand, with SA the slide is doing the work of cocking the hammer fully, so the hammer spring strength affects trigger pull weight in a more indirect manner, mostly due to increased tension at the sear to hammer interface, as the sear blocks hammer "rotation" until the sear is released by pulling the trigger. Thus the effect of varying mainspring strength on SA trigger pull should be less. **I've seen a trigger pull reduction of up to 5 lbs after properly fitting a poorly fitted sear to hammer interface. This on a P938 that somehow escaped Sig factory with a trigger pull of over 12.5 lbs. I should note too, that a sear with a more positive angle cut will tent to exacerbate the ramp up of trigger pull to spring strength in SA, as it must slightly further cock the hammer and compress the main spring as the sear "cams" out of the hammer notch to release the hammer.**

So, to find out more, I did some testing with springs from Wolf and Gray Guns (GGI). ** Gray Guns told me thay purchase there main springs from Wolf, so the variations I observed are batch to batch variations in manufacturing. i.e. a spring may be labeled as 17 lbs, but the actual spring strength may vary a bit. In my tests, GGI means Wolf springs too - different batch.**

The test gun is a '99 vintage P229 DA/SA. I had previously done a trigger job on this gun, polishing internals and fitting sear to hammer. All trigger pull measurements listed are averages of 10 pulls each, all done in the same manner, holding gun stationary and pulling from mid point on the trigger, parallel and in line with slide, slowly increasing tension to break using a calibrated Lyman digital scale.

Prior to testing, I measured the installed length of a hammer spring on the test pistol, both "relaxed" and at full cock. The spring length at full cock measured 0.850".

I cobbled together a digital spring test stand using a SS draw rod. I made a hook on one end and threaded the other for a washer and nut to capture the spring. I passed the draw rod through a Delrin bench block held in a vise. And then used a digital scale (not the Lyman as it overloads at 12.5 lb) to pull the draw rod to compress the spring under test to the aforementioned 0.850" length. All three Wolf springs were close to their advertised strengths of 17, 18, and 19 pounds when compressed to a length of 0.850" (they were all about 3 or 4 ounces under their rated strength. They doubtless use a proper test rig - - so I'll call mine a little bit inaccurate - - but at least it seemed to be consistent.)

I only tested two samples of GGI's 17 lb springs **Same as Wolf, I'm guessing different batch**. Both of these springs measured just under 16 lbs on my test rig, a full pound under the Wolf 17 lb springs (this difference is also born out in the trigger pull numbers to follow).

Hammer springs were swapped out and both DA and SA trigger measurements made, no other changes were made to the test gun between spring swaps.

Wolf springs:

17 lb spring / DA 8 lb-11 oz / SA 3 lb-14.3 oz

18 lb spring / DA 9 lb- 1 oz / SA 4 lb- 2.6 oz

19 lb spring / DA 10 lb-.5 oz / SA 4 lb- 5.1 oz

(Note: you can see the trigger pull weight moving up in a non-linear fashion, with a much bigger jump from 18 to 19 than from 17 to 18 - no conclusion here, but I wonder if testing a 20 lb spring would have more dramatically increased trigger pull?)

GGI spring:

17 lb spring (measured as 16 lb.) / DA 8 lb-7 oz / SA 3 lb-13.5 oz

(Note: if you consider the GGI spring as 16 lb spring and plug it's numbers in ahead of the 17 lb Wolf, the even smaller step in trigger pull weights lends additional credence to the idea that DA trigger pull weight increases non-linearly and faster as hammer spring strength increases.)

I did one final "test" to confirm the Wolf and GGI 17 pound springs really were of different strengths. Using a Delrin plastic punch dropped down the barrel, I shot the rod out of the barrel with just the firing pin impact on the rod. The GGI 17 lb spring shot the rod approximately 3 feet high while the 17 lb Wolf spring shot the rod 8 to 12 inches higher in a half dozen tests each.

Please note that I am not saying GGI springs are of lesser quality than Wolf, or visa versa. I have no idea how they each "rate" their spring strength. I used a compressed length of 0.850" as that is what the spring measure on the gun AND that happened to be the length of compression that the Wolf springs were close to their rated weight.

After the tests, I installed an 18 lb Wolf spring in the gun.

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Last edited by bumper; 07-03-2016 at 07:12 AM.
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Old 01-16-2016, 03:13 AM   #2
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Why the 18 and not the 17?

Great post by the way!
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Old 01-16-2016, 03:41 AM   #3
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I'm sitting here early on a Saturday morning fondling my new P226 Legion thinking to myself, "How can I reduce the DA pull weight on this thing?" I mean, it is powerful enough to catapult rocks to the moon, I think.

Ten pounds...yowzers. I guess I'm a bit spoiled at this point by my Wilson Combat Beretta Brigadier Tactical, which has a reduced power mainspring (the D hammer spring).

And up pops your article, brother.

Wow, talk about a home run with a first post!

.

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Old 01-16-2016, 03:42 AM   #4
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BIG QUESTION TO/FOR ANYONE WHO HAS SWAPPED OUT THE MAINSPRING:

Have you experienced any light primer strike/fail to fire issues as a result?

.

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Old 01-16-2016, 10:00 PM   #5
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Quote:
Originally Posted by fishpick View Post
Why the 18 and not the 17?

Great post by the way!
Good question. I guess 'cause I'm a bit of a coward. 17 works, I tried it, no miss-fires, but the primer impression is a tadge shallower than with the 18. And I think Gray Guns recommends no weaker than 18 for carry, 17 for competition. That colored my decision making I guess.

I'm working on a new to me (and almost brand new) P226 SS Elite made in 2010. Going in it has a DA of 11.5 lbs and a SA pull of just over 5 lbs. Nothing like my P229 carry with smooth DA of just over 8 and SA 3.5. This P226 has all kinds of stiff and stagy stuff going on during the DA pull. I'll report back on how it turns out.
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Old 01-17-2016, 04:56 AM   #6
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Quote:
Originally Posted by Amsdorf View Post
BIG QUESTION TO/FOR ANYONE WHO HAS SWAPPED OUT THE MAINSPRING:

Have you experienced any light primer strike/fail to fire issues as a result?

.
Yes, but only with a 16 pound mainspring that was brand "X" and was over 18 months old. I don't remember where it came from.

Going to 18 or 19 solves the problem nicely but increases the trigger pull on my 220 DAO.
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