Should I rest the mainspring?

I've had my P938 for several years now and always leave it cocked and locked. I have not had any problems with the pistol when I do shoot it after leaving it cocked and locked all the time.

My understanding is that conventional wisdom regarding modern springs is they wear from use, not from remaining in one position. They do however 'take a set', which means they weaken slightly from their unused strength when installed and tensioned for a period of time. If they were made correctly and designed correctly for the application, this will result is them being correct for purpose once they have taken a set. And if Sig doesn't say the spring needs "resting", it surely doesn't.

But that might all be wrong. I'm not a spring engineer. So if you want to be sure it's okay, shoot it. If you're still concerned, replace the spring and test it. That should put your mind at ease.

I can't answer to the SIG 938, but the typical 1911 cocked and locked mainspring lifespan is often the life of the owner, if not the life of the gun.

Recoil springs and firing pin springs need regular replacement, and so do mag springs, but mainsprings almost never.

Facts: 1.-Just replaced a mainspring in a 70 year old FN Hi-Power, very similar to a 1911 mainspring. Original spring showed no signs of wear or weakness, despite being constantly cocked, in over 15 years, in which I owned it, or all the usage, in the 55 years previous to my acquiring it.
2. "Technically" speaking, springs (under the bald assumption these are reasonably good quality springs) don't wear out from being stationary, in either the extended or closed position. They wear from being used.

Ok, are you taking it out and shooting it with any regularity?
Even if only every couple months or so, you would see any sign of weakness in the mainspring.

However, it's highly unlikely. My Series 70 has had the hammer back for probably near thirty year with no sign of weakness.

I had that gun built in 1989. Carried it for 15 years. The only time the hammer was down was when it hit the firing pin to fire.

Sat with the hammer down until 4 years ago when it went back in service. Goes bang every time.

Steel used in springs today is so much better than the springs made in the late 1800s early 1900s.

But old habits, procedures, and wives tales die hard.

Good information about current manufactured springs already posted.

WrongHanded said:

My understanding is that conventional wisdom regarding modern springs is they wear from use, not from remaining in one position. They do however 'take a set', which means they weaken slightly from their unused strength when installed and tensioned for a period of time. If they were made correctly and designed correctly for the application, this will result is them being correct for purpose once they have taken a set. And if Sig doesn't say the spring needs "resting", it surely doesn't.

But that might all be wrong. I'm not a spring engineer. So if you want to be sure it's okay, shoot it. If you're still concerned, replace the spring and test it. That should put your mind at ease.

Click to expand...

Yes, expanding:

Properly built springs have an enormous life when properly used. Mainsprings are usually proper, in that the spring compresses (strokes) over a very small amount of it's total length.

Recoil springs and magazine springs are "improper" use, in that they are compressed solid; the stroke is a very high fraction of the total uncompressed length. That wears them out faster. Again, not by being compressed per se (not staying loaded), but by cycling a lot over this large stroke.

So, recoil springs, mag springs and usually others with the same issue (e.g. many extractor springs) need to be replaced regularly. Others with enough length to stroke ratio will outlast the frame. Since too few guns come with a spring replacement cycle chart, you can use this to tell which need periodic replacement and do it.



(Source: also not a spring engineer, but enough engineering background to follow the conversations, and I have had friends who were shooters and totally were engineers who did spring work every day, so investigated, and shared this stuff with me and others.)

LoneGoose said:

I don't need opinions; I'm looking for a technical answer based on fact.

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I’m sorry, I can’t help you out there. In my past life, I have worked with enough springs to know that they are a subject all their own. But resting a spring doesn’t even make sense. The key to springs is not over working. By that I mean not over extending compressing or flexing beyond their design limits.


Question:

If Sig says that your springs in your 938 need to be replaced at 5000 rounds. I have to believe that their engineering team believes that 5000 rounds would be about average. Personally my 238 (not the same, but similar design) starts eating itself up long before 5000 rounds. More like half of that. So, I keep a set of springs around. If I start to see a problem, I switch out the springs. Why, I guess I want my gun to work.


https://www.sigsauer.com/store/parts-kit-p938-9mm.html
https://www.sigsauer.com/store/recoil-spring-set-p938-9mm.html

Sig certainly doesn’t give their stuff away do they?

rskent said:

I’m sorry, I can’t help you out there. In my past life, I have worked with enough springs to know that they are a subject all their own. But resting a spring doesn’t even make sense. The key to springs is not over working. By that I mean not over extending compressing or flexing beyond their design limits.


Question:

If Sig says that your springs in your 938 need to be replaced at 5000 rounds. I have to believe that their engineering team believes that 5000 rounds would be about average. Personally my 238 (not the same, but similar design) starts eating itself up long before 5000 rounds. More like half of that. So, I keep a set of springs around. If I start to see a problem, I switch out the springs. Why, I guess I want my gun to work.


https://www.sigsauer.com/store/parts-kit-p938-9mm.html
https://www.sigsauer.com/store/recoil-spring-set-p938-9mm.html

Sig certainly doesn’t give their stuff away do they?

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Totally agree, 2500 rds at the most.(recoil springs) They wear down and that is a fact at least for the smaller guns. And I never leave Springs fully compressed, they wear down as well. The longer they are compressed the more they loose full function. Some might go bang, but I would not trust it.

I have heard the same arguments from Air Rifle enthusiast for decades. And these guys that shoot Springers, only buy the best High end springs. They did a study for over a year and published the results. Spring would start to loose full function in the first week. Over a year and they they would lose 50-60%. I had one gun Pocket gun that I tested and left loaded for one year. At the end the springs could barely push the rounds out. For myself, it is not worth a debate to carry on. I will not do it, most especially for my carry guns. I replace recoil springs and magazine springs on a regular basis.
Your gun, your life, do as you please. Just my two cents. Too much to risk to not do such a simple maintenance task.

2500 to 5000 cycles on springs seems pretty low.

2500-5000 cycles isn't that low for a recoil spring. Now if you have to replace a mainspring with that many rounds/cycles, something is wrong.

rskent said:

I’m sorry, I can’t help you out there. In my past life, I have worked with enough springs to know that they are a subject all their own. But resting a spring doesn’t even make sense. The key to springs is not over working. By that I mean not over extending compressing or flexing beyond their limits.

Click to expand...

Winner Winner Chicken Dinner! This is 100% correct. A compressed spring will not wear from being left in a compressed state assuming that the amount of compression is within its design and manufacturing spec. If the spring was design to be under X amount of pressure and Y length when compressed and under load in your gun with the hammer cocked it is under those specs you are fine. If however the spring it at or beyond it’s specifications then you will have spring wear. Same goes for mag springs. It is not the state of compression you have to worry about it is the amount of compression in relation to the spec if the spring. For most guns these days that spec is unknown.

The one caveat i can think of, is the rare instance. where some bean counter wants to save too much money,
and opts to put cheaper, inferior springs in a low quality firearm. But you won't see this, with most major brands.
Sig has a reputation to uphold.

Factory mainspring spring weight for a 1911 is 23# - I would replace it with a 25# that way after it "took a set" I hoped to still have close to 23#

CDW4ME said:

Factory mainspring spring weight for a 1911 is 23# - I would replace it with a 25# that way after it "took a set" I hoped to still have close to 23#

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The OP is asking about a Sig P938 so I am not sure that quoting the 1911 spec is relevant to this discussion.

My P938 has been cocked and locked almost constantly for the last year. No problems. It’s my understanding that use wears out springs so long as they aren’t over compressed.

WVsig said:

The OP is asking about a Sig P938 so I am not sure that quoting the 1911 spec is relevant to this discussion.

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Also, for rotating-hammer-fired guns, the hammer helps delay initial extraction. More spring can improve, OR can mess up the operation of the gun.

+ and -Power spring kits are often available for many guns by Wolff, etc. but I wouldn't change them without some idea why, and testing it for a bit before I assumed it worked properly.

I have seen plenty of recoil and firing pin springs weaken with age and cycling - but never a mainspring. I wouldn't worry about the mainspring.

WVsig said:

The OP is asking about a Sig P938 so I am not sure that quoting the 1911 spec is relevant to this discussion.

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Installing a spring a couple pounds heavier so that when it "takes a set" or loses some of its original force so it hopefully retains similar force to the "normal/original" factory weight is applicable beyond a 1911 - I used that example because I knew the weights. That specific example is not the OP's gun but the idea could be applicable; I did not think I would have to elaborate beyond what I posted initially for the connection to be made.

CDW4ME said:

Installing a spring a couple pounds heavier so that when it "takes a set" or loses some of its original force so it hopefully retains similar force to the "normal/original" factory weight is applicable beyond a 1911 - I used that example because I knew the weights. That specific example is not the OP's gun but the idea could be applicable; I did not think I would have to elaborate beyond what I posted initially for the connection to be made.

Click to expand...

Springs are suppose to be the correct weight after the Set. Look at high end Air Rifle Springs makers. They will tell you if you buy a new spring from them, that you need to do a :"Set". when you receive the New Spring. Or they will tell you that they the new spring has already Had a Set, and no need to do one.
For all my recoil springs and Magazines I do a Set. I load up mags to full capacity and let them Take a "Set" for 48 hrs.

CDW4ME said:

Installing a spring a couple pounds heavier so that when it "takes a set" or loses some of its original force so it hopefully retains similar force to the "normal/original" factory weight is applicable beyond a 1911 - I used that example because I knew the weights. That specific example is not the OP's gun but the idea could be applicable; I did not think I would have to elaborate beyond what I posted initially for the connection to be made.

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The problem with that advice with this particular pistol is that no one makes a heavier spring. IIRC the Sig P938 spring is a 20lb from the factory. People complain about it because it can yield an 8 lb trigger with that spring. So people look to use a reduced weight spring. There are again IIRC off the top of my head 18lb springs for P938s but that is going the wrong direction if you are worried about that spring getting weak over time. One could use a 23lb Colt Govt 380 spring from Wolf but the trigger would most likely suffer greatly. This is where generalizations fail when being applied to a specific.

People complain about the recoil spring weight on the P938 and it's impact on the trigger? I guess I got a good one.

Those people should try and original XDs-45. That's a heavily sprung gun.