Recoil spring wear, yes, it does happen.

[reconbob]

   Had a guy in the shop looking for a recoil spring and said he was stumped because he was

told that all coil springs never show wear, or something like that. So how was he to know if the

spring he got was new or not?

    Detecting wear of coil springs is fairly obvious if you know what to look for. Coils start to get

flattened and shiny. It's subtle, but it's there.

    The best way to check a Thompson recoil spring is to measure it. It should be 11 5/16" +/- 5/16".

If it's too short or loo long it should be replaced.

   Here is a photo of a new and worn Thompson recoil spring. The new spring is on the bottom. You

can see some of the coils on the used spring on top are starting to get flat spots and shiny.

 

Garand - the worn coils are in the middle

Browning Automatic Rifle - the worn/flattened coils are obvious

A coil spring is just about always going to be harder than the parts surrounding it. such as when paired

with a M1928A1 actuator which is not hardened. BUT, when paired with an M1/M1A1 bolt, the bolt is going to be

very nearly as hard as the spring and you will get wear. (Well, you always get wear, it's just a matter of how

long it takes.)

Bob

Edited March 4 by reconbob

[SP Sarge]

Goid info Bob. Nice post.

[reconbob]

       The guy saw my post and sent me a note - there is a guy on Gunbroker selling recoil springs

who says that "all springs never show any wear". OK. Perhaps we should not believe everything we

read on the internet...

Bob

[Doug Quaid]

"Spring set" occurs in addition to wear.

If a steel spring is under load for long enough, it will acquire a "set."   It will change dimensions and not exert the same amount of force for a given deformation.

This occurs to varying amounts.

When they make prestressed concrete bridge girders, they actually stretch the steel cables in the girder in order to create a compression force in the beam, to reduce cracking.   Over time, the cables loose about 25% of their initial force because they stretch.  

The technical name is "creep deformation."

"Creep deformation is a form of slow mechanical deformation that occurs when a material is exposed to high-stress levels for a long period of time. Creep is time-dependent."


 

[Maine-iac]

20 minutes ago, Doug Quaid said:

"Spring set" occurs in addition to wear.

If a steel spring is under load for long enough, it will acquire a "set."   It will change dimensions and not exert the same amount of force for a given deformation.



 

As I understand it, this isn't a factor for magazines and springs made with proper modern metallurgy and quality control. The spring "set" occurs once the load put on the spring exceeds a critical value, and has little to do with the duration of said compression. Case in point, there are plenty of folks who've tested the theory of spring set by shooting magazines that have been loaded for decades.

A far more common failure mode for springs is cycling strain accumulation.

[Outsider]

10 hours ago, reconbob said:

       The guy saw my post and sent me a note - there is a guy on Gunbroker selling recoil springs

who says that "all springs never show any wear". OK. Perhaps we should not believe everything we

read on the internet...

Bob

I saw that for sale post on GB just after readying your original post hear and just had to chuckle.

[Doug Quaid]

On 3/4/2024 at 6:59 PM, Maine-iac said:

As I understand it, this isn't a factor for magazines and springs made with proper modern metallurgy and quality control. The spring "set" occurs once the load put on the spring exceeds a critical value, and has little to do with the duration of said compression. Case in point, there are plenty of folks who've tested the theory of spring set by shooting magazines that have been loaded for decades.

A far more common failure mode for springs is cycling strain accumulation.

Steel has an "elastic limit", and once you go past it, you get permanent plastic deformation.

spring set or creep has nothing to do with plastic deformation, fatigue, steel purity, or manufacturing quality.

steel has a crystal structure, and the crystal lattice has billions of discontinuities in it.   when you put steel under load, you are storing energy in the material by stressing it.  

while it's sitting there for year after year with all that energy in it, the steel uses the energy to slowly reconfigure the discontinuities in the crystal lattice.  it's like it's flowing very slowly.    This is due to thermodynamics.  The material goes from a more ordered state to a less ordered state.

THE REASON THAT YOU DON'T HAVE ANY PROBLEMS WITH YOUR LOADED MAGAZINES IS BECAUSE THEY WERE DESIGNED TO ACCOUNT FOR THE 10% OR 15% LOSS IN SPRING STRENGTH.  

That's how you design around spring set - you either make the spring stronger than it needs to be, or you replace the spring every so often.  

Most of the time, spring set isn't a problem, but sometimes you'll have a gun that needs a fresh recoil spring or magazine spring in order to work good.

You know where you'd see a lot of spring creep?  In 1960s and 1970s Chryslers.  They used torsion bar suspension in the front and after 15 years, the torsion bar would run out of adjustment and need replacement. Nobody wanted to replace the bars on 15 or 20 year old car, so all the Chryslers driving around would have massive negative chamber that you could easily see.

[anjong-ni]

I remember reading a post from a fellow that had some identical  loaded-and unloaded 1911 magazines in his range bag.

They sat in a closet together unused for two years.

When he disassembled the mags and checked the mag-spring lengths for the article, the loaded ones had shrunk by 50%. ...Phil

[Rekraps]

On 3/4/2024 at 6:59 PM, Maine-iac said:

As I understand it, this isn't a factor for magazines and springs made with proper modern metallurgy and quality control. The spring "set" occurs once the load put on the spring exceeds a critical value, and has little to do with the duration of said compression. Case in point, there are plenty of folks who've tested the theory of spring set by shooting magazines that have been loaded for decades.

A far more common failure mode for springs is cycling strain accumulation.

I think you are right. As long as the spring is not compressed beyond whatever the critical point is, it will always retain its potential energy. 

[Merry Ploughboy]

According to one of the co-founders of Battlefield Las Vegas in a post he made on AR15.com a few years ago, for their rental M16s they buy standard, off the shelf recoil springs and get about 150,000 rounds with them before replacement when the spring gets too short.  Of course, the geometry on a Thompson spring is different as is the type of loading encountered.

[Doug Quaid]

There are two things that many, many men in the gun owning fraternity simply will never accept:

1. That you don't have to do all kinds of weird stuff to clean and/or stain and varnish a gunstock.  No matter how you want a gunstock to look, there is a product that you can buy to achieve exactly the results you want.  But, nope. 

2. That materials science is an incredibly sophisticated and heavily researched field of study.  In the world of some gun owners, materials science is considered to be the same as astrology, just a random set of mystical beliefs.

 

Edited March 10 by Doug Quaid

[Doug Quaid]

8 minutes ago, Merry Ploughboy said:

According to one of the co-founders of Battlefield Las Vegas in a post he made on AR15.com a few years ago, for their rental M16s they buy standard, off the shelf recoil springs and get about 150,000 rounds with them before replacement when the spring gets too short.  Of course, the geometry on a Thompson spring is different as is the type of loading encountered.

Spring creep increases with temperature, because heat is a form of energy.  And creep needs energy to happen.  

So how the gun is used is also a factor.  If they are heating the guns up by people doing back to back mag dumps all day, that could greatly accelerate the creep.

[damifino]

A quick search turned up this.

https://www.asraymond.com/blog/material-creep-what-is-it-and-how-to-prevent-it/

 

[Doug Quaid]

12 hours ago, damifino said:

A quick search turned up this.

https://www.asraymond.com/blog/material-creep-what-is-it-and-how-to-prevent-it/

 

If you keep looking, you'll find all kinds of massively complicated research being done on creep.

Structural engineers design for creep, but it's not a big deal, because you can just make parts bigger to reduce stress.   If you add 30% more metal, nobody cares.  Structural steel costs $2 per pound.   

But creep is actually a really big deal in mechanical engineering, because mechanical engineers design stuff that moves, and they struggle to keep the weight down.   So they do a ton of research on limit states like creep and fatigue.  So they can use lower factors of safety and make lighter designs.