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Education / Training How long does a mainspring last? – Part 1

How long does a mainspring last? – Part 1

by B.B. Pelletier

Here’s a question all spring gun owners have asked. We got this question from an anonymous reader last week, but I know it’s one many of you will be interested in. This will take some time to explain, so please bear with me.

What happens when a mainspring fails?
Before answering how long a spring lasts, we first have to know what a failed spring looks like. Mainsprings fail in several ways, and for a couple of reasons. The most common failure is when the steel in the spring relaxes, allowing the steel structure to shift. I will come back to this later, but for now, let’s learn what happens when a coiled mainspring is made.

Turning a wire into a spring
I’m not going to explain steel structure, but think of a spring as a straight rod that has been twisted into a coil – because that is exactly what a coiled steel mainspring is! This rod is actually a thick wire, and that’s important to know. When wire is made, the steel structure aligns itself along the linear axis of the wire and is then twisted into a long coil. The steel structure is stressed in the same way a tree is stressed when it is bent over to one side. There are ways to relieve the stress in the steel, but let’s first consider where that stress is located.

Mr. Wizard time!
If you’ve ever served in the military or played in a marching band, you know that when a column of marching people turns a corner, the people on the outside have to move faster than the people on the inside. So it is for a steel wire being twisted repeatedly in a circle. The steel on the outside of the wire tries to move more than the steel on the inside of the wire. Except that the outside of the wire wraps COMPLETELY around the wire, while the marchers are a flat ribbon, by comparison!

The shaded portion of the wire has been work-hardened during the winding process and is very brittle.

Stress relief
If the stress is left in the wire, the surface remains brittle and subject to cracking. Further stressing, through spring compression and decompression, will cause the spring to fracture like glass! The most common way to relieve the stress is to massage it out with the impact of millions of tiny balls – commonly called shot-peening. A spring that has been shot-peened has a microscopically rough surface that looks like millions of tiny craters around the entire surface of the wire.

Close examination of the break point of a mainspring reveals a stattered structure, typical of an over-stressed steel that was not properly stress-relieved. The shading seen in the steel is real – not caused by shadows.

A well-made mainspring
When a mainspring is made right – with the proper steel, the correct manufacture and the proper stress-relief treatment, it doesn’t shatter like glass. But it does fail! However, the time it takes to fail is orders of magnitude longer than the bad mainspring, so it is considered acceptable for that application. When a properly made mainspring fails, the steel structure around the circumference of the wire shifts, allowing the spring to bend at that point. The bent spring then puts uneven pressure on the inside walls of the powerplant when it decompresses and that results in vibration. The more vibration a gun has, the more you can determine something is wrong inside – often a bent mainspring.

This old mainspring served an honorable life in a military trainer, which means tens of thousands to hundreds of thousands of shots. Even if it is a replacement, it still shows lots of service. The coils are bent AND collapsed.

Tomorrow I’ll pick up at this point.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

12 thoughts on “How long does a mainspring last? – Part 1”

  1. I was wondering where I could get replacement springs my son has a Daisy 102 that has a lot of sentimental value to him. It belonged to his biological father before he died. He would like it working again, I know it’s not economical to repair it but that’s not the point. Any help you can give me would be appreciated. I live in Ontario but visit Northern New York often. If you know any good airgun shops in this area it would help.


  2. I am amazed at the durability of some “springers”. My Walther LP53 has 44 years and thousands of shots on it and it still performs close to new. I bet you can’t say this about co2 and Pumpers that have not been resealed.



  3. I bought a used f/x pump w.o. instructions and proceeded to remove the black grease from the pump shaft and replace it with a standard bearing type grease is this something i shoud have done? If the black grease is special and i need to get some where could it be purchased thanks Dan

  4. Hi there,
    i have a bit of a problem. i have a marksman repeater 1010 and just recently had to replace an internal part. but when opened the pressure of the main spring caused all the little parts to fling out.
    i have been wrecking my brain trying to figure out where a small L shaped spring goes. i can see that the trigger, safety latch, and release button all need a form of spring loaded action. it looks as though the all work off eachother, but i still cant see any possible way to fit the spring.
    if you could help me out in any way at all it would be much apreciated.
    thanks for your time.

  5. I know, but another problem I have is that I am in australia.. so anything to do with bb guns are a rarity. If I had access to half of the things youse can get I would not be bothering with a 1010. as I dont know anyone who can send me anything else.
    Its a shame there is no diagram or exploded view of its assembly.

    Thankyou again

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