How long does a mainspring last? – Part 2

by B.B. Pelletier

When the mainspring starts to fail (bend), it rubs either against the inside of the piston or the outside of the spring guide on either end (inside the piston or at the other end of the compression chamber/spring cylinder). That rubbing slows the piston, causing a power loss, and it transmits vibration to the metal parts of the gun. If you know your gun very well, you can feel this increasing vibration, just as the owners of older Diana spring guns often notice the easier cocking and softer power stroke of a broken mainspring.

A few more factors
We still need to know a few more things. Some mainsprings are under a tremendous amount of pre-load. They are compressed 3-4″ while at rest! The HW77 is like that, as is the FWB 124. The TX200, on the other hand, is only compressed about half an inch at rest. That affects how long the springs last. So does dieseling.

The more a gun diesels, the shorter its spring life will be. Every diesel smacks the mainspring with a rapid compression stroke. There are cases where the gun has recocked itself from a detonation! That force abuses a mainspring something awful. As does a sloppy powerplant.

A gun that has a lot of slop between the piston, mainspring, spring guides and cylinder wall is abusive to a mainspring. When a spring gun fires, the spring expands and rebounds so fast that at one point it doesn’t touch either end of the gun! If there is lots of room all around, the spring will kink up in all sorts of nasty ways and get hit by other moving parts in the powerplant until it starts to degrade. A buzzing, vibrating spring gun is tearing itself to pieces, with the mainspring being the first victim.

So how LONG does a mainspring LAST?
Tom Gaylord published the only report I know about on the subject of mainspring life. In his R1 book, there is a chapter called the Mainspring Failure Test. He tested a factory R1 spring, a Beeman Laser spring, a Venom spring and a Maccari custom spring by cocking them all and leaving them cocked for ONE FULL MONTH! That’s 735 HOURS of being cocked. Throughout the test he took shots at intervals to see how the springs were holding up, then recocked them until the next test shot. Each spring was test-fired this way 23 times during the test.


The R1 book by Gaylord has a whole chapter devoted to mainspring life.

The mainspring that lost the most power was the Beeman Laser spring. After being cocked for 735 hours, it had 93.25 percent of the power it had at the start of the test. The factory spring retained 93.89 percent of its original power. The Maccari spring retained 94.65 percent of its original power and the Venom spring retained 96.93 percent of its original power. The Vemon spring was slightly bent and had begun to vibrate – something Gaylord stressed it did not do before the test. The factory spring was ever-so-slightly bent and both the Maccari and Laser springs were still perfectly straight.

How long?
A full MONTH of being cocked is more abuse than anyone can heap on a spring gun in ten years of normal use. However, (and this is a long list of “howevers”) a Chinese spring rifle MAY have an improperly stress-relieved mainspring that can fail in less than 1,000 shots. An older Diana from 1986 to 2000 will often have a broken mainspring from improper stress relief. That is not 100 percent guaranteed, however. An FWB 124 will often have a bent mainspring from failure due to excessive pre-load. An HW77 with a factory spring may fail after about 12-15 years of little or no shooting for the same reason. An older Russian spring rifle may fail due to the spring wire being too weak for the application. Any airgun that has been subjected to repeated dieseling will probably have a bent mainspring.

33 Responses to “How long does a mainspring last? – Part 2”

  • Anonymous Says:

    BB,

    does bent mainsprings also occur in automatic firearms? I have never heard of such problems but the cycling of a MG should be much harsher. Do they use different spring materials or is the tension much lower even with 50BMG?

    Markus

  • B.B. Pelletier Says:

    Markus,

    Indeed, fully automatic firearms bend operating springs like there’s no tomorrow! I remember the M60 machinegun being very bad for that. As I recall, the M2 was a lot more reliable, so its operating spring is probably not overly stressed.

    The M1 Garand bends its long, weak operating spring frequently. It’s one of the most common failures the rifle has.

    Like airguns, the rate of firearms spring bending depends on the design of the gun.

    B.B.

  • Fabian Says:

    Have you ever tested Mendoza refles? or seen their springs?
    They don’t have a good reputation even in the south side of the river, but I would like to hear your expert opinion.

    Regards,

    Fabian

  • B.B. Pelletier Says:

    Fabian,

    I haven’t tested them. This is due to time more than anything, though after hearing some of the same stories you mention, I’m not sure the Mendoza spring piston rifles will be around that much longer – at least not here in the U.S. I specifically refer to the model 2003.

    Mendoza has a good reputation as a firearms maker, so they can make airguns, too. It seems they have tried a price-point approach and it has backfired.

    Happens to the best of them.

    B.B.

  • Anonymous Says:

    Hi B.B

    I was in an antique store yesterday and came across a crossman A.I.R -17 .117 pellet/bb repeater, It looked like a colt AR-10.Personally I’ve never seen anything like it and I was wondering what information you had on it

    Thanks

  • B.B. Pelletier Says:

    The Crosman A.I.R. 17 looks like an M16. It’s a pneumatic. I had one and didn’t think much of it. Too much plastic, too little power and mediocre accuracy, as I recall.

    They do have a little collector value because they weren’t made long (1985-1990). NIB is worth $150. Average is $65.

    B.B.

  • Jed Says:

    Well I guess there is no safe way to boost spring break barrel rifles velocity.

  • Anonymous Says:

    I’m very sorry I’m answering so late computer problems. But you asked me Where I heard that Eun Jins were bad in 1250′s .22 was in gamos forums! alot of people say that they take out the breech seal and mess up tons of ther stuff, this air rifle is my pride and joy but I don’t have tons of money to be sending it in for repairs. I’ve learned not to beleive everthing I read but I was shocked to read this but if a springer prefers light to medium ammo do I toss my Eun Jins? will they mess up my main spring? There isn’t to much out there on this rifle (maybe I’m not looking right) but I hoped charlie da tuna would let me know if he could do any after market work on this model but no answer. In the end there’s alway’s the choice of sending it back to the factory. Like always sorry for posting off topic, and thanks for the help guy’s.

    1250 Robert

  • Anonymous Says:

    BB,
    I read your post on airgun power at altitudes. I was looking for information to see if an AEG airsoft gun would loose power at higher altitudes. I didn’t see anything listed in your altitude post concerning airsoft guns.

    How would an AEG change (if at all) at altitudes of 6000ft compared to sea level velocity? Thanks

  • B.B. Pelletier Says:

    Jed,

    There are ways to boost spring gun power safely. Many of them are in Tom Gaylord’s R1 book, which is out of print.

    B.B.

  • B.B. Pelletier Says:

    Robert,

    Usually I think everything in the forums is crap, but this sounds right!

    The Eun Jin is a fat pellet, as well as way too heavy for a gun like the 1250. It has a lot of resistance in the bore. I’m used to shooting it in a Condor with no problems, but a 1250 has less than half the energy. So, if they say it blows breech seals, I’d listen.

    B.B.

  • B.B. Pelletier Says:

    An AEG is a spring-piston gun with the piston driven by a motor. It will be affected by altitude just like any other pioston airgun.

    B.B.

  • Anonymous Says:

    Thanks B.B.

    Robert

  • Anonymous Says:

    Does that mean you can only shoot the eun jins with the condor cranked all the way or will they work in the SS in .22cal?

    Robert

  • B.B. Pelletier Says:

    Robert,.

    Kodiaks are about the limit for the SS unless you install the 24-inch barrel. Then the SS will shoot Eun Jins well.

    B.B.

  • Anonymous Says:

    If Mendozas are no longer imported, perhaps they will become collectible?

  • B.B. Pelletier Says:

    If you wait long enough, anything is collectible. Mendozas were highly sought after before they made their American debut. Once shooters saw the relative lack of quality, however, the word spread fast.

    B.B.

  • Anonymous Says:

    i hav a air17 air rifle it is over ten years old it dosent shoot any ideas

  • B.B. Pelletier Says:

    AIR17,

    Yes, Drop about five drops of motor oil on the pump head and see what that does. With the gun on its back and the pump handle extended, the pump head is just visible at the end of the pump slot.

    B.B.

  • Anonymous Says:

    I got a bargian on an AIR 17 only ahundred bucks, when you said the accuraccy was bad, you were wrong, I hit flies with it.

  • B.B. Pelletier Says:

    AIR 17,

    That’s great! I assume you shot pellets to do that?

    B.B.

  • Jake Says:

    Hi, I have a old crosman 3100. It doesn’t have much power. I think i need a new spring. Where can i buy one? How much is it worth?

  • B.B. Pelletier Says:

    The 3100 is a Spanish breakbarrel Crosman sold in the late ’80s.

    Try John Groenewold for parts:

    John Groenewold, PO Box 830, Mundelein, IL 60060-0830, (847) 566-2365

    B.B.

  • wb6csh7 Says:

    Hello B.B.,
    I always seem to come back to your blog and PyramidAir.com website when I run into spinger problems! Must be that you freely give of yourself and your time to those with “elememtary questions”!

    My “problem” is the Gamo 440 combo in 0.177 that I purchased new about 6 months ago. It seems to be very INaccurate, and the discharge sound of the rifle has changed over the past couple of months. Is their a wood penetration test I can perform to Rule Out the broken mainspring? I was trying to avoid going to the not-so-local shooting range for a chrono test. The 25.8 yard 5-shot groupings were as follows:
    Daisy Match Grade = 1.5″
    Gamo Hunter = 1.75″
    Gamo Magnum = 4-3/8″

    Bench rest was a sturdy wood chair with a (sleeping) pillow supporting the rifle above the chair’s seat. Wind was calm, T=81F, altitude = 4,000 feet. A 4X32mm BSA scope was used to align the printed targets.
    Previous to this – several months ago – the Daisy Match ammo produced groups of slightly less than 7/8″ at 25 yards. The other pellets (Gamo Hunter, Gamo MasterPoint, Gamo Magnum, and Crosman Copperhead) always produced unacceptable groups (2″+). One other pellet than did fair (~1″) was the Gamo Match. That was before the different sound started!

    So, can I expect complete and consistent penetration of a 3/4″ pine board as a preliminary test?

    Any helpful hints will be appreciated!

    Michael

  • B.B. Pelletier Says:

    Michael,

    First, let’s get some pellets that are of known accuracy. JSB Exacts are good, as are Crosman Premiers. You didn’t mention the caliber but I’m guessing a .177, so get the 7.9-grain Premiers.

    Second, have you cleaned the barrel? It sounds like you are leaded up and should clean with JB Bore Paste. Read this:

    http://www.pyramydair.com/blog/2005/11/is-your-airgun-barrel-really-clean.html

    As for penetrating the pine, sice wood can vary greatly in hardness, even in the same board, I would rather use ballistic putty. (duct seal). Look for a one-inch penetration.

    At 25 yards with a good 440 you should get 3/4″ groups when using good pellets. If you are getting 3/4″ penetration in wood, you are doing fine.

    The sound of a rifle can also change as it breaks in. Don’t rule that out.

    B.B.

  • andreas Says:

    BB

    When someone hunts with a spring airgun, does he cock and wait for game to appear while being loaded?

    I am somewhat worried to do this and also when I plink, I keep having the thought that I have to shoot within a few seconds of the cocking.

    Thanks

  • B.B. Pelletier Says:

    andreas,

    When I hun I do not have the rifle cocked or loaded. That’s why spring guns are difficult to hunt with.

    The mainspring failure test proved that you can leave the spring cocked for hours, but after 1000 shots of that you will have worn the spring out.

    B.B.

  • Rick Says:

    BB
    My rws 460 was left cocked all night;something like 20 hours. will that affect the power greatly?

  • B.B. Pelletier Says:

    Rick,

    20 hours isn’t too bad. They start loosing power around 100 hours.

    B.B.

  • Rick Says:

    Thanks
    Im relieved. im going to find your book so that i can read more on main springs and about my R1. Do you know who sells a copy?

  • B.B. Pelletier Says:

    Rick,

    No one sells it! It’s out of print. Used copies go for up to $80 on Ebay.

    That’s why these last four copies are such a treasure.

    Try asking here today:

    http://www.airgunwriter.com/

    B.B.

  • Anonymous Says:

    To decharge a spring rifle without a pellet in it, could this harm the mainspring?

  • B.B. Pelletier Says:

    A dry-fire (what you describe) is more damaging to the piston seal.

    B.B.

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