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BB’s ‘speriment: Part 1

This report covers:

  • NotRocketSurgery
  • A coiled steel mainspring CANNOT be compressed farther than coil bound!
  • Where the mainspring lives
  • Removing vibration from a spring-piston airgun
  • But wait…
  • Some more on mainsprings
  • One final thought
  • Summary

I have wanted to write this report for over a month. I have been quiet too long about what I believe is a major error that’s been allowed to stand without opposition. GunFun1 — today I’m picking on you. But not to worry — you come out the winner in the end.

NotRocketSurgery

Oh, and reader Not Rocket Surgery, in March of 2012, you asked me a question I said I couldn’t answer.

“Gents…

Once a spring has been scragged is there any reduction in cocking effort?

NRS

I responded by saying that I hadn’t scragged a mainspring in 10 years and I wasn’t about to, just to answer the question. Well, I’m not doing that, exactly, in this report, but what I am doing is closely associated. Today I start to answer your question, NRS. You are probably fighting battle bots by now, but for the record (not Rekord) BB does get around to it — sometimes.

And now for my pronouncement.

A coiled steel mainspring CANNOT be compressed farther than coil bound!

There, I have said it and now I will defend it. When a mainspring becomes coil bound, the steel coils are in contact with one another. For it to get any smaller, the steel in those coils would have to compress. Let’s look at some pictures.

scragging tool
This is as simple as it gets.  A scragging tool is a length of threaded rod, two large washers and two nuts.

When you tighten the nuts, you’ll notice that the spring really wants to twist. You have to hold both nuts with wrenches, and they will try to get away from you as you try to tighten them. This is spring torque, and sometimes it can be felt when certain spring-piston guns fire.

Where the mainspring lives

Now let’s look at where the mainspring lives. That plays a big part in this discussion, as well.

scragging powerplant cocked
This piston has been “caught” by the sear and is in the cocked position. The mainspring in this gun (there is no spring in there now) has this much space to occupy. Please notice that the outside of the spring is contained inside the piston and the inside of the spring is contained by the spring guide (removed here for a better view) and the piston rod. This is from an older Diana — a 34, as I recall.

scragging spring and tool
A mainspring next to the scragging tool.

What you cannot appreciate from the pictures above is what the mainspring looks like when it’s compressed. But when you scrag the spring, the shape jumps out at you. The spring tries to squirm away from the force that compresses it. Let’s see.

scragging spring in tool
And here is the spring in the tool.

This next picture is very important. Look at it and then look back at the picture of the cocked powerplant above.

scragging mainspring nearly compressed
See how squiggly the mainspring gets when compressed? But when it’s inside the piston, as shown above,  it can’t do this. There is nowhere for it to go! This spring is nearly compressed, but not quite.

scragging mainspring compressed
And here is the mainspring completely compressed. If you want it to get any shorter it will take many tons of pressure to deform the steel spring coils. This mainspring is completely compressed. There’s still a slight curve to the spring, which the inside of the piston and the outside of the spring guide will remove. Leave the spring in this tool fully compressed for four hours and it will be scragged.

What you have just seen is proof of why it is impossible to over-compress a coiled steel mainspring — just as a spring-driven clock can’t be overwound. Check it out online if you don’t believe me.

Removing vibration from a spring-piston airgun

What’s happening inside your spring-piston gun is that the mainspring is being held compressed between the piston and the spring guide. The more room there is, the kinkier the spring will be when compressed, and the more room it will have to shudder and shake when it expands. You will feel that as vibration. Remove the extra room, and you remove the vibration. That, my friends, is a big “secret” to tuning a spring-piston powerplant.

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But wait…

Here is where BB turns the tables and GunFun1 comes out on top! We have all read about GunFun1’s experiments with spring guns. Some time ago ( a few years?) he experimented with removing the mainspring preload from a springer and testing its velocity. And he took out a significant amount of spring without loosing anything. See, GF1? Old BB does pay attention!

Well, here is my idea. I have this mainspring that just came out of my Marksman model 70 breakbarrel. You will remember that it looked straight until I removed the spring guide and then the back of the spring got all hinky. Let’s look.

scragging hinky spring
Well, looky, looky, who’s got the cookie?

What we have here, dear friends, is an opportunity. BB told you that the end cap unit came out of the rifle about two inches when all tension was off the spring. And here we see that the bent end of the mainspring is also about two inches long. It’s not exact, to be sure, but it’s close enough for BB’s ‘speriment. Can you guess what B.B. Pelletier is proposing to do?

That’s right! He wants to whack off the last two inches of this mainspring, then dress the end and stick it back into this rifle. Then he plans to test the velocity again.

Is the old mainspring good enough for another 20 years? Probably not. It is straight — er, but it’s not perfectly straight. So old BB will put her back in the rifle but then take her out after 10,000 shots, or so. Yeah — like that is ever going to happen! When this air rifle has 10,000 shots on it old BB Pelletier will be a footnote in the history of airguns. And FWB 124s will sell for more than a thousand dollars! But perhaps we will get to see a little of what GunFun1 was telling us about mainspring preload.

Some more on mainsprings

There have been comments on this blog in the past about stretching springs to increase their power, and I want to address that. You can’t stretch a spring and increase its power for more than a few uses. What will happen if you try is that you’ll cause the premature failure of the spring. One or more of the coils will collapse, resulting in a canted spring. The results will be greater vibration and less power.

The metallurgy of a coiled spring is very precise and has not been covered in this report. There are things like forming techniques, heat-treatments and stress relief that are part of what make a spring capable of doing what it does; and while it’s possible to change the characteristics of hot-formed springs, we use springs that are wound cold and cannot be changed. When they reach the end of their life, they’re done and are not suited for reclamation except through scrapping. Maybe! But if BB’s ‘speriment does work we may all learn something more about coiled steel mainsprings.

One final thought

Manufacturing being the imprecise process that it is, every airgun powerplant will have slightly different dimensions — even within identical models. So, the length of the spring that fits inside the powerplant will change from one gun to the next. That’s why manufactured airguns cannot be held to tolerances as close as those that are tuned by hand. Some of the “slop” we see in off-the-shelf spring-piston guns is there to account for these small differences. That’s why an individually tuned gun can usually be made smoother and more powerful than one made by a factory process.

Summary

It’s important to get all the performance a spring has to offer since there’s no way of adding life when it reaches the end of its life — maybe. In the case of the spring inside a spring-piston air rifle, the scragging process can occur naturally during operation since the spring is nearly coil-bound every time it’s cocked. So, scragging doesn’t really add life to an airgun spring. However, since the spring we are talking about today has failed at just one place, I hope to determine whether there is some merit to what GunFun1 has told us.

102 thoughts on “BB’s ‘speriment: Part 1”

  1. BB
    If you cut those 2 inches off you could loose velocity.

    What happens when a gun has that extra preload it can be pushing the piston harder or I should say faster than what the piston seal can handle. So that means no extra power with that extra preload.

    But back to taking the 2 inch of preload off your gun. It could slow up because your piston seal on that gun could keep up with the extra spring pressure.

    So that is (not) a rule of thumb that taking preload out of a spring gun and having the same velocity as with the preload. The piston seal to cylinder wall fit plays a big part in velocity when your messing with spring pressure. It’s a balance that you have to find. And is another big part of tuning a spring gun. If that all made any sense.

    • GF1,

      I know that cutting off the whole two inches isn’t the right approach. It’s an “all or nothing” approach. But I can stack washers to get back some of the preload if I want.

      As for the piston seal, I still haven’t decided what to do. This one is in good condition, but a little hard. ATF sealant?

      BB

      • BB
        100% with you about going a little more than needed when cutting the coils.

        That way you tune the preload back in to the gun.

        I’m not going to tell you how many times I took a paticular spiring gun apart and put back together with different washers for preload to get the velocity and shot cycle how I wanted.

        If somebody gets a spring gun tune good on the first try with cutting a spring to reduce pre load I say bull. That gun is still no way as good as it could be. You got to chrono as well as shoot grooups to see what is happening with accuracy also.

        But as far as that leather seal goes to try to help get the best seal possible I don’t know. I have never did “speriments” with leather seals. But I have with using o-rings for seals in my FWB 300 instead of the cast iron ring they use to seal the piston. All I know is I have a very accurate higher velocity 300 that shoots very accurate beyond 50 yards.

        BB I know you know. There is some do’n go’n on when you take a 300 apart to change a spring or piston seal ring. You don’t even want to know how many times i had my 300 apart when i was trying different o-ring fit for sealing and drag and velocity when I was searching for the right o-ring. And one thing I guess I’m kind of proud with is that o-ring is still in my 300 for at least 5 years now. I myself wasn’t sure how long that o-ring was going to last.

        Oh and I’m going to say it’s been at least 5 or more years when I was cutting preload off of springs. That happened back on my first TX200 I had. And i know BB your biting your tongue right now. Who would ever mess with a perfect out of the box shooting TX anyway.

        Answer. Gunfun1. 🙂

        • GF1,
          I am curious as to the material of the o-rings you put into your “300”. I have a personal preference to Viton. The have a much lower tendency to take a set than Buna-N. Viton is relatively impervious to most fluids / lubricants and very good in a high velocity sliding seal if the surface finish is 63 rhr or better (almost mirror like) . I also like to use it in water systems though the cheaper material is EPDM. But EPDM takes a set much like Buna-N. FYI EPDM will degrade rapidly if subjected to any petroleum lubricant.

          BMW 🙂

          • BMW
            Not sure what type they were. They are the black ones. They are the same as what we use in our machine shop machines that run on hydraulics at work.

            And I have wondered about lubbing the 300 with the o-ring in it now. But I oil it about like all my other spring guns and with silicone oil. So far so good.

        • GF1,
          Since the o-rings are used in a hydraulic system, the typical commercial o-rings are Buna-N. The typical time to failure of a Buna-N o-ring is 8 to 10 years of under continuous pressure, due to set ( o-ring takes a permanent change in cross-section shape ). But under cyclic pressure 2 to 3 years less, friction wear on the o-ring surface. The primary failure mode is a slow leak that quickly becomes a problem particularly with hydraulics ( flammable ). The Viton o-rings would typically last over 15 years and even longer. This is the time to failure under nearly continuous use. Though the time for a o-ring to fail in set is a function of compression of the o-ring and time only.
          The use of Buna-N is not detrimental to the piston and cylinder. The use of silicone is actually better than hydraulic oil for the longevity of the o-ring in a sliding application.

          BMW 🙂

          • BMW
            We use Viton seals at work also.

            And somebody needs to tell our machines at work they are suppose to last 8 years. Haven’t seen that in the 37 years I been working with them.

            So far my 300 is on a roll though. Happy about that. 🙂

        • GF1,
          8 to 10 years is the expected life of a Buna-N under continuous use (24 hrs a day 365 days a year) and at an oil temperature between 130 F and 180 F. This pushes Buna-N hard in a sliding application the surface of the o-ring will approach its upper temperature limit of 250 F. The closer you operate to the rubber’s maximum temperature limit the faster the material degrades. Viton on the other hand has an upper temperature limit of 437 F well above the typical hydraulic fluid temperature. So the Viton o-rings in your “300” should last a very long time.

          BMW 🙂

    • GF1,

      You lost me. That’s OK. I myself do not grasp what you are saying in “But back…”

      Now, as for the fit of the piston seal to the cylinder, this has a leather seal. It will conform to the cylinder. It would be an interesting experiment to see which works better. I can think of at least one of the old gals around here that would be perfect for that ‘speriment.

      Some airguns have been given more spring load to increase their velocity. This is a quick, dirty and cheap way to do such. Much, much cheaper than doing it the right way. Of course they can only take it so far and they become coil bound. Then you MIGHT be able to switch to a different spring that has the same size wire, but fewer coils per inch and a higher tension. I am not sure that is the correct way to say that. What I do know is the science of springs is a very deep subject.

      • RR
        What I mean is the spring can over power the piston seal at some point.

        What happens is the piston moves forward real fast with all that extra spring preload. The piston seal builds the compression in the cylinder before the pellet moves but there is also resistance before the pellet moves. So now all of a sudden air is blowing back past the piston seal (blow by).

        That is wasted energy. So now if we take preload out a little at a time it will slow the piston down. Now that gives the piston seal a chance to seal better and let all that excess pressure not bleed past the seal.

        The right preload is very important. Not only what we are talking about but also shot cycle which can affect accuracy. Again another reason to tune a spring gun by spring preload.

        Going a little deeper than I think BB was talking with this blog report but all related.

        But one thing I know for sure. And where BB was going. Coil bind is not good. 100% I know that. Imagine what is happening to the top hat and what the notch on the piston rod is doing that catches the sear. That notch and rod is getting stretched just like a valve stem on a car engine with coil bind. Eventually something will break. So no coil bind for ole Gunfun1 in airguns or engines if I have my say in what is getting tuned.

    • Massive amount of technical stuff in the comments this weekend. I’d like to humbly throw out another theory as to why cutting the spring shorter may not always result in lower velocity. I’m not sure that the piston seal is experiencing “blow by”. I think its more likely that the pressure being created is too much for the pellet to resist before its simply blown out of the barrel. Its like having 3000psi available, but the pellet only needs 1500psi before its already shot out of the barrel. I think you’re just trimming away this extra, unusable power from the spring. The gun was essentially “over sprung” for that given spring preload, piston weight / seal, transfer port restriction, flow dynamic, pellet weight /bore fit, barrel length… I don’t know. I’m probably getting out in the weeds here. I guess I’m saying when you cut the spring shorter and shim as necessary, you’re optimizing that particular spring rate to the rest of the system.

      • Derrick
        At some point in time the seal is not going to keep up with the piston movement by the spring.

        No matter what pellets you been shooting. The blow by will happen to some degree as time goes on. The seal will wear.

        Remember BB asking me at the top of the comments what should be used to restore the seal to help it seal better.

        Blow by will happen.guess what even with a new piston seal.

  2. B.B.,

    My instincts tell me after whacking off 2 inches from the spring you are going to need a half inch of preload to get to where you want to be.

    Siraniko

  3. BB
    I don’t wish to offend someone but the terms are “Rocket Science” and “Brain Surgery”. Been that way for as long as I can remember.
    Both very challenging subjects. One is hard to figure out the other is hard to accomplish. Someone on TV just mixed them up also.

    I agree with RR above. Springs would fall under “Rocket Science” 🙂

    Tom, getting old has a new clarity for me. It’s feeling the same as you did before you had your 8 hrs. of sleep.
    Bob M

    • Bob M,

      “Rocket Surgery” is intentional, a clever play on the cliched “It’s not rocket science” and “It’s not brain surgery.” Other examples of the technique could be “change gamer” and “chew and walk gum at the same time.” Another is the moving of one letter, the phrase “bass ackwards.”

      Michael

  4. Mr. B.B., if someone wants to supply the ammo (hint, hint, P.A.), I would be happy to try to put 10,000 shots through that rifle for you. For the sake of science, of course. :o)

  5. BB

    I love ‘speriments!

    Thanks for sharing this one! This pictures and explanation really clarify what is going on inside our beloved springers!

    As kids our springers saw a lot of use (500 pellet days were typical) and were often in a cocked state for hours. Not surprisingly, scraged springs were common.

    I tried a few things to revaitalize the springs and boost power. As you pointed out, stretching the spring was a short lived fix, adding washers to increase preload worked pretty well but the best thing was to install a new spring.

    Back then, a lot of my “gunsmithing” was installing replacement (and upgraded) springs. I used to charge 5 boxes of pellets plus the cost of the spring to do the job. A “Van-Tune” (clean, deburr, polish and moly) was 3 boxes – which, at that time, was worth about $1.50 🙂

    Hank

      • LOL! Good one Roamin!

        “Van” was my nickname when I was a kid.

        My friends started the “Van-Tune” thing because the airguns I tuned were smoother and faster shooting – guess they thought it was worth identifying.

        Vana2 is the call sign I use when flying WW2 fighters on-line.

        Hank

        • Hank,
          Where did “Van” come from? All the people I know with that nickname are Greek-Americans named Vangelis. But that doesn’t relate well to Hank, which is itself a common nickname for Henry.

          • Roamin,

            The “Van” comes from my surname, I’m Dutch and many of the names are prefixed with “van” or “van der” which means “from” or “from the” (family of). Similarly, German names often start with “von”

            The van and the der are (properly) lower case and spaced from the actual surname.

            I’ve long since given up on the “proper” form on my name and just spell it as one word with the “V” capitalized – saves a lot of confusion 🙂

            Not surprisingly, my friends shortened my name to “Van”

            Sorry you asked? LOL!

            Hank

          • Hank, the blog won’t let me reply to your comment of 7/11 at 9:51 am, so I am replying here. Not sorry at all. I find this stuff interesting, too. I should have considered a nickname based on a last name. Anyway, enjoy the rest of the weekend!

  6. BB

    Guess I missed your point about overwound clock springs. Us old folks had watches that were spring powered. We all dreaded binding the works believed to be the result of applying too much force to the winding knob.

    Deck

  7. BB,
    The engineer in me coming out again.
    Things to remember about springs.
    1. The spring constant is not truly constant even for a linearly wound spring. The slope (spring constant) of the force (y) versus distance (x) is approximately linear away from the extremes of travel. The initial travel ( a relatively short distance ) the spring constant is increasing to its linear value and near the end of travel before the bound coil point it is increasing again. The potential energy available is the area under this curve for the specific values of initial x (preload) and final x ( airgun cocked ). If you remove coils you are removing the maximum potential energy available to airgun system.
    2. The spring constant (Hooke’s Law) also assumes zero mass and zero friction. The reality is that the spring has mass and friction even by itself and operating in the nearly linear region of its spring constant.
    3. Springs age, the spring constant slowly degrades. The only way to restore a spring is to return the metal to its original state. This is a very difficult thing to do, controlled temperatures, and controlled cooling rates, and money. The easy and invariably cheaper / less expensive way is a new spring.
    4. To have more potential energy available hence more velocity a higher spring constant is required. But this has limits, space available ( inner diameter of the spring tube and outer diameter of the spring guide ), maximum wire diameter ( that can be effectively wound to the required dimensions with sufficient clearance to allow compression of the spring ), and finally the amount of cocking effort the cocking mechanism can safely withstand.
    5. Any spring mass system can be improved by reducing friction, this in a airgun helps in ways you have explained far better than I ever could.

    What Vana2 stated adding washers to increase preload is not exactly what is happening. The spring constant has decreased and adding washers moves the fully compressed stated closer the being coil bound. This has the short term effect of restoring the available energy.

    BMW 🙂
    Finally done editing. LOL

    • Bmwsmiley, I’m not an engineer, but I can appreciate your thinking. I think showing a couple of graphs and the area under the curve you mention would help show the difference in potential energy of a whole spring vs. a cut spring.
      Re #1: Could it be that the original spring has more potential energy than needed to push the pellet out of the barrel at a desired velocity, which may explain why GunFun was able to cut back his springs a bit with no loss of velocity? I’m thinking that perhaps even though you might lose some potential energy, perhaps you don’t need it all to make things work in the first place.
      Re #2 and 5: It seems to me, that the pellet has mass and friction too as well as the piston and seal, so would that affect the spring? Certainly we can understand from your comment how Tune in a Tube would increase the mass (and maybe the friction) of the spring, which gives a gun less velocity.
      Re washers: why would the improvement be temporary? Would adding washers decrease the life of a spring compared to not adding washers?
      Finally, if I remember the earlier parts correctly, B.B. was not getting the expected velocity from this gun, so perhaps nothing will realistically restore the gun except a new spring. Would you agree?

      • Re # 1 you are referring to the other part of the system, which has air flow thru a port limiting the maximum mass flow rate and hence the velocity of the airgun pellet. This assumes that the air flow is choked, velocity at the narrowest point is at sonic velocity for the given pressure and temperature. In a choked conditions, an increase in inlet pressure (piston velocity) does not alter the mass flow rate and therefore pellet velocity. If the flow is not choked, an increase in inlet pressure (piston velocity) will increase the mass flow rate and therefore the pellet velocity.
        Re #2 and 5 The pellet is on the air side of the system and will not directly alter the main spring mass assembly but you are correct that the piston and seal are part of that system. Though a small amount of Tune in a Tube (grease) will reduce friction an excessive amount will as you suggest will increase friction and mass and therefore reduce the energy available to the air side and hence less pellet velocity. The whole system; main spring, piston, seals, air flow passage to the barrel, barrel and finally the pellet are all one system and small changes will alter the performance of the pellet. Assuming a fixed mass for the pellet, a pellet that seals poorly will a lower velocity compared to the pellet that seals properly. Though friction is higher, the velocity is also higher. A poorly designed or manufactured air passage will also reduce the velocity of the pellet. That is why if you round the edges and smooth the air passage to the barrel you will improve the velocity of the pellet.
        I tried to get the plots but I failed see next comment / reply about the washers.

      • Roamin Greco,
        Sorry I forgot to add your name to the 1st one.
        Re washers; the amount of energy being stored by the spring is a function of the initial preload plus the compression when cocking. The energy of the preload cannot be used in propelling the pellet, only the compression when cocking. The washers increase the preload but it also pushes the total spring compression closer to coil binding. The picture shows the initial non-linear portion which is part of the preload. The other shows the entire compression including coil binding. When a spring is scragged it is plastically deformed, normal use the spring is designed to stay in the elastic and relatively linear portion of the curve. Note these curves are not generated by actual data but an exaggeration to explain what is happening. The closer the spring is to “coil binding” the faster the spring will age. Every spring under compression/extension will slowly reduce the spring constant. This will eventually cause a reduction in performance.
        Spring replacement, is required based on the photo, it is bent. This cannot be easily corrected. The removal of the bent section and adding spacers to add preload without coil binding will allow the airgun to be used but in the near future performance will again drop. How long? Too many variable to predict. It would be useful to know the as designed unloaded spring length to compare to the current state of the main spring. But I suspect that is not readily available.

        Since the airgun is apart, I would (car term) port and polish the flow passages to improve performance.

        BMW 🙂

        • bmwsmiley, I appreciate the time it took you to tap all that out, plus the graphs. You really have me thinking. So if I look at your graphs, even if you cut a spring, there will still be a pre-load portion of the curve and a linear portion, and a coil bound portion, but the entire distance will be shorter. In the case of the Marksman 70, B.B. discovered, “that the end cap unit came out of the rifle about two inches when all tension was off the spring. And here we see that the bent end of the mainspring is also about two inches long.” If I understand the graph, the first two inches of the spring’s travel is taken up by this preload. But cutting the spring shortens the entire curve so you will be starting at the preload section, which gives you very little in return for compression distance. Adding washers takes up the preload, but since the overall spring is shorter, it will never achieve the same potential energy as the original spring because the curve is shorter and does not rise to the same heights.
          I’m trying to understand how GunFun1 was able to cut a spring, add washers and get the same velocity. perhaps the longer spring was never compressed to near its coil bound state, so its maximum potential energy was never realized. More later.

          • All of the prior comment is basically me thinking “out loud.” Applying it to the Marksman 70, it seems to me that to maximize the potential energy (if that’s the goal, but not necessary B.B.’s goal) you could put the cut spring in B.B.’s threaded rod contraption to see how short the spring gets before it is as close to coil bound as you care to go, and then add the distance that the cocking mechanism imparts upon the spring, and the rest is room for washers? I guess what I’m getting to is to arrive at an effective max and min thickness of washers needed to get the Marksman going again without losing too much velocity, or perhaps gaining a bit?

          • Roamin Greco,

            Imagine pushing syringe. The volume contained within the syringe is fixed. The force applied as you push the plunger is variable. That is the spring. So a stronger spring will push the plunger (piston) faster but there is a point of diminishing returns where too much spring ends up coil binding with increased friction resulting in less force applied to the piston. Gunfun1’s modification most likely accomplished the reduction in friction from the expanding spring as it was compressed resulting in a faster travel of the spring resulting in less twang and excess force slamming on the piston when it ends it’s travel.

            Siraniko

    • bmwsmiley,
      As a retired engineer (electrical, not mechanical), this detailed explanation made me feel like I was back in engineering again…thank you for that.
      Take care,
      dave

      • Dave,
        You correct, I am a retired mechanical engineer of sorts, actually a Nuclear Engineer via education at Purdue, an electronics technician via Navy training, and a carpenter/plumber/electrician/mason via training from my Dad.
        Just a poor farm boy from the sticks of Southern Illinois

        BMW 🙂

        • bmwsmiley,

          LOL! I’m just a dumb ol’ country boy. Actually, in today’s terms I am an Appalachian-American.

          Except for the Purdue thing, I have the same credentials. I went to “Dabney Tech” for a little more in electronics and a whole bunch of OJT. My wife says I am semi-retired. With this Chinese bioweapon running amok, I am working from home. I ain’t going back in the box.

  8. B.B.,

    I might have an additional, unrelated experiment for you to perform and write about after you complete this one. I recall your observation a few years back that springs with a kink at the end eventually break in the air gun. A sign this has happened is the rifle becomes easier to cock and smoother to shoot.

    I remember something about the broken end threading itself into/onto the remaing spring, essentially becoming a top hat. That and the reduced preload make it, for the time before it malfuntions completely, a better shooter. Of course before the break, the kinked spring no doubt made it vibrate, too. Therefore, the smoothness might feel even more smooth because of the contrast.

    Anything to mess with there? :^)

    Michael

    • Michael,

      The springs I was talking about were in Dianas and they didn’t kink. They were so hard they fractured at both ends and did become easier to cock and also smoother to shoot.

      This one probably won’t break and I want to get the bent end out so the spring is reasonably straight again. So probably nothing to mess with. But thanks for thinking.

      BB

      • BB,

        Per Michael’s comment of a broken spring (mid break) winding itself into the other half,…… why not do that to maintain the factory flat end?

        I was never comfortable going to a stepped end (even if flattened as best possible) unless a new spring kit had the newer style stepped seat.

        Just a thought,…….. Chris

        • Chris,

          You can insert thin washers under the “cut” end, most especially if it is flat. A little moly between may even make them slip on each other.

          There are two other solutions available. Once you know your desired length, there are a few folks who can properly cut, bend and forge the end of your sproing.

          There are also companies that can sell you a custom sproing. Give them the wire size ID, OD and length you desire and very soon you have exactly what you desire at a very reasonable price.

          A flattened coil is a better end, but a properly cut sproing can be used if done right.

          • RR,

            Yea, the washers are the easy way to go. Precision ground being best. If done, I lubed the center (of the 2) and left the outsides dry. The idea being is that it would force the rotation to the center. A set up at each end, if possible, is ideal.

            Chris

        • Chris,

          It is really interesting the various ways manufacturers and us shooters have come up with to eliminate the rotational torque.

          Some manufacturers have used freely rotating pistons. If you were to insert one of those bearings we have talked of around here under the other end of the sproing, you would have a “free floating” arrangement that would solve the issue.

          Another “simpler” way is what was done with the FWB300 series. They used two short counter wound sproings with a connecting bushing in the middle. The two sproings twisted opposite of each other with the result being the piston and the air rifle received no rotational torque when the sproings were released. Quite ingenious really.

  9. B.B.,
    I love science. In a nutshell, the scientific method consists of having an idea, and running a controlled experiment that either confirms it or indicates the need of a new one. My gut feeling – not exactly scientific – is that leaving a 1/2″ or so of preload will be the goldilocks point for this particular tired spring. So, my suggestion is to cut the spring in two steps, testing in between. Besides, using a hacksaw is good for . . . nah, ignore me. 🙂
    Henry

  10. I think it’s great to turn prior comments into this “speriment.” Can’t wait to see the outcome. I would love for this to end with a cloverleaf group to match the one that came with the new rifle in the box. That would be satisfying!

    Are replacement springs or Vortek kits readily available for this model? Y’know, just in case the ‘speriment’ goes awry, you will have a Plan ‘C’ (because you skipped Plan ‘A’ and went straight to Plan “B.B.”). Ha-ha.

    • Roamin,

      Define “readily available.” Does it include people on the planet who have actually seen one of these rifles before? 😉

      Fortunately, mainsprings are fairly common items and can be made to work in platforms they were never designed for. Which is good because I suspect that is exactly what the folks at Weihrauch were doing when they made these up!

      BB

      • RR
        No place to reply below about the spring gun rotating.

        I believe that is why FWB put 2 counter wound springs with a spacer in the middle on the 300. To help tame rotation of the spring and gun.

        • GF1,

          Persactly. That is what I just commented to Chris.

          Another way is to have a freely rotating piston. Combine that with that flat bearing we have discussed here and you have a “free floating” system that theoretically should transfer zero torque.

          The FWB method to me seems to be the most cost effective way to solve this issue with the exception of the piston rod used in many to engage the trigger assembly/sear.

          This brings us back to the free to rotate piston and the bearing under the sproing end. I can understand why the manufacturers do not use the bearing as this would add considerable cost, but the only reason I can come up with for not using a free rotating piston could be additional machining cost.

          • RR
            Chris sent me a couple of the flat washer style needle bearings.

            I put them in my TX200 and it did seem to calm the gun some and seemed like a more quiet shot cycle.

  11. B.B,
    I was wondering if the spring twisted when compressed, resulting in more coils , so I counted the coils in your photos. I found that the number of visible coils did not change. So no twisting occurred. Instead it appears that the diameter of the coils increased.
    Please measure the outer diameter of the spring when compressed and uncompressed.
    Thanks. – Don

      • Chris,
        Thanks for your comment. So there is some rotation when the spring is compressed. If the tube limits the diameter increase, then I suppose that there will be more twist. – Don

        • Don,

          As best I get,…. it will twist,… if it can. If restricted,… then we are talking stored twist/energy. To what effect?

          The reason I did it was to see for myself. Nobody seemed sure. 1 twist? 2 twist? 3 twist?

          To me,.. at least one end better be able to rotate freely. If not,… I guess it could be imparted into the body of the rifle,… as many speculate.

          That is as much as I got on the matter.

          Chris

          • Chris,

            I do believe you are correct in this matter. I have had a few sproingers with a strong desire to rotate when fired. If not mistaken, the piston in all of these was prevented from rotating and I would bet real big money that no bearing was installed on the other end.

  12. Today I put the .25 caliber Lothar Walther barrel on my low pressure pellet gun to see what kind of accuracy I could get. Well it took a few days to get the barrel fitted to new bushings. I also had to build a new valve I split the threads in the old one where the quick disconnect air fitting screwed into the tee. I did not use any pipe dope or Teflon tape to seal the threads so eventually I over tightened the brass bushing to stop it from leaking. The new valve uses a full 1 1/4 inch tee with PVC bushings from 1 1/4 PVC slip/socket to 1/2 inch treads for all three fittings. That should give a stronger threaded fitting all around. One thing I did not consider was the 1 1/4 PVC tee is longer than the 1 1/4 tee with a 1/2 inch threaded side fitting. The new valve has a little more volume than my original valve.

    My plan was to build a set of bushings that both the .22 and .25 caliber barrels will work in. I fit the bushings to the .25 caliber barrel and then found out that the .22 caliber barrel has a slightly larger outside diameter. Both barrels are supposed to be 0.63 inches or 16 mm outside diameter the one barrel is too big to fit in my bushings. The difference is probably extremely small. I reamed the bushings until they almost fit the barrel and then honed the bushing to the final fit. I can not feel any slop in the barrel to bushing fit. With a good dollop of grease on the barrel at each bushing it slides forward and back against the seal like butter.

    One note the Lothar Walther barrel blanks do not come with a leade. the barrel is cut off flat against the rifling. They do come with a good crown though. I had to make a leade for the .25 caliber barrel before I could get a pellet started in the barrel. I drilled out about 1/2 a pellet length of the leade with a .25 inch drill bit and then made a small chamfer with a large drill bit followed by some polishing with a felt tip and some polishing compound. It is still a tight fit with the pellets I have.

    The only .25 caliber pellets I have are Beeman Kodiak 31.02 gr domed. I will need to order a supply of .25 caliber pellets to do more testing of the .25 caliber barrel.

    When I make the bushings for the .22 caliber barrel I will weld them on a bracket that I can adjust in all three dimensions. That should end up as good as I can get with my 2×4 wood frame. I used to have a stack of aluminum I beams that would have been perfect for a frame but I scraped them a few years ago and I never throw anything away.

    Ok Gunfun1 here is the .25 caliber Lothar Walther barrel test. At 100 psi I was barely getting over 300 feet per second so I cranked the pressure up to the 147 psi max for the rest of the tests. At 147 psi the average velocity was 406 fps the spread was 7 fps and the SD was 2.39. The energy was 11.4 ft-lbs.

    The targets are shown below. Each target has five shots. The 10 yard target was difficult to measure. With the 25 yard target I was able to see the oil marks on the paper so that was easier to measure. I probably won’t be doing much more with the .25 barrel until I get some more pellets. I am about out.

    Don

    • Benji, nice results I think. Clearly a stabilised flight. The extra 47psi makes it right at the legal limit too, 12 ft/lbs. I am curious if using 3 cut and finished springs would perform with better dura bility over the traditional one spring. The place where the coils kink is around 2 inches, so I would try 2@that length, the third one is a bigger spring.
      I am making a portable shooting cart out of a folding harbor freight hand truck.
      I mount the carbon bottle horizontally with webbing and carabiners, at a convienient height, and I am mounting a removable base to hold the monopod. It made from an old floor pump with just the base and the top of the compression tube cut off, the mono pod fits inside the tube perfectly, and stands up on it own when it is removed fromt the cart. It can be used separated or attached. The shooting stick can be adjusted high enough for standing prone. I still need to add a gun rest for refilling, gun rack style . I am glad you are also keeping busy!
      Rob

        • So, my android will not let me reduce file sizes, from 4 to less than two . Let me upload them to the pc. It has no image management software on board. Brand new samsung s71
          That’s why you get an apple. Doh!
          Rob

          • I myself prefer to use my Canon and then upload to a PC. I do not own a “smart” phone. I still use a “Star Trek Communicator”. It works great as a phone and is quite compact.

    • Don,
      I have been following your experiments and I continue to be amazed at the results. I would never have imagined 12 ft-lbs plus from only 147 psi. The spread is also an indication of a very consistent valve, and that shows in the accuracy.
      Thanks for letting us be observers of your work!
      Henry

    • Don
      Dog gone it anyway you got me. I can’t stop thinking about the results.

      First I’ll have to say you did a good job on doing the lead in on the barrel. And that 11 fpe is great. I did a .22 caliber discovery barrel and steel breech on a 1322 one time with a 1399 stock. I would do like 4 pumps and the 16 grain pellet would just lob out to the target. You could see the pellet in flight through the scope no problem. It was dead accurate at 25 yards like your results. The starlings didn’t stand a chance at 25 yards. It would hit and they would fall right over and the other starlings wouldn’t even move and they are skitish birds. Quiet was part of that to so the other birds didn’t get spooked.

      So that was something I would like to know about this .25 caliber setup tou have now. How loud is it?

      And Don if you don’t take this low pressure air gun somewhere somebody else will. You need to make it happen some way to make it a production gun.

      I’ll say it again. Definitely like what I’m seeing. I always had a feeling deep down inside after shooting bb’s and such out of our air nozzles at work with a tube attached. Pretty accurate and for sure hard hitting. Don I believe you done it. Now get it happening so anybody who wants one can get one.

      • GF1,

        My valve is designed to maximize velocity. The valve is still open when the pellet leaves the barrel. Even so it is fairly quiet. With the .22 barrel and lower psi the gun was quiet. I don’t see this gun working without being tethered to a compressor though.

        With your skill set you should build your own. Maybe when you retire. I am very impressed with the Lothar Walther barrel blanks in 16 mm O.D. I will order a .177 barrel when they are in stock.

        • Don,

          Now you need to work on your valve closing by time the pellet exits the barrel. You are on the right trail to how the original PCPs operated. There secret was a timed valve that opened for a set amount of time. This way they were able to have a reservoir containing only 600-800 PSI and still hurl large projectiles (.45+) at velocities that often exceeded 600 FPS with enough accuracy to bring down large game at considerable distances.

          I often dream of owning a .45 or larger PCP air rifle that I could fill to around 1000 PSI and have two or three good shots out to 50-100 yards.

          A couple of the “boutique” manufacturers explored this, but the major manufacturers have not as it requires more engineering to accomplish this. It is much easier to up the pressure to achieve such.

    • Don,
      Very cool! That’s another thing I love about this blog: seeing what some of you crafty and skillful readers-of-B.B.’s-blog come up with on your own. Very impressive. =>
      Take care,
      dave

    • Benji-Don, nice work! I sent you a message on today’s blog, but it looks like you have this thing working pretty well. Good for you. And fun for us to watch your progress. Now stick a cordless compressor in a backpack and make a low pressure air mini gun! You will have to change your handle to Benji-Aaaarnold-Schwarzenegger!

  13. Benji-Don,

    What an Odyssey into the Land of lpa you are on Don.
    That is some stellar performance out of your testbed.
    What fun to be allowed to watch over your shoulder as you travel this path.
    Looking forward to lots more glimpses over your shoulder!

    Thank you!
    shootski

  14. Hey B.B.,
    I didn’t see a new blog for today (the 10th), so I started praying for you, that you are OK and all…
    …and then I realized that today is Saturday, LOL! Well, that’s what happens when you retire, you lose all track of days, like which are the weekdays, and which are the weekends, because they’re all just another day off. =>
    However, it’s all good; I figure a few extra prayers for your health and well-being are always a good thing. After all, you are providing a much-needed and well-appreciated service to the airgun community, and we’d all like to see you keep on doing so for a good long time to come. =>
    Take care & God Bless,
    dave

  15. Well from reading comments people have alot of faith in piston seals.

    It seems that the pellet has the least resistance than the seal by the comments.

    From what I gather the pellet is more inconsistent when moving or sealing than the piston seal.

    To me the piston sealing is way more consistent compared to pellet seal and movement.

    So what one is making more blow by than the other?

    • Yeah, I think you’re right about that. So, one accuracy component that we’re looking for is a pellet that gives a very consistent resistance at the breech?

    • Gunfun1,

      I have been thinking about this comment of yours: “From what I gather the pellet is more inconsistent when moving or sealing than the piston seal.” for at least a few tens of minutes!

      So take the piston seal out of your statement and for this discussion replace it with a precision metered volume and pressure charge of air. Then the only thing left is how consistent the projectile seals to the bore. With pellets the skirt may blow out to the bore diameter (grooves) not at all, partially, or completely depending on skirt uniformity in thickness and the metal’s degree of malleability. So not only blow-by but also variations in bore drag can occur.

      Just for comparison shooting bullets from airguns requires very careful projectile diameter matching (fit) to bore size just to overcome the probable lack of obturation at currently achievable initial bore pressures. But if too large (or long a contact area) the bore drag kills performance.

      If the pellet skirt blows out you have a hollow based bullet traveling down the bore.

      I hope your happy now! All that visualization gave me a headache. I will go and fix that with a nice two fingers of Woodford Reserve (neat) with a glass of water (no ice) on the side ;^)

      shootski

  16. The relative power generated in a spring piston is from the volume of air being pushed by said piston. How fast that piston moves that volume of air is predicated by the weight of the piston and the power of the spring. The power of the spring has a narrow band to work in. Too much spring will cause coil binding. Too little spring will not use the volume properly. Some springs are prone to break with no preload due to excessive pogoing within after firing. Finding the Goldilocks zone that will produce the desired power without excessive vibration is the aim of all tunes. Some have gone to lightening the piston along with lessening the preload of the spring. The next part to deal with is the relative friction of the pellet to the bore of the barrel. Soft lead pellet is best in a proper sized bore. Hardened or oversize pellets might require more convincing before moving. Are my thoughts and understanding correct?

    Siraniko

  17. “Are there airgunners who are equivalent to weekend bikers? That is a legitimate question, if there are casual air gun hobbyists who do not hunt or compete but desire a fine sporting airgun, suitable for field target, or a 10-meter target air pistol, simply for backyard plinking. That certainly describes me, although I suspect there aren’t many like that. (If any readers fit that description, please comment below.)” — Michael (in “The High-End: As Good as They Can Be: Part 2”)

    Hey Michael,
    I meant to comment on that, but looking back, I never did. Actually, I am one of those weekend bikers; one of my Harley buds, Rick, let me borrow his Harley, and I got a hankering to have one of my own (which my wife got me a few years later…my wife is awesome!). But the first time Rick got me to go to Bike Week in Daytona, it was not what I expected at all; I saw a sign, “Welcome Bikers!” as we pulled in to town, and I also saw two guys on Main Street with a cross that said, “Jesus loves you!” and as we pulled into a parking space, one lady hit me for a $10 to park there, and one on the other side hit me for another $10 for a t-shirt. My first thought was, “If a real one-percenter biker saw what I just saw, he’d run out of town screaming, LOL!” Don’t get me wrong; Daytona is a ton of fun, I’ve been there many times and I love it; but it’s more suited to weekend bikers like me, to “Wild Hogs” guys, than to “Hells Angels” types.
    In fact, now that I live in Georgia, when we leave Daytona, at the last stop sign, right before Rick goes south and I go north, we bump fists and yell out, “Wild Hogs!” Yes, cheesy, but fun. =>
    Anyway, getting back to airguns, I don’t own an Izzy, or a precision 10-meter air pistol, but I do have one fairly expensive air pistol: my PA-gifted-from-my-wife 1377 got sent to Mount Air Custom Airguns, and came back with a custom 12” barrel, custom internals, custom sights, custom 1-pound trigger, and custom rosewood stocks. I have a friend, whose wife I’ve known longer than he has; and if he brought this gun home, I know exactly what she’d say (after first giving him a Gibbs slap to the back of the head):
    “What’re you, crazy?!? You spent $500 for a bb gun to plink at stuff in the backyard! That money should have gone into our kids’ college fund!”
    I love her, but that would be her reaction. Conversely, my wife’s reaction was (as I was opening the box with the returned pistol), “What?!? That’s a lot of money…,” then, seeing the finished pistol, especially the Hank-type (Vana2) grips: “Oh wow! That’s gorgeous; what a work of art.”
    Me: “Yeah, the guy who owns Mountain Air was able to get me this set of grips, the last set made by his friend; he’s got lung issues due to wood dust, and won’t be making any more.”
    My wife: “Then you should treasure this.”
    And I do; I just wanted a nice pistol (that was more accurate than I was) with which I could enjoy a nice plinking session whenever the mood suited me; and when I shoot this gun, I lift up a prayer of thanks to the two craftsmen who made it possible.
    Thank you for the great guest blog!
    Happy shooting to you,
    dave
    P.S. My old arthritic fingers aren’t what they used to be; so today, I heisted the Crosman trigger shoe off of this 1322 (formerly 1377) and moved it to my Tempest to see if it would help out on that gun. Fantastic! While it doesn’t reduce the trigger pull, the ½” wide shoe on that 3/16” wide trigger spreads the force out so much that the trigger is much more predictable, easier on my finger, and makes it much easier to wring all the accuracy I can from that little gun; hence, it won’t be coming off. But thankfully, since, as B.B. has pointed out, “We are living in the Golden Age of Airguns,” I was able to hop online and find a replacement in a matter of minutes. I may be having trouble finding firearms ammo, however, thanks to airguns, I never go a day without shooting…yay for airguns! =>

      • Dave,

        I do have an Izzy. Over the years I have owned a few 10 meter air rifles. Why? For the same reason you stated. I want something that shoots better than I can. If I miss, it is me.

        Now, as for building up a relatively cheap airgun into an eye popping, very accurate shooter, I have a couple in progress right now. I do need to get me a couple of those trigger shoes though.

  18. ATTENTION! ATTENTION! WHOOP! WHOOP! WHOOP!

    BIG NEWS FLASH FOR ALL AIRGUNNERS!

    The 8th Annual North Carolina Airgun Show will be held October 15-16 2021 in Newton, NC!

    This is one of the biggest airgun shows I have ever been to. There will be four rows of tables stretching for almost 200 feet each. It will take you several hours to see all the airguns and paraphernalia there is. I have seen airguns from the 1700’s up to the latest and greatest.

    Be there or be square!

    Oh, I almost forgot. There is a shooting range out behind the building where you can bring your own or try out some of the airguns there for sale. We are talking over 100 yards of open ground to shoot.

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