Your input desired on design of barrel friction experiment with bullet coatings

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Michael Courtney, Nov 6, 2011.

  1. Michael Courtney

    Michael Courtney Silver Member

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    We've developed a method to accurately determine the average frictional force between the bullet and the rifle bore that is accurate within 1-2% and requires about 20 test shots to determine the friction of a particular bullet/coating/bore combination.

    Naturally, our next inclination is to quantify the barrel friction resulting from different bullet coatings: HBN, Moly, and WS2. We are leaning toward testing each coating in each of two bullet designs, a conventional jacketed lead bullet and a solid copper bullet in our .223 test rifle. Of course, the rifle barrel will need to be thoroughly cleaned when moving between coatings and before beginning.

    A few questions, if you are willing to lend your advice to our experimental design:

    1. Should we also test lubalox, the Combined Technology coating? This would constrain our design to one of the .224" bullets available from the factory with this coating. We would also obtain the equivalent uncoated Nosler ballistic tip and get them coated with the other three coatings. Frankly, we'd prefer not to test lubalox, because it locks us into the ballistic tip, and we'd rather test a match bullet from Sierra, Berger, or Hornady. On the other hand, we do think Nosler might be exaggerating the friction reducing claims of lubalox and it would be nice to debunk test the claim.

    2. In order to enhance uniformity (because we have so little bullet coating experience), we plan to send the bullets to NECO for moly coating and SSS for HBN. Is there a commercial service that offers WS2 coating, or do we need to roll our own here? Perhaps you can suggest someone with experience coating bullets with WS2 who might be willing to coat a couple of boxes for us. Is WS2 even still used as a common bullet coating? Is it a waste of time to test it, or is there interest?

    3. Our .223 Rem test barrel has a 1 in 12" twist which limits us to bullet weights up to 69 grains at our test facility. (We can shoot heavier bullets because of the thin air up here.) Is there a particular match bullet you'd recommend. A bullet with the most uniform bearing surface would be optimal, because preliminary testing (uncoated bullets) suggests that bearing surface has an impact on friction, and it would be optimal to minimize confounding factors so we can emphasize the effects of the coating.

    Of course, any other insight or advice you can offer would be greatly appreciated.
     
  2. royinidaho

    royinidaho Writers Guild

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    I don't have any experience whatsoever with handling, loading or shooting coated bullets.

    Having said that, I'm experienced in innovative activities such as your's.

    More power to ya!

    Much will be learned from your innovation. Who knows what will be revealed from your work.

    As one who exists where bore friction and jacket torture are an everyday major consideration I will be looking forward to what is learned from your work.

     

  3. Loner

    Loner Well-Known Member

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    I would easily forego the Noslers. Anything that really adds a noticeable improvement or change catches on. It only took a few years for moly's characteristics to get sorted out.
    Would be nice to see some real data. Have fun with it.
     
  4. Edd

    Edd Well-Known Member

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    I don't have any input regarding your testing but if barrel friction is an area of expertise for you, perhaps you could help me understand something I was told about friction in a barrel.

    I don't understand why the friction increases as the barrel wears.
     
  5. Michael Eichele

    Michael Eichele Well-Known Member

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    Often times due to improper cleaning, the barrel becomes more polished. This increases the surface area and subsequent friction. In addittion, as the throat wears and cracks, it grips the bullet. In this case, much of the increased friction is in the first inch of the barrel.

    M
     
  6. Mikecr

    Mikecr Well-Known Member

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    What is the objective of this frictional testing?
    What do you hope to gain in it?
    If one bullet/coating combo provides less friction(following friction coefficients of coatings or otherwise), what will that mean?

    I can coat your bullets in WS2, no problem.
    I don't coat bullets to reduce friction though(don't know why anyone would).
    I coat to manage fouling.
     
  7. Michael Courtney

    Michael Courtney Silver Member

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    Thanks for your insights.

    Managing fouling can be important to many shooters. In other applications, an increase in muzzle energy is more desirable. Our preliminary work suggests that many bullets lose 200-1000 ft-lbs of energy to barrel friction. For organizations that have already made large scale investments in specific cartridges, increasing powder capacity is not an economical option, and increasing energy by increasing powder capacity carries with it penalties of decreased barrel life, increased recoil, and increased noise. Reduced barrel friction will also increase the benefits of longer barrels where the pressure curve is pretty small, and friction robs most of the benefits of increased barrel length.
     
  8. Mikecr

    Mikecr Well-Known Member

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    So it sounds like your objective to increase energy without increasing capacity, powder amount, recoil, or noise, or reducing barrel life -while also extending gains from longer barrels –by reducing bullet/barrel friction..
    Have you really thought this through?
    Why do you think these things will result?
    Is there basis to date from friction coatings already in use?

    The only real gains I’ve heard of in this regard(velocity) is with sabots.
    But nothing there is free of course.
    We know that use of moly reduces MV(for a couple reasons).
    We know that reducing friction in itself drops peak pressure by widening the peak, with a bullet further down the bore by that point.
    And IMO barrel/bullet friction is not the cause of dropping velocity gain rates in longer barrels, but merely a matter of powder burn rates dropping, with pressures reducing, as applied to greater bore area of longer barrels.

    Basically, friction/sealing/expansive area are basic factors with our powder burn rates and resultant muzzle velocities. And the price of affecting these(and each affects the others) is likely self defeating to your objectives, and of no gain to long range hunters(who need to hit what they’re aiming at)..
    I don’t know, maybe the tactical bunch would buy into this kind of stuff.
    I can't imagine anyone here taking this seriously
     
  9. Michael Courtney

    Michael Courtney Silver Member

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    We have thought this out carefully.

    The next step is quantifying how much friction is reduced by a given coating. If energy loss to friction can be reduced from 200 ft-lbs to 100 ft-lbs in a given cartridge, then increasing the powder charge (or possibly using a different powder) should be able to increase the muzzle energy by 100 ft-lbs with the same peak pressure and cartridge. If energy loss can be reduced from 1000 ft-lbs to 500 ft-lbs then the energy should be able to be increased by 500 ft-lbs for the same bullet and cartridge and peak pressure.

    Why hasn't this already been done? I can think of several possibilities. Perhaps no one has had the tools to accurately quantify barrel friction with and without coatings. We have that now. Perhaps there are more commercial gains to be had in introducing new cartridges rather than making the old ones work better. I suspect that reliable gains in friction reduction through coatings require more control over barrel quality and cleaning than can be exercised by an ammunition supplier, so they are reluctant to load ammo much hotter lest a small percentage of pitted or rusty barrels lead to a lot of liability lawsuits.

    Another fact to consider is that barrel friction will be highly correlated with fouling. (What other than friction rubs the copper from the bullet?) Fouling is a challenge to quantify, but now friction can be accurately quantified. A coating that does the best job at reducing barrel friction will most likely also do the best job reducing barrel fouling because it will reduce the forces between barrel and bullet which are rubbing the copper from the bullet.

    We've worked a bit with sabots and the energy lost to friction with a saboted load can pretty easily be reduced to about 80 ft-lbs. However, maintaining the accuracy needed for reliable hits beyond 200 yards is much harder than with coated bullets. In addition, sabots are a custom deal in all but a few calibers.

    Is a 100 to 500 ft-lb gain enough to justify a given coating? It depends on the application. Some match shooters need to stretch the .308 Win or .223 Rem to longer distances, and it might be. I could certainly use 500 ft-lbs more in my long range rigs in 25-06, 6.5x284, and .300 Win Mag, and I'd much rather get the gain from a bullet coating than rebarreling.
     
  10. Mikecr

    Mikecr Well-Known Member

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    Yet:
    It's clear to me that you(and whomever 'we' are) haven't thought this out at all.
    It's been done for many decades and you need to at least review the results of it.
    With this you will have gained nothing(velocity wise) while using more powder(reducing barrel life) to counter reduced friction(which lowered MV), -that you 'think' will provide more energy and increase barrel life!
    And you could go faster powder to counter/take advantage of less friction, but faster powders are hotter powders which reduce barrel life. So nothing free there either(surprise)..
     
  11. Michael Courtney

    Michael Courtney Silver Member

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    Our review has revealed that most of the "results" are qualitative and anecdotal, along the lines of "the coating caused the barrel friction to be reduced which caused a reduction in muzzle velocity. I was able to increase the powder charge to return to the same muzzle velocity with no signs of excessive pressure."

    Please enlighten us by providing citations or web links if solid studies quantifying the friction reducing properties of the common coatings has already been done.

    Careful, quantitative studies often solve problems and open doors to possibilities that anecdotal and qualitative studies had missed.

    Did you miss the Norma study showing that moly coated bullets lead to increased barrel life at the same muzzle velocity? There's a difference between the real loss of barrel life that occurs going from a standard to a magnum cartridge and the theoretical loss of barrel life that might result from adding a few grains of a faster powder to gain some velocity in the same cartridge. You also seem to assume that only the powder and not the barrel friction contribute to barrel heating. The added erosion and heating from the extra powder may well be offset by the reduced erosion and heating from a significant reduction in barrel friction.
     
  12. LouBoyd

    LouBoyd Well-Known Member

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    Could you give a description of your method of measuring "average barrel friction"?
    Not all the details, just enough information so we can understand how you can separate the forces of bullet bore friction from the forces of the propellant gas on both the bullet and the barrel.
     
  13. Michael Courtney

    Michael Courtney Silver Member

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    Because of various non-disclosure agreements as well as applicable laws and regulations, we won't be able to discuss the details of the method for measuring barrel friction until we have secured approvals for public release. We're completing the process now of preparing the manuscript for for internal peer-reviews. After internal peer-reviews, it will be submitted for approval of public release. Best case, the method will be approved for public release in December 2011, but it could slip until January 2012.