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Thread: 500 S&W Heavyweight stability (Help with understanding)

  1. #1
    Boolit Man

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    500 S&W Heavyweight stability (Help with understanding)

    Hello everyone,

    I am having trouble wrapping my head around the many statements I have read about the 700 grain Boolits being unstable in the 4" or (shorter) barreled guns. I have looked at many stability calculators and they indicate that the bullets should be very stable but that does not coincide with many of the results discussed on the threads I was able to find. I assume the trial and error of this inspired John Ross to develop his Performance Center version of the X Frame along with the long range shooting aspect.

    Posted below are pictures of the results I have obtained of the calculators.

    You will note that i used 10 degrees fahrenheit for temp and 30.5 hg or -100' for the pressure to take things to the least stable solution possible. Also I chose an intentionally slow velocity 500 FPS with the standard twist of 18.75. Bullet is 700 grains and 1.33 " in length.

    Here is JBM's calculator.

    Click image for larger version. 

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    Here is Berger's.

    Click image for larger version. 

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    Here is a excel spreadsheet linked by Accurate shooter.

    Click image for larger version. 

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    And last but not least is a twist calculator from TMT Enterprises where all the fields were filled in and the button under Muzzle velocity was pushed to calculate the optimum velocity. Note the velocity is easily achieved by the shorter guns.

    Click image for larger version. 

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    Now with these calculators indicating the bullet should be stable why aren't most people getting that as a result? Aside from the fitment to the bore/throat and alloy/powder choices what other factors could cause a theoretically stable bullet to fly poorly?

    My theory is that the longer projectiles along with a good amount of recoil contribute to the upsetting/tipping of the bullet while it is leaving the muzzle at the slower speeds creating a fairly radical yaw that creates stability issues that the spin is unable to correct.

    I'm interested in your thoughts but I would like to keep this as a learning exercise for the sake of learning and the usability and practicality of this are very secondary.


    Thank you
    BHill

  2. #2
    Boolit Master maxreloader's Avatar
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    never heard this. very interesting.
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  3. #3
    Boolit Man

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    Just wanted to run this back up to the top and see if someone would like to take a stab at it.


    Thanks

  4. #4
    Boolit Master John Ross's Avatar
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    Quote Originally Posted by BHill View Post
    Hello everyone,

    I am having trouble wrapping my head around the many statements I have read about the 700 grain Boolits being unstable in the 4" or (shorter) barreled guns. I have looked at many stability calculators and they indicate that the bullets should be very stable but that does not coincide with many of the results discussed on the threads I was able to find. I assume the trial and error of this inspired John Ross to develop his Performance Center version of the X Frame along with the long range shooting aspect.

    SNIP

    My theory is that the longer projectiles along with a good amount of recoil contribute to the upsetting/tipping of the bullet while it is leaving the muzzle at the slower speeds creating a fairly radical yaw that creates stability issues that the spin is unable to correct.
    I think this may be part of the reason. A fifty pound .500 might stabilize a 700 grain bullet @ 900FPS because muzzle flip would be almost nonexistent, while in a 4" gun it is severe.

    However, I also wonder what formula(s) these various people are using. There is a DOS program for interior ballistics that I've used since 1989 (sort of a poor man's Quickload) that gives twist requirements along with the output.

    I just asked it what load to use for a 725 grain bullet, 1.4" long, at a pressure under 35,000 PSI in the .500. It says to use 22.3 grains WC680 for a velocity of 914 FPS and pressure of 32,500 PSI. It also says I need a twist of 1:9.7 or faster to stabilize this load.

    The guy who wrote that program was on to something...

    JR
    Last edited by John Ross; 01-09-2018 at 10:10 AM.
    JR--the .500 specialist

  5. #5
    Boolit Master Electric88's Avatar
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    Interesting. My best guess (and it is a hunch, so take it with a grain of salt) would have been that with a heavier slug, you would need more barrel length to get that slug spinning fast enough to stay stable. Offhand, I don't know that there are faster twist rates in the shorter guns to make up for that. That's just where my mind goes though, that you either need a faster twist rate in a shorter barrel to get the heavy boolit spinning, or more length to get it spinning.

  6. #6
    Boolit Master

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    Theories and thoughts are fine and dandy.....load some up and see what happens.
    The 250 grain boolits I tried in a 357 magnum didn't shoot worth beans...but I gave it an honest test.

    500 S&W Loads ? I can't help you there...maybe someone with access to Quick Loads could help.
    Gary
    Last edited by gwpercle; 01-09-2018 at 02:58 PM. Reason: spelling
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  7. #7
    Boolit Man

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    Quote Originally Posted by gwpercle View Post
    Theories and thoughts are fine and dandy.....load some up and see what happens.

    Gary
    Absolutely will do just that. Waiting on the group buy to finish as that is the whole reason to purchase it! Probably build a bullet trap to recover these as the lead bill could add up fast!

    I find this an interesting problem as the ballistic calculators have proved very good in the past, on other projects, but the actual users report very different results for the most part in this case.

    Thank you to everyone replying as this isn't a slam dunk.


    Mr. Ross,

    The program you have wouldn't happen to be the "McGyro" would it? I found a web version of it derived from the DOS program written in the late 80's. Link just below. However it doesn't end up with near the twist yours did so your guy may have been on to something. Intentional or not

    http://www.geoffrey-kolbe.com/barrel_twist.htm

  8. #8
    Boolit Master John Ross's Avatar
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    Quote Originally Posted by BHill View Post
    Mr. Ross,

    The program you have wouldn't happen to be the "McGyro" would it? I found a web version of it derived from the DOS program written in the late 80's. Link just below. However it doesn't end up with near the twist yours did so your guy may have been on to something. Intentional or not

    http://www.geoffrey-kolbe.com/barrel_twist.htm
    No, Suggest-a-Load by Lawrence Sayre.
    JR--the .500 specialist

  9. #9
    Boolit Man

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    Thank you

  10. #10
    Boolit Master

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    The hypothesis I would submit is the following:

    You are using Miller Stability, which at the end of the day, is nothing more than a model. It might be a really, really good model for 5.56 nato and tell you exactly what is going ot happen before the first shot is fired. Ditto for any similar cartridge to the military standard, as I believe Miller was developed for the military, yes? Thus for example, most bottleneck rifle cartridges would model very well.

    This may not apply so well to pistol. In fact, if you want even more fun, model the 460 S&W. You can get results of stability >12, yet the bullet will tumble.

    ----------------------

    Last thing I will suggest is that powder is NOT taken into account in these models. Therefore, the model doens't care if you spin your bullet up to 1200 fps using H110 or AA#9, the stability is the same. Yet, at least for MY gun, I can get round holes with H110, and ovals with AA#9, and that is with a bullet I GUARANTEE is stable at that speed, and nicely accurate with H110 to boot.

    In short, I question the model.





    ----------------

    I strongly doubt the recoil model, because the barrel flip velocity is going to be HUGELY slower than bullet speed across one inch of bearing surface. I'd want to see a calculation of the actual flip during bullet exit.

  11. #11
    Boolit Master John Ross's Avatar
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    Quote Originally Posted by Whiterabbit View Post
    I strongly doubt the recoil model, because the barrel flip velocity is going to be HUGELY slower than bullet speed across one inch of bearing surface. I'd want to see a calculation of the actual flip during bullet exit.
    An easy way to test that would be to shoot 700 grain heavy loads in a 3" .500, then load the ammo down to the same velocity in a 10" .500 and compare.
    JR--the .500 specialist

  12. #12
    Boolit Master

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    I wouldn’t trust the results. I would though if you put an accellerometer on the muzzle and charted that data vs speed vs keyholing. If you are right, there will be a transition and then reliable keyhole region.

  13. #13
    Boolit Master

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    A lot of folks don't seem to understand shooting heavy boolits in a levergun with a 1:38 twist and when you try and tell them they need twist for stability, and they are wanting to lob a 300+gr boolit at 1,000fps, well, they get plain out annoyed when you try to explain why it is a pointless waste of time trying to do what they are wanting to do. This thread bears that theory out perfectly. On paper it works, in the real world, blah...
    Got a .22 .30 .32 .357 .38 .40 .41 .44 .45 .480 or .500 S&W cylinder that needs throat reaming? 9mm, 10mm/40S&W, 45 ACP pistol barrel that won't "plunk" your handloads? Shoot me a PM! Also on Facebook: https://www.facebook.com/Cylinderhone-756429174391912/

  14. #14
    Boolit Man

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    Quote Originally Posted by DougGuy View Post
    A lot of folks don't seem to understand shooting heavy boolits in a levergun with a 1:38 twist and when you try and tell them they need twist for stability, and they are wanting to lob a 300+gr boolit at 1,000fps, well, they get plain out annoyed when you try to explain why it is a pointless waste of time trying to do what they are wanting to do. This thread bears that theory out perfectly. On paper it works, in the real world, blah...
    The difference in this case is the stability calculators say that this would be unstable so theory and real world agree in .44 cal and just marginal with .45 caliber.

  15. #15
    Boolit Man

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    Quote Originally Posted by Whiterabbit View Post
    The hypothesis I would submit is the following:

    You are using Miller Stability, which at the end of the day, is nothing more than a model. It might be a really, really good model for 5.56 nato and tell you exactly what is going ot happen before the first shot is fired. Ditto for any similar cartridge to the military standard, as I believe Miller was developed for the military, yes? Thus for example, most bottleneck rifle cartridges would model very well.

    I agree that most of the calculators are using either Miller's improved Greenhill formula or a derivative close to it. However I stumbled across the below that appears to take some additional information in to account and shows it to be much lower than the others however it still indicates it "should" be stable.

    Click image for larger version. 

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    This may not apply so well to pistol. In fact, if you want even more fun, model the 460 S&W. You can get results of stability >12, yet the bullet will tumble.

    I don't have access to one but would be willing to use a donor for a year or two for testing


    ----------------------

    Last thing I will suggest is that powder is NOT taken into account in these models. Therefore, the model doens't care if you spin your bullet up to 1200 fps using H110 or AA#9, the stability is the same. Yet, at least for MY gun, I can get round holes with H110, and ovals with AA#9, and that is with a bullet I GUARANTEE is stable at that speed, and nicely accurate with H110 to boot.

    In short, I question the model.

    I agree the models do not look at every parameter that could influence bullet stability that was why I mentioned them in the original post. The many different outcomes we receive with seemingly benign/parallel changes is what makes our hobby so frustrating/much fun.





    ----------------

    I strongly doubt the recoil model, because the barrel flip velocity is going to be HUGELY slower than bullet speed across one inch of bearing surface. I'd want to see a calculation of the actual flip during bullet exit.

    I understand your doubts as that is where I started but then started thinking about how much mass there was and the potential leverage it would have at 1.3" hanging out of the barrel to start the tipping upon barrel vertical acceleration. At that point the high pressure gases would be hitting the base at an angle and could create additional disruption. I know this is speculative at best and pulling it out of my nether regions (likely) at worst.

    Thank you for taking the time to consider this as I know in the end we may never know. I just can't leave"it just is" alone.


    I will test things out in my gun with a large number of powders under the following conditions.

    1. Me/partner shooting rested
    2. Me shooting with barrel holding a 10#weight on barrel and rested on breakaway rest.
    3. Shooting in a ransom rest

    Loads will consist of at least 9 different powders with a very wide burn rate and energy content at pressure levels of the following.

    20,000 psi
    25,000 psi
    30,000 psi
    35,000 psi

    I'll make a determination at the end of that test whether or not to go higher or not based on how my hand feels and if the Ransom rest is still in one piece. I would be open to suggestions from anyone in the testing progress. Primary purpose would be to see if they are stable and secondary purpose is to determine accuracy. 700 grain bullet sideways will still penetrate I'm guessing.
    Last edited by BHill; 01-11-2018 at 02:21 PM. Reason: Fixed colors

  16. #16
    Boolit Master

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    If the primary purpose is to test stability, then you're doing nothing more than an exhaustive load development. I'm sure that with so many variables under test, you will be able to settle on a great load, tumble or no. Sounds like alot of good time burning powder.

    But that's an independent post compared to the topic. The topic implication is that such a study should be used (goal) to validate the stability model. But I think we already have enough evidence to suggest that the model does not represent the real world.

    Unlike dems and climate change models, when I don't see the real world line up with the model, I debunk the model and seek a better one (if I even need a model!)

    Anyway, good luck to you. Fun discussion. For what it is worth, it mirrors my own work in 2010 when I burned a couple thousand 460S&W rounds trying to figure out why my performance was no good compared to stability models. I too ended up simply rolling through an exhaustive load development and have a load that shoots gangbusters at 100 yards as a result. Without reliance on modeling.

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