Question for 50 Cal shooters

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by J E Custom, Jun 11, 2010.

  1. J E Custom

    J E Custom Well-Known Member

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    I am interested in the performance of the 50 (.510) BMG after it goes Sub Sonic.

    I know that most bullets really lose there accuracy when this happens and was wondering
    if anyone had done any comparisons between lighter bullets and heavy bullets at sub sonic
    velocities.

    Question: Are the heaver bullets less effected by the transition to sub sonic or they
    essentially the same.

    The old Black powder rifles are capable of outstanding accuracy at long distance and most
    go sub sonic soon after they leave the bore.

    They usually use 500 to 600 grain bullets and the modern LR rifles use 250 to 400gr bullets
    at much higher velocities and with much better BCs.

    With the better 50 cal bullets(BCs over 1) and muzzle velocities over 2800 ft/sec they go
    through the transition at well over 2000 yards with 750 to 800 grain bullets.

    So I was wondering if heavy projectiles were less effected during Sub Sonic flight.

    All opinions are welcome but also anyone with facts and figures are what I need .

    J E CUSTOM
     
  2. LouBoyd

    LouBoyd Well-Known Member

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    I think you'll just have to try shooting them at very long range and see how they perform. I've shot both 750 and 800 Barnes solids at up to a mile from my 40" McBros single shot but at that range they're both well supersonic.

    Computer programs (McGyro and McTrag) can calculate the stability of spinning projectiles and the drag, but they don't calculate the difference in loss of spin and forward energy. They can't really calculate long range stability correctly.

    With sufficient initial velocity heavier VLD bullets will typically travel further before going transonic then lighter but faster VLD bullets. It's not obvious which bullet will be more accurate even up to the point where the lighter bullet goes transonic though wind deflection and velocity sensitivity for both can be calculated. Precession effects related to stability are generally too complex to calculate. Really, the only way to know for sure is to do shooting tests at those ranges with various bullets.

    Personally I don't attempt to shoot at distances which give transonic velocities. Sure, you can shoot transonic to at least twice as far transonic as supersonic, but the chance of obtaining decent accuracy (limited by wind deflection and muzzle velocity variation) becomes small rapidly after bullets become transonic even it the bullet does remain stable. Time of flight is a big part of both drop and wind deflection. Slow bullets simply cannot compare well for accuracy to supersonic bullets at ranges over a mile whehter they remain stable or not. For subsonic only shooting where the bullet has no stability problems practical hunting ranges can't be over about 600 yards for any known cartridge/bullet combination.. Sure, a heavy subsonic bullet can kill at over a mile, but it cannot be very accurate limited by wind deflection and muzzle velocity variation (usually the latter).

    It's practical to build shoulder fired rifles which can reach 2500 yards supersonic. The Cheytacs and similar can do it. They're still too wind sensitive to assure reliable hunting accuracy. 50 BMGs can't do as well. They have too much bore area to case capacity regardless of bullet selection. That is, low drag 50 cal bullets are too slow.
     

  3. ROBSTER

    ROBSTER Well-Known Member

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    Try jd jones @ ssk ind. He has the 510 whisper that sends 700 grain slugs down range @1050 or less to be truly suppressed.
    Robster
     
  4. britz

    britz Well-Known Member

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    at 1050 fps it is subsonic. The point is to stay below the speed of sound to avoid the transonic stage.
     
  5. Chas1

    Chas1 Well-Known Member

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    Robster, is it leaving the muzzle at 1050fps and if so any idea at what range it essentially runs out of gas?
     
  6. ROBSTER

    ROBSTER Well-Known Member

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    Chas,
    I`m not sure on the .510 I shoot a 338 whisper with 300smk`s sighted in at 200yds i`m 15 high at 100yds and 51 low at 300 yds at aprox 950 fps.Works great for woodchucks and coons.
    robster
     
  7. J E Custom

    J E Custom Well-Known Member

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    I guess what I am trying to find out is if your going to shoot out past the super sonic are
    the heaver bullets effected less because of mass.

    With all the talk about 2700 yard kills/hits it looks like it would be more likely with a heaver
    projectile. The MI Abrams battle tank was making hits in excess of 2 miles and I know/think
    the velocity is below the speed of sound at that distance.

    There is no hidden agenda just curious.

    When I can find a place to shoot far enough I will test it out my self unless someone comes
    up with real data.

    Thanks
    J E CUSTOM
     
    Last edited: Jun 12, 2010
  8. Chas1

    Chas1 Well-Known Member

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    Robster, thanks for responding...damn that's a lite load but neat.
     
  9. LouBoyd

    LouBoyd Well-Known Member

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  10. britz

    britz Well-Known Member

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    wouldn't a tank round be very very low drag due to the fact it is like a dart?

    Also, from what I hear the sniper record was admittedly not a one shot one hit deal.
     
  11. LouBoyd

    LouBoyd Well-Known Member

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    The M289 projectile certainly has many times more drag than a 800 grain Barnes solid 50 BMG bullet. On the other hand it has in the order of 400 times more kinetic energy (roughly 100 times from it's mass and four times more from from the velocity squared). The percentage of the penetrator's energy which is lost from drag per unit distance is tiny compared to the 50 BMG VLD bullet. This is a drawing of the now discontinued M829 projectile. There are newer models which give better performance but this is the only one I found a drawing for.
    [​IMG]


    Is a low ratio of shots per kill at long range a good thing? If so then it should be wonderful that carefully targeted MIRV ICBM could get around a million kills per shot at over 6000 miles.
     
    Last edited: Jun 12, 2010
  12. J E Custom

    J E Custom Well-Known Member

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  13. J E Custom

    J E Custom Well-Known Member

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    Up date;

    I just recently had a long conversation with a very knowledgeable person (Not that
    there are not any on this site) with tons of big bore experience and a barrel maker.

    After a very detailed explanation I understood the relationship between the larger
    projectiles and the smaller one.

    Hear is a layman's explanation. The larger / heaver projectile is less effected by any
    outside effects because of Mass. Therefore when it passes through the transonic
    it will exhibit the same characteristics of the lighter projectile but with less effect on
    it's POI.

    The same thing happens when loading large/ heavy projectiles when comparing the
    Standard deviation with lighter/smaller projectiles. It is fairly easy to get single digit
    SDs (02 to 09) with 400gr+ projectiles but very hard with 40grain projectiles because
    of all of the outside influences and inconsistencies.

    So I think I understand that In the case of projectiles that go's subsonic the larger the
    projectile, the less effected it will be even though it will not be as accurate as it would
    be it the supersonic environment it would be more likely to maintain it's trajectory and
    accuracy to some degree of consistency better than a small light projectile.

    This looks like a case where bigger is better if you are going to exceed a projectiles
    operating range.

    Comments and opinions are still welcome

    J E CUSTOM
     
  14. LouBoyd

    LouBoyd Well-Known Member

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    SD does go up with bullet weight for a given shape and material. For two objects of the same shape mass increases with the cube of the linear dimensions while frontal area increases with the square of the linear dimensions. But SD does not by itself tell anything about bullet stability. Even knowing the exact mass, velocity, bullet shape, spin rate, and atmosphere doesn't determine it's stability. How the mass is distrbuted internal to the bullet affects it's rotational inertia and center of gravity all of which affects stability.

    The above information may come from a great shooter and great barrel maker but what was in your post simply does not describe what makes a bullet stable or not.