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Subsonic?

Discussion in 'Caliber Corner' started by NavyMSU, Nov 4, 2011.


  1. NavyMSU

    NavyMSU
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    Okay, I get that it travels less than the speed of sound, but what is the advantage of a subsonic round?
     

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  2. Davegrave

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    Often sought after by people using silencers. The silencer will lessen the sound of the explosion, but if the round is traveling at super sonic speeds there's still the loud sonic boom.
     

  3. barth

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    Crap you beat me to it?!? LOL!
    Oh Well,

    To a lesser extent -
    In the past you might get reduced muzzle flash with sub sonic.
    But today's high tech rounds use low flash, fast burn, powder.
     
  4. NavyMSU

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    I assume lower velocity = less recoil? Do subsonics cost less? If so I could see them used at indoor ranges, but otherwise I dont see the appeal.
     
  5. NG VI

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    In service calibers subsonics tend to be the heavier, higher sectional density bullets. They tend to have higher momentum, and thus either deeper penetration or a greater expansion allowance for the same amount of penetration.

    Expansion retards penetration, but a heavier bullet in the same caliber has more momentum to shed, so it can afford to lose more penetration capability to wide expansion than a similar but lighter bullet before it stops penetrating deep enough.
     
    #5 NG VI, Nov 4, 2011
    Last edited: Dec 13, 2011
  6. ABNAK

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    Well put.
     
  7. NG VI

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    Thanks ABNAK. It felt circular though.


    Subsonic loads out of service calibers are rarely underpowered loads, they are usually just the loads for that caliber using a heavy bullet. And they aren't uncommon or something you will have to hunt for either, pretty much 147 in 9mm, 180 in .40, 200 or 230 in .45, and non-+P 185 .45 may or may not be under the sound barrier, depending on the load.
     
  8. NavyMSU

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    Momentum is a measure of velocity and mass. Greater mass and less velocity would balance against a 'sonic' round (higher velocity/lower mass), producing a similar force at impact and I would think lower velocity would reduce penetration but knock a fool on his ash.

    If it were higher density there would be less expansion and deeper penetration, but if you want penetration why not just hot load FMJ the fool?

    Unless you meant larger mass, lower density (more expansion). Now that would pack a punch!

    I didn't know subsonics tended to be larger - that's worth learning.

    I guess I just can't wrap my head around it. Long time shooter, but only recently interested in the ballistics.
     
  9. JimBianchi

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    In most of my 22LR guns, the subsonic ammo is NEARLY as accurate as match ammo at a fraction of the cost.

    CCI subsonic ammo is my favorite ammo and it will shoot one hole groups if I do my part.

    Remington subsonic ammo is also dirt cheap and very accurate.
     
  10. Jeff82

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    .22LR match ammo is usually always sub-sonic. Rounds that go through the sonic barrier undergo buffeting causing them to be slightly less consistent.
     
  11. NG VI

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    A heavier bullet will have a higher sectional density than a bullet of the same caliber that weighs less. It's the term for for the weight vs cross section of a bullet. And in service calibers, you can't gain enough velocity going with the lighter supersonic loads to equal the momentum you get with a heavier bullet.

    FMJ in a service caliber gets anywhere from 24-28" of penetration typically, which is much more than most people would like if the target is something like a medium sized animal in an uncontrolled, possibly crowded location. Most people loading a handgun for defense want at least a moderate amount of expansion out of the load they select, even if it isn't their top priority. Most people don't want penetration at the cost of every other factor involved with a bullet, or expansion at the cost of every other factor involved with ballistics.

    Modern heavyweight JHPs tend to be extremely well balanced and exhibit favorable recoil and blast characteristics compared to lighter bullets in the same caliber. Often times they shoot well in many guns. And most importantly, the difference between a light bullet+highest possible velocity for caliber load and a heavy bullet+moderate velocity load is really not as extreme for pistol rounds as you might think.

    In a heavy revolver or rifle cartridge, there is much more room for shenanigans, though the same basic ballistics rules apply to every platform.

    There's a lot of reading you should do, browse around a little bit, try not to spend too much time on articles or books that seem breathlessly exhuberant, most of the real experts out there come across as very level-headed and do a decent job giving examples and explaining not just that something works the way it does, but why.
     
  12. NavyMSU

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    Nice clarification: the larger bullets density via cross section... Now I get what you're saying.

    Thanks, excellent explanation. Any books you'd recommend?

    I'm a computer engineer and I took some very robust physics courses in undergrad 8 years ago and if they taught bullet ballistics instead of a 'car crashing into a wall', I probably would have paid more attention aced the class!
     
  13. Angry Fist

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  14. chasbo00

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    The speed of sound in air is mainly determined by the air's temperature. Here are some examples in feet per second (fps) and degrees Fahrenheit:

    95 Degrees 1154 fps
    68 Degrees 1126 fps
    32 Degrees 1087 fps
    05 Degrees 1057 fps

    What's revealing here is that lots of ammunition is subsonic, and not just those marketed as such.
     
    #14 chasbo00, Nov 5, 2011
    Last edited: Nov 5, 2011
  15. NavyMSU

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    Indeed. Earlier post hinted at that mentioning a 200gr or 230gr .45 would be subsonic.

    Guess its just a marketing thing.

    I guess if you know you want subsonic, you just have to understand this basic info, everybody else probably doesn't care since their ammo is likely subsonic anyways.
     
  16. Darkangel1846

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    big honken slow moven rounds...sound suppression, flying ashtrays, big holes:wavey:
     
  17. Numismatist

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    If you fire a 9mm Subsonic (without any silencer or other additional apparatus), can you actually hear a noteiceable difference from normal rounds? say in a G26 for example, or is it indiscernable fmro the sound standpoint.
     
  18. ADK_40GLKr

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    (from http://www.thegunzone.com/buzzwords.html )
    "First, ya gotta know that subsonic simply means "beneath the speed of sound," which figure can be obtained (it varies with ambient temperature and humidity) at the Speed of Sound Calculator http://www.sengpielaudio.com/calculator-speedsound.htm website. (For the purposes of this monograph, a figure of 1117 feet per second will be utilized, given input parameters of standard atmospheric pressure, 59° Fahrenheit and 10% humidity.)

    "Within the firearms community, the "subsonic" nomenclature originally was a convenient description to differentiate the heavyweight 147-grain 9 X 19mm round (at a nominal 950-1000 fps) from the conventional "supersonic" 90-to-124 grain rounds in that chambering, turning up muzzle velocities in the 1150-1400 fps range."
     
  19. NG VI

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    I just re-read this thread, and decided to multiply typical bullet weights by typical advertised speeds, and I was actually wrong earlier, in the .40 and 9mm, the lighter middle weights like the 124 and 155 generate pretty close to the same amount of momentum as the 147 and 180s.

    But the lighter bullets do slow down faster than the heavies, probably not a very significant factor in defensive shooting, and they still do have the mechanical disadvantage of less sectional density and less material to work with for expansion+penetration.
     
  20. NG VI

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    I pretty just read the living crap out of whatever ballistics information I could a few years ago when I was really big into it, and it just seems like the bulk of the dependable information out there that was current showed our generation of heavyweight JHPs doing everything the lighter weight bullets do more reliably and often to higher degrees.

    The ATK Federal/Speer ammunition workshops are extremely helpful to see what the typical bullets of today will do in a variety of situations, and compares them to one another directly, with repeatable tests. You can find them very easily, just google something like ATK ammunition workshop, and they'll be listed by date and location.