ICAO or Army BCs data ??

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Gustavo, Jun 27, 2005.

  1. Gustavo

    Gustavo Writers Guild

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    To produce accurate results, we all know that the atmposhere used shoulod be ICAO or Army (Standard), but we must couple the correct BC for the conditions. That is to match the BC to the conditions used.

    So, does anyone know how to find the model used by the bullets manufacturers when they publish their BCs values?? In short, how do we know if they are ICAO or Army based??
     
  2. abinok

    abinok Writers Guild

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    Sierra uses Metro for theirs. Im not sure about the others, and im not sure they all use the same one. Lost river ballistics for instance speciffically uses a different atmospheric standard. This would make their BC's appear higher than their competitors... provided you didn't know better. You could get a .6bc out of a pistol bullet if you could do your "testing and measuring" at a high enough altitude/low air pressure.


    smacks forehead repeatidly....gotta edit these before posting
     

  3. sierra22

    sierra22 Well-Known Member

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    Mostly army - better for advertisement as it gives higher bc.

    The Army Standard Metro atmosphere, now used only in ballistics, defines sea-level conditions as 750.000 mmHg of pressure (29.5275 inHg, 99.9918 kPa), 59 °F (15 °C), and 78% humidity. (Ref: U.S. Army Ballistic Research Laboratory, U.S. Army Aberdeen Proving Ground)

    source: http://en.wikipedia.org/wiki/Standard_temperature_and_pressure

    How's the shooting in Argentina?
     
  4. Mikecr

    Mikecr Well-Known Member

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    According to Lija, standard Metro conditions are used by Sierra and Hornady bullets. Speer Bullets and Nosler Bullets have used the International Civil Aviation Organization, (ICAO),
     
  5. JBM

    JBM Well-Known Member

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    [ QUOTE ]
    You could get a .6bc out of a pistol bullet if you could do your "testing and measuring" at a high enough altitude/low air pressure.

    [/ QUOTE ]

    I don't understand this at all. When measuring the BC, the density is not part of the BC -- it is a separate term. The only question is how different are the densities and mach numbers for the two different standards. At sea level, there is about 1% difference, less than the accuracy of the measured BC.
     
  6. Mikecr

    Mikecr Well-Known Member

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    There isn't alot of difference between the SL standards. But I believe the idea expressed with the pistol bullet related to those bullet makers who imply BC without regard to appples/apples conditions.
    For example, there is nothing preventing Berger from reporting local BC obtained at 5000' and Mach3(without mention of that). We would buy their bullets assuming initially that BC was obtained under std SL conditions, and seeing what appears as an advantage. Afterall, Berger does not provide any basis that I'm aware of for their numbers. Not even mach#.
    There are alot of bullets to choose from, and BC is very important at long range. Unfortunately, there isn't an independant body to report BC based on a single standard. Except that published from the gov't(.308s).
     
  7. brian b

    brian b Well-Known Member

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    Gustavo,
    this is very interesting , but when it comes to reality you can sort through some of this fecal matter by just shooting through your chronograph at various ranges and use a good ballistic program (Sierra,xbal etc).
    if you are really trying to figure out what the military is doing. J-Hole,ICAO,or the Army aint tellin you or me the truth (National Security).
    spend a day or two at the range with a good Chronograph and you can have your answers.
    B
    p.s.please use an oehler (chronograph)to save un expected drama at the range.
     
  8. abinok

    abinok Writers Guild

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    [ QUOTE ]
    But I believe the idea expressed with the pistol bullet related to those bullet makers who imply BC without regard to appples/apples conditions.

    [/ QUOTE ]
    exactly what i was going for...
     
  9. Gustavo

    Gustavo Writers Guild

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    First of all, thanks for the many answers!

    Second, shooting and hunting in Argentina is simply fantastic!! We have many options to (for a price of course) but mostly we can go from the Pampas to Patagonia...very wild and somewhat unspoiled terrain. Also a perfect scenario for LRH

    Take for example a BC of .400 (Army) if we convert it to ICAO the number goes down to .393 and now we can see that a long range the differences will show up very neatly so my original question.

    Of course taking velocity readings will solve the issue to some extent, at least we can have a BC under actual firing conditions but it's not very practical...

    In short, please correct me, only some companies acknowledge the atmosphere they used to compute BCs isn't it?

    tks!