true B.C s

Discussion in 'Long Range Hunting & Shooting' started by 333nontyp, Mar 30, 2009.

  1. 333nontyp

    333nontyp Member

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    Someone posted a true ballistic website for all bullets, just wondering if anyone remebers it thanks. I was told that the b.c.s from barnes and berger r not 100% true .
     
  2. Michael Eichele

    Michael Eichele Well-Known Member

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    This is a very complicated subject. More than most would realize. The truth is that Barnes and Berger have BC's based on tests done in their labs using their equipment just like ANY other bullet manufacture. Most manufacturers published BC's are close enough to get you on paper at LR but not neccesarily in the X ring.

    This is where it gets complicated. The reason you cannot get the same results as the manufactures is because youre not using their rifles. Your not using their loads. MANY factors go into a real BC and they will be different from rifle to rifle.

    Some factors but not limited to are:

    Bore quality, stability factor (which is related to the twist rate AND velocity AND bullet demensions), twist rate, groove number, velocity, bullet design, bullet construction, bullet runout, bullet defects and more. I didnt mention air density because after we find our true BC in the real world with our equipment, this number becomes a baseline or mathematical constant for our calculations. The BC will change from day to day in different air but the number we use to get accurate ballistics stays constant.

    It is impossible to have a website that lists the true BC of any bullet.

    Clear as mud right?
     

  3. J E Custom

    J E Custom Well-Known Member

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    Very good explanation Meichele !!!!!

    I feel the only way to get true BCs of a bullet is to shoot them at 100,200,300,400,500and600
    yards and if you can shoot 1000yds it will give you a good base line.

    Living at sea level as I do, every place I hunt is higher so it is the only way I trust the BCs.

    Even the bullet manufactures are at a higher altitude when they calculate BCs than I am.

    And when I hunt at 10,000 to 12,000ft the adjustments made starting with my base line
    are very close.

    J E CUSTOM
     
  4. 333nontyp

    333nontyp Member

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    thanks i appreciate the info , ill pm for the info thanks
     
  5. 333nontyp

    333nontyp Member

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    i live at 2200 , and when sheep hunting iam at 7000 aprx were the air is less dense , also some of the companies calculate their b.c.s at 100 or 300 yard values .
     
  6. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Hey guys,

    Can't speak for all, but I assure you that most manufacturers try to give the most accurate BC values they possibly can. But, as has been mentioned here already, these values are subject to a wide range of influences that most shooters aren't even aware of. Atmospherics do most definitely affect the measured BC, and it's worth remembering that those of your particular shooting situation vary from those of the BC derived under "Standard" conditions. Most bullet makers have to determine their BCs and then correct that data back to standard, so that they're comparing apples to apples with the rest of the industry.

    There are a number of ways to estimate a BC, but the only real way to know is to measure it; time-of-flight firing. This may be done via chronographs or doppler radar, but it's the only way to truly measure a bullet's BC. Against that, we still have some makers using things like calculated (estimated) BCs based on shape. I know that both Berger and Sierra have done (and do) this type of firing. I'm sure that some of the others do as well, but these are the only two that I've personally been involved with and can say with a personal certainty.

    Bottom line, BCs are an excellent way to evaluate one bullet against another, but the values shown in the literature must be corrected to your shooting situation to give you a chance at producing an accurate trajectory in a computer program. Do this, and you should see accurate results in the field. If you don't, you'll have problems and the BCs won't seem to fit what you're seeing in your own shooting. Remember, "Garbage In, Garbage Out," is true with any program. Lengthy topic that I'm sure we're not going to completely flesh out in a few sentences here, but there are some decent books out there, such as the classic "Hatcher's Notebook" (it's on everybody's bench, right?). Bryan Litz has one in the works right now that should become a standard for anyone looking for answers to this sort of question.

    Kevin Thomas
    Berger Bullets
     
  7. Michael Eichele

    Michael Eichele Well-Known Member

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    Well put.

    This is exactly why I use the 2 chrono method. One at 15' and one at 900'. Taking into account ALL atmosperic conditions is very critical here.
     
  8. 333nontyp

    333nontyp Member

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    thanks for the info , just wondering when a guy is computing data for longrange turret like from kenton ind. , is it okay to use the b.c.s from the manufactor . i was wondering if anyone has experience with just using the bullets manufactors data ,thanks
     
  9. Michael Eichele

    Michael Eichele Well-Known Member

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    Personaly I wouldnt. They are usually close and you could get away with it. Between any BC differences and atmosperic changes, you could be off enough to make a less than perfect shot. The problem with these preset knobs is that with air density changes and velocity changes from hot to cold temps you would be better off dialing in MOA's or Mils based on the current situation based on your targeting software.
     
  10. jwp475

    jwp475 Well-Known Member

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    Spot on as usual..
     
  11. Sharpstick

    Sharpstick Active Member

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    I prefer a preset turret because the majority of the the time it is correct. Generally if I go up a few thousand feet in elevation, the temps are lower and those 2 have offsetting effects, if I go down it works the other way. When I do need to take off or add a couple clicks due to atmosphere or incline, it's still simple to do with a yardage marked turret. If I hunt near sea level, it takes 30 seconds to put on my extra dial before the trip.

    The speed and simplicity of just dialing the yardage with no charts for 80% - 90% of my shots makes a yardage marked dial the best choice for me. Since I can still adjust a few clicks if the situation does warrant digging out the chart or the IPOD, I don't feel like I give anything up.

    Of course knowing how much to dial is more important than what method.