B.C./Drop Report--MUST READ&COMMENT

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by RockZ, Feb 2, 2010.

  1. RockZ

    RockZ Well-Known Member

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    With a great interest in BC on the board these days I figure I would include a report I've recently discovered. THIS IS NOT A JOKE! IT IS REAL!
    After a bid of dicussion I will post a link to the full report. You may find it interesting.

    Here is an excerpt taken from the report on B.C. with some drop data included.
    Please comment and give me a BC for this bullet according to the data.
    Unfortunately the author did not give the exact environmental conditions.

    Here it is:

    "How long the bullet yaws depends on the bullet itself, the rifling twist and even the crown of
    the barrel. Some barrel/bullet/crown combinations result in a much shorter period of bullet yaw,
    something apparently impossible to predict. When it does happen, however,the bullet will shoot alot flatter than indicated in any computer model. A fine example is my .257 weatherby Vanguard Sporter.This rifle shoots 100-grain Barnes Triple Shock XBullets into tiny groups--and also shoots them much flatter than the bullet's listed BC indicates. The muzzle velocity of the rifle's best handload is right around 3,500 fps and when sighted in 2" high at 100yards, the little bullet is still around an inch high at 300yards when shot at typical western elevations of 4,000'-5,000' above sea level, and only 5" low at 400yards.This is alot flatter than any ballistic program suggests, even when higher elevation is "plugged" into the equation."

    So guys:

    A. Is the writer of this report claiming an impossible BC to purposely mislead the public for the purpose of selling more 100 grain Barnes Triple Shock XBullets ?

    B. Is he a novice and just not familiar with the method of properly zeroing a rifle and testing drops?

    C. Is he simply stating the results he got with his rifle with no other adjenda

    OR:

    D. Other

    PLEASE CHIME IN!
     
    Last edited: Feb 2, 2010
  2. sniperjwt

    sniperjwt Well-Known Member

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    well after running the numbers im on my way to buy all these bullets i can find. :D Ok not really but barnes list a BC of.397 for these bullets and from what i come up with a .900 BC is what you would need and it still would not match up perfectly. It would be 2.2 inches high at 100 1.1 inches high at 300 and 4.5 inches low at 400. Now i know the BC can be off a little bit but i think it is usually higher than the actual BC not way lower. I also could not tell you of the choices you provided which one is the most correct.

    Now if the guy cant read a tape measure or a pair of calipers then it might be pretty close with a bc of .400 2.6 high at 100 will give you 1.3 high at 300 and 5.6 low at 400 which this may be more the case because he may have just been guessing and not actually taking a measurement.
     

  3. J E Custom

    J E Custom Well-Known Member

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    It could be a case of "TALL TAILS"or simply the wrong velocity numbers.

    Some barrels shoot faster than others buy up to 100 ft/sec and this could skew
    the numbers.

    Not all high pressure loads show typical pressure signs.

    I think it is all of the above.(Wrong velocity,poor measurements,high pressure load,
    tall tails or maybe the wrong yardage numbers.

    It is hard to say how he came up with those numbers .

    Over the years I have heard many tall tails of how flat someones rifle shot and normally
    It was over estimating the yardage (A 500yard shot that was really under 300yards).

    I my self witnessed this with a well respected guide after making a good 600yrd + shot
    that he swore to all was over 900 yards. (Who was I to correct him in front of everyone)
    But I knew because I ranged it several times before and after the shot.(We did not have
    range finders back then) and there was some guessing and stepping off the distance.

    So I would say Don't Believe every thing you hear !

    J E CUSTOM
     
  4. MontanaRifleman

    MontanaRifleman Well-Known Member

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    These drops really aren't that far off the mark. If I run a .5 BC with an MV of 3500 @ 5000' elevation zeroed @ 320 yds I get

    100 - +2.6, 300 - +1.0, 400 - -5.6

    with a BC of .4 I get

    100 - +2.8, 300 - +1.0, 400 - - 6.0

    with a BC .4 and an MV of 3700 I get

    100 - +2.4, 300 - +0.9, 400, - -5.3

    Not a whole lot of difference between those and all very close to the bullets actual published BC.

    The data provided is much too general and just slightest mis reading at those short distances can result in huge calculated BC swings. Chrony's are not all that reliable and how consistant are the loads being used? There are a lot of possible varibles that could greatly affect a calculated BC at those short distances including maybe the possibility of pitch and yaw.

    Will be interested in reading the rest of the article but I think it will mostly be anecdotal based on info provided so far.

    -Mark
     
  5. Jamie6.5

    Jamie6.5 Well-Known Member

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    So the author is claiming that his particular gun/barrel/twist/crown combo consistently causes this particular Barnes bullet to "yaw" in a tail down, meplat up attitude? Causing it to maintain a flatter trajectory because it is "flying," achieving lift from said yaw? Every single time??

    I suppose it could be possible,...

    But I'm going to remain the skeptic about it.

    Now if a barrel maker comes along and claims (with documented proof) that they can engineer/build barrels that do this every time I might,...

    Naw, I still don't think so!
     
  6. bigngreen

    bigngreen Well-Known Member

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    Playing with JBM I don't have to change BC to get those numbers, just changing the scope hight will get it. I shoot with a scope hight of 2.2 so that is what I compared to.

    300yrd 0 in, 400yrds -7.3 in

    Now change the scope hight to 3in

    300yrd 1.6in, 400yrd -4.9 in

    I'm just getting the hang of ballistic calculators but you can really screw something up if your inputs aren't quite correct, and you then think you shooting a miricle bullet.
    I start looking for where I screwed up on my inputs when my drops don't come reasonably close to the predicted trajectory, so far I have found the problem to be me and my data not some miracle BC.
     
  7. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Bigngreen, scope hieght is another big consideration. when I played with that it dramatically changed things..

    Bottomline, I dont see anything all that unusual in the data provided.
     
  8. bigngreen

    bigngreen Well-Known Member

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    I kinda find it hard to try to make a BC claim with out shooting it out at distance. His BC may be very different if he would have shot it at 7-800 yrds. In close it seems that speed will mask BC but at distance your running on BC. I would think that the farther you shoot the less perfect your measurements can be and still be in the ball park also.
    I have made dozens of charts only to have them fail at 750 yrd not because of BC but because I failed to input correct data in my enviromentals or measurements.
     
  9. RockZ

    RockZ Well-Known Member

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    I got about .85 on my iPod ballistic
    MR
    There's a big difference between 2 and 2.6@100yds
     
  10. MontanaRifleman

    MontanaRifleman Well-Known Member

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    RockZ, How big was the group that determined this 2" @ 100yds? And the rest of the drops?

    A lot of room for error and variation in this kind of scenario. If you want to make any sort of reasonable conclusions you need more precise data and more of it at longer ranges. This simply does not tell you much. I have shot numerous sets of groups from 100 to 600 yds where not every set "fits" into the a particular BC or trajectory. Go out and actually try it some time. Shoot some 3 or even 5 shot groups at 100, 200, 300, 400, 500 yds and you will be lucky if any 3 sets of groups perfectly match a BC trajectory. Then go out and try it again the next day. I can just about guarantee you that your data for the two different days will not match with 1/2" consistantly. Especially with a sporter rifle.
     
    Last edited: Feb 2, 2010
  11. RockZ

    RockZ Well-Known Member

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    MR
    you are right about that
    but using the drops given and matching them more closely
    the BC seems very high
     
  12. 7 loader

    7 loader Well-Known Member

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    Im sorta new to this but a mv 3500 fps= to a velosity around 3284 fps and at 100 yds. At 300 yds the velosity is 2892 give or take. the drop at 300 yds is around 15 in, and 27 in at 400 yds. The bc may also be incorect. Acording to the math it is .42. I don't know but my math may be all wrong.gun)
     
  13. bigngreen

    bigngreen Well-Known Member

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    I was thinking about this and the question came to mind. Is figuring BC based on trajectory only taking into account the BC from the point where the bullet and scope are zeroed out? Should I be trying to look at it as total drop from the muzzle to range b and c to find a BC that isn't infuenced by scope hight or zero range and height?.
     
  14. MontanaRifleman

    MontanaRifleman Well-Known Member

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    On the surface this data seems to indicate a high BC. But within some very close variation or margins of error the BC could be quite "normal". It's like trying to measure a hair with a yardstick.