Are you thinking of BC the wrong way?

Discussion in 'ELR, Ballistics & Bullets Board' started by DocUSMCRetired, May 6, 2017.

  1. Esoteric Junkie

    Esoteric Junkie Silver $$ Contributor

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    Scott,
    You hit the nail on the head!!!! Many people are chasing BC and not precision first followed by accuracy (placing the group on target). I would much rather have a lower BC projectile that groups and holds better elevation than a higher BC bullet, regardless of construction, that does not perform as well. BC is only one part of the equation.

    I think we are seeing a proliferation of turned solid projectiles, for larger ELR calibers, due to the limited availability of good lead core jacketed projectile options in .375-510". Once someone figures out how to draw a long concentric jacket that is suitable for heavy .375-.510" projectiles we will see a total switch to lead core jacketed bullets. Unfortunately, there are not many, if any, suitable ELR lead core jacketed projectiles in calibers larger than .338".

    EJ
     
  2. Ballisticboy

    Ballisticboy

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    Scott, EJ you are both correct in that BC is in practice of little use when you are out shooting. You could argue that a high BC bullet with the same precision as a low BC bullet may give better accuracy due to the lower cross wind drift and the slightly flatter trajectory but there are plenty of other factors which will have more affect than BC. You are only really going to use BC when you are trying to calculate trajectories which of course is what it was invented for. The main use for trajectory calculations is in fire control computers and I don't know of many rifle shooters who use one of those while shooting.
    But, even for trajectory calculation, BC has limitations in that, unless your bullet happens to be exactly the same shape as the reference projectile, you will need multiple BC values as no two shapes will have the same Cd/ Mach number drag curve shape. Over limited ranges and speed regimes this will not be a problem for most people as the accuracy of the results will be sufficient for many purposes, but as ranges increase it will become a problem. This is why, in the large calibre artillery ballistics world, BCs have not been used for about the last 50 years. It was getting to the point that you needed almost as many BC values for a trajectory as points in a specialised Cd/Mach number curve produced specifically for the shell in question. The widespread use of computers made the calculation of trajectories much quicker and easier. Also, using a Cd/Mach number curve, along with the shell weight and reference diameter, meant it is easier to see the effects of each individual parameter on the trajectory making it easier to produce error budgets. And if you are using a modified point mass model (used in most fire control systems) as opposed to a point mass model you are going to need a whole lot more input than just a simple BC or Cd/Mach number curve.
    The down side with using Cd/Mach number curves is that you need a different one for each bullet/shell design. You may also need different curves for the same bullet/shell design fired from different guns or even for the same bullet/shell design fired from the same gun but with the bullet/shell made in different countries.
    You should remember that the BC idea was created to simplify the calculation of trajectories in the days before computers.
     
  3. chromatica

    chromatica

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    Hi Alan,

    So do your bullets closely follow the G7 drag profile, or have you generated another standard?
     
  4. Papa Charlie

    Papa Charlie

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    I for one, would like to see a standard format that all manufacturers were to follow. What that is, I am not sure, but I am sure that there are more educated people that can come up with a standard that actually provides the details to compare different bullets from different manufactures. This would also require a standardization of testing, measuring and calculating the information that is provided to their customers.
    If this were any other industry, there would be stricter standards applied.
     
  5. mikecr

    mikecr

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    If this were a regulated industry your notion would apply. But this is merely free market.
     
  6. brians356

    brians356 Gold $$ Contributor

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    Sure, if all you want is a repeatable holdover for a particular range. What if you are seeking the flattest trajectory? You'd have to complete that process for many bullets, absent some published coefficient, to decide which one has the best ballistics at a particular range. There is value in having bullet BCs calculated and expressed uniformly across manufacturers so that a reasonably small number of candidate bullets may be preselected for detailed evaluation.
    -
     
  7. Berger.Fan222

    Berger.Fan222

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    The 50 caliber AMAX seems to be doing OK. It now accounts for 3 of the 4 longest confirmed sniper kills on record.
     
  8. DocUSMCRetired

    DocUSMCRetired

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    Not getting in to details in any way shape or form. This information is simply incorrect.
     
    JLT likes this.
  9. brians356

    brians356 Gold $$ Contributor

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    Thanks. The purported existence of an accessible official "confirmed sniper kill" record book failed my sniff test.
    -
     
  10. Esoteric Junkie

    Esoteric Junkie Silver $$ Contributor

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    Doc,
    Agreed!!!
    EJ

     

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