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Thread: Question about Ballistic Coefficient

  1. #1
    Happy Camper hcpookie's Avatar
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    Default Question about Ballistic Coefficient

    Will the ballistic coefficient be altered if a bullet is ?bumped? down to a different size? For example, if I resize a .375 bullet down to .366, will the original published BC for the .375 still be valid?

    Sorry if this is a dumb question but I'm still getting my head wrapped around this topic.
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    Administrator pirate56's Avatar
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    I believe the BC is a factor of diameter, length, weight and shape. I have a book that explains it. I will look it up tonight.

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    Gunco Maniac sjohnson's Avatar
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    The BC will change, though not a lot unless the swaging process significantly alters ogive or other geometric characteristics of the bullet.

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    No Hope For Me 1biggun's Avatar
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    Any change in the bullet other than color will likely alter the BC. a good example is the differances between a 6.5mm and a 6.8mm bullet even though they are the same design the will be fairly differant. in your case bumping down the OD will likely give you a higher (better) BC. I have been studying this stuff a little lately trying to come up with a better long distance varmit round. Is this for your 9x39mm project???

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    tired of idiots vz58's Avatar
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    I second sjohnson and 1biggun, you will improve the BC by stretching the bullet.

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    Happy Camper hcpookie's Avatar
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    Quote Originally Posted by 1biggun
    Is this for your 9x39mm project???
    Perhaps


    I'm looking at the FMJ options and there aren't many. As in none. If this bullet swaging actually works, I'll be making FMJ bullets from scratch, or altering existing spire-point bullets. Nosler accu-tip bullets are the closest to FMJ and are my first choice, but they have exactly 2 weights that close to my target sizes. I bought a Lee resizing die, and it works. It stretches the bullet and makes tha ogive slightly less, and the cylinder is slightly longer.

    I'm sure it will improve, but I really don't want to compute the mass and sectional density and all of that stuff. The Speer book I have has the charts to compute energy is based on the BC and bullet weight. I can probably get the computation fairly close if I use velocity and bullet weight and go from there.

    It will be interesting to see if for example a 260 grain resized bullet performs vs. a 250 grain bullet that was not reformed.
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