ojive question

Discussion in 'ELR, Ballistics & Bullets Board' started by bigstick6017555, Nov 12, 2018.

  1. bigstick6017555

    bigstick6017555

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    I am thinking of trying a custom bullet, i have a 6mm br Mark Chanlyn 4 groove 20" barrel 1 in 13 twist, 100-200 yd shooting. Of my flat base, bullet weight choices i have all are a tangent, 6/9 (secant) double radius, 8 single radius, or 15 single radius. what are the advantages of the double or single radius's, and the amounts of radius
     
  2. Tim s

    Tim s

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    As much as anything, less wind impact. Some of the better 6’s we see around here are either straight 8’s or 7/11’s .
     
  3. boltfluter

    boltfluter Gold $$ Contributor

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    In theory double radius and bigger radius should have a better BC. Tangent radius is generally easier to tune for maximum accuracy. But, both can be extremely accurate. Have fun! :D:D

    Paul
     
  4. bigstick6017555

    bigstick6017555

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    thanks guys, fun indeed:)
     
  5. Ballisticboy

    Ballisticboy

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    In theory, based on extensive wind tunnel tests, a close to 0.5 secant ogive (secant ogive radius twice that of the tangent ogive radius) has the lowest supersonic drag. There are other specialised shapes which in theory have lower drag coefficients but you will probably never notice the difference. Also don't forget that for a given fixed nose length you can get some drag reduction by introducing a small hemispherical meplat.
    Don't get hung up on minimising your zero yaw drag. If your super low drag nose causes some bullet yaw it will soon wipe out any advantages of the low drag nose. You are after the lowest total drag for your bullets, i.e. zero and induced yaw drag.
     
  6. damoncali

    damoncali Gold $$ Contributor

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    It’s not a simple question to answer. You need to look at the overall bullet design, not just the radius of the ogive.

    For example, if you have an optimal drag nose like the 0.5 Rt/R (which is a pretty pointy VLD like design), you give up a little weight over a less aggressive secant ogive (due to a lower volume nose). As a result, you can wind up with a lower BC even though the shape is more efficient.

    Very, very generally (probably too generally), long and skinny = low drag. Short and stubby = well behaved and accurate.
     

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