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Thread: Cast Bullet Ballistic Coefficent Table

  1. #21
    Boolit Master Marlin Junky's Avatar
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    The major problem with getting an accurate B.C. from "Precision Ballistic Coefficient Estimator" is that it doesn't consider Secant Ogives (on boolits) and will default to what looks like a Tangent Ogive if you try to insert the true "Ogive Radius in Nose Diameters" (for Secant Ogives).

    MJ

  2. #22
    Boolit Master

    Tom Myers's Avatar
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    Quote Originally Posted by Marlin Junky View Post
    The major problem with getting an accurate B.C. from "Precision Ballistic Coefficient Estimator" is that it doesn't consider Secant Ogives (on boolits) and will default to what looks like a Tangent Ogive if you try to insert the true "Ogive Radius in Nose Diameters" (for Secant Ogives).

    MJ
    Your are right. The site is not equipped to handle a Secant Ogive nose profile. Although it is possible to calculate a secant ogive value with three separate diameters on the ogive, the diameter values and the linear distances from the base of the ogive to those diameters must be precise to within 1,000 of an inch to obtain any degree of accuracy. I managed to set up an adjustable jig that could position the bullet and calipers so that accurate measurements could be made to determine a Secant Ogive Radius but that was not adaptable to a website application.

    One thing that you can do is, if you know for sure the actual secant ogive radius in nose calibers, is to increase the entry value in the ogive or nose length field in small increments until the calculated ogive radius matches your secant radius.

    This will work up to a point. As the angle at the junction of the secant ogive and the base increases beyond 4 to 6 degrees, the increasing Secant Ogive Value does not continue increasing the ACTUAL ballistic coefficient value of the bullet. So this is problematic in that, without some fairly intensive math algorithms to determine that angle, one does not know precisely where to quit increasing the nose length.

    An estimate is that if you increase the nose length on the calculator beyond 25%, the 4-6% limit will be passed and, approximately, a maximum 15% increase in actual BC will be observed. This is based on just a few instances so it could vary quite a bit over the broad spectrum of nose shapes and bullet weights.

    Hope this helps.
    Respectfully,
    Tom Myers
    Precision Shooting Software


  3. #23
    Boolit Grand Master

    Wayne Smith's Avatar
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    I second the nomination for a stickie.
    Wayne the Shrink

    There is no 'right' that requires me to work for you or you to work for me!

  4. #24
    Boolit Master
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    Do any of these sources list the LOA of the cast bullets?

  5. #25
    Boolit Grand Master Artful's Avatar
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    NOE 311247 FN Whisper/Blackout - BC as calculated by Moonie at .436
    http://castboolits.gunloads.com/show...ghlight=311247

  6. #26
    Boolit Master

    fatelvis's Avatar
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    Excellent info, thanks! Can anyone tell me what the BC is for Lyman's 358627? Thanks-
    I shoot so that I can handload.

  7. #27
    Boolit Master

    Tom Myers's Avatar
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    Quote Originally Posted by fatelvis View Post
    Excellent info, thanks! Can anyone tell me what the BC is for Lyman's 358627? Thanks-
    fatelvis,

    I don't have a Lyman 358627 bullet but I do have a Lyman sketch of one so I scaled it out and entered the dimensions into the Precision Cast Bullet Design and Evaluation software. Enclosed are the results of the calculations and drawings.

    The estimated B.C. calculation is 0.2533.

    Hope this helps.





    Respectfully,
    Tom Myers
    Precision Shooting Software


  8. #28
    Boolit Master

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    Thanks!
    I shoot so that I can handload.

  9. #29
    Boolit Master




    Scharfschuetze's Avatar
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    I also would like to say "thanks" to the guys that typed out those BCs for all the different moulds. As noted, all BCs are approximate, but these numbers are a good place to start.
    Keep your powder dry,

    Scharf

  10. #30
    Boolit Master Marlin Junky's Avatar
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    Has anyone derived a BC for SAECO 301 based on actual chronograph data?

    MJ
    It's not about gun control, it's about people control. The progressives are using terrorists and the insane to further their agenda. If the socialist news media wasn't complicit, we could sit back and watch Fast & Furious and Benghazi-gate unfold.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check