Tell me alittle about S/D

Discussion in 'Reloading' started by summitsitter, Aug 5, 2008.

  1. summitsitter

    summitsitter Well-Known Member

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    Could someone please explain in D.A. terms and what effect sectional density has on accuratcy
     
  2. Cruizin

    Cruizin Well-Known Member

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    I don't feel sectional density has much to do with accuracy. It affects penetration more than anything. When looking for a bullet for hunting you will want to compare this number with other bullets of the same weight. If you find one bullet to have a higher sectional density than another it means it will penetrate better than the other.

    Now on the other hand standard deviation (SD) has quite a bit to do with accuracy.
     

  3. boomtube

    boomtube Well-Known Member

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    Actually, Sectional Density (SD) has no influence on accuracy at all. Nor, with modern bullets, does it have any meaning for predicting penetration.

    Consider this; ALL bullets of a given diameter and weight have the same SD. It makes no differnce if it's a hollow point, spire point, round nose, thin jacket, full metal jacket, fused core, a solid or partition, if they are the same diameter and weigh the same they have the same SD. No way will they give equal penetration.

    Back in the dark ages of bullet making, say 50 years ago, bullets tended to be simple "cup and core" with a few distinct exceptions like Nosler and Barnes bullets. Nothing bonded the jacket to the cores so light bullets at high velocities tended to rupture and often failed to penetrate far. The only way to get greater penetration was to use a heavy (for caliber) bullet, which insured a lower terminal velocity and greater mass to help it carry through.

    Modern bullet makers have changed all that. A light Barnes (and others) with a low SD will out penatrate a heavy for caliber soft point bullet with a thin jacket even tho it has a higher SD.
     
  4. edge

    edge Well-Known Member

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    IMO, a high SD bullet will need more twist than a low SD bullet per caliber. All things being equal, you will launch a lower SD bullet faster which is generally less stable than an optimum bullet and a high SD bullet may never fully stabilize.

    Assuming you choose you bullet and twist properly then SD probably does not effect accuracy.

    edge.