sd and es

Discussion in 'Reloading' started by plumcrazy, Aug 7, 2010.

  1. plumcrazy

    plumcrazy Member

    Jul 6, 2010
    Can someone explain what SD and ES means I hear that alot involving reloading
  2. boomtube

    boomtube Well-Known Member

    Oct 8, 2007
    ES = Extreme Spread.

    For us, it simply means the difference beteen the fastest and slowest velocity of a tested string.

    SD = Standard Deviation.

    It's a statistical/mathmatical thing. Sorta equvilent to "averaqe" BUT not quite the same. More like an average difference of each bullet's speed when measured from the average speed of the tested string. (You get that? Not sure I do!) It's somewhat complex to calculate and very difficult to describe in a few words so just consider it a better way of measuring the quality of our load's vvelocity consistancy.

    Neither factor is of much use in determining a loads accuracy potential at short ranges (inside 300 yd.s). It only affects longer range accuracy when small differences in velocity begin to show up as vertical stringing in the trajectory.
    Last edited: Aug 7, 2010