Actual vs PC based drop/drift etc.

Discussion in 'General Discussion' started by POP, Oct 17, 2006.

  1. POP

    POP Well-Known Member

    Jul 25, 2001
    Question for anyone who is willing to answer. How do you go about creating an accurate MOA chart for drop/drift if one is limited to let's say a 200 to 300 yard range? How much diff is there between actual and PC drop figures and is there a way to make them more applicable to your gun/load based on figures ascertained from 200 or 300 yard drops?
  2. sniper2

    sniper2 Well-Known Member

    Jan 10, 2003
    Your last question will answer the first. I have several programs for ballistics and while they are close I still shoot and document results in different conditions.It doesn't matter what the best programs say if you shoot and document your own results first hand experience and practice are unbeatable.Try to find the heavier bullets with the best BC s for your given rifle and wind shouldn't be too much of a problem at the distance you are concerned about, always practice at the distances and conditions that you will be hunting then you will have less suprises...

  3. CatShooter

    CatShooter Well-Known Member

    May 8, 2001
    [ QUOTE ]
    ... How much diff is there between actual and PC drop figures and is there a way to make them more applicable to your gun/load based on figures ascertained from 200 or 300 yard drops?

    [/ QUOTE ]

    There is some difference.

    Some years back, I was loading up some Sierra BlitzKings for a bench grade long range crow/PD rifle.

    Sierra's "Infinity" software is some what primitive, so they have to test each bullet and assign different BC's at different velocities to make up for errors. So it SHOULD be good - right?

    So (one would think) is should be accurate for their own bullets.

    I got my most accurate loads, got repeatable velocity readings (two chronographs).

    And then I made a drop chart for long range "predictions".

    When I tested the loads for drop at 100, 200, 300, 400, by the time I was at 300 yds, I needed to make changes in my chart, and 400yds was off by 1.75" (low).

    Needless to say, for a rifle that is to be used for small targets out to 600/700 yds, that's piss poor predictions.

    (And yes, I did do the temperature, altitude stuff).

    I think the Sierra software is not capable of building a long range shooting chart if your targets are small.

    Sierra got into this crappy software about 15 years ago (remember DOS 3.1 /ubbthreads/images/graemlins/wink.gif ), and now has so much money and time invested in it that they can't get out.

    I bought some new software recently that I used for my 50BMG, and it is amazingle good, predicting long range hits with M-48's.

    But I have not had the time to critically test it with a bench rest grade rifle.

    One thing to remember when using these programs is that the altitude and barometric pressure are not as they seem.

    These entrys are interlocked. All these programs use the aviation sea level standard for barometric pressure, and then calculate elevation and change barometric pressure.

    So... if you are in Denver (at 6000 feet amsl), and you hear the barometric pressure on the radio as 31 inches. You enter 6000 feet and 31 inches into the program, and go.

    The local barometric pressure (which would be 25") from the weather station has been converted to sea level (by the weather dept), and your program is converting it back - which is exactly what it is supposed to do.

    BUT - if you enter the local "real" barometric pressure from one of the hand held weather devices like a Kestral 4000, you will get shooting solutions for 12,000 altitude, because the software is assuming that the baro is from sea level.

    So... if you use true local pressure from a hand held guage, you MUST enter "0" as altitude.

    Also keep in mind - BC's from different companies are not the same - Bullets with a BC of .370 from Sierra, Hornady and Nosler will not fly the same, because there is no standard protocol for determing BC, and each company uses different software, and different methods to determine "their" BC.

    It has been my experence that Sierra BC's are inflated, and a Hornady bullet with a .300 BC will fly flatter than a Sierra Bullet with a .300 BC.

    I know... it's boring!