Bullet Drift

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by BRrooster, Aug 24, 2014.

  1. BRrooster

    BRrooster Member

    Messages:
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    Feb 7, 2009
    I was out burning some powder yesterday , and was having some trouble hitting the paper at 500 yards. My targets are home made out of a standard 8 1/2 by 11 inch
    sheet of paper. I made a 4 inch diamond template cut out and spray paint it
    orange on the center of the paper, it works great . You can see it clearly, with my Bushnell Legend 5x15 Mil dot scope. One dot lets you see a little of the orange around
    it. I am shooting a rebarrelled Sako in 7MM Dakota. 160g bullets at a little over 3200fps. 1.5 Mils is about right.
    Any way, the place I found to shoot at 500 yards is a slight left to right downhill shot.
    I'd guess about 5 to 10 degrees. Would that cause any drift problems? There was very little wind , maybe 3 to 5mph. I held off 3 inches to the left. My bullet impact grouping was 8 inches to the right of center. I shot prone, using a bipod.
    Just curious if sidehill shooting does anything different to bullet drift.
    cheers
    bruce
     
  2. Screwey1

    Screwey1 Well-Known Member

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    Dec 13, 2013
    What bullet? Wind read with wind guage? How was shot placement vertically?
    My 7mm rem mag shooting a 168 gr berger vld ( high BC bullet ) in a 5 mph wind at 500 yards will push 7 inches. A 7 mph wind pushes 9 inches.
     

  3. BRrooster

    BRrooster Member

    Messages:
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    Feb 7, 2009
    160g sierra sbt, yes I used a wind meter, and had plastic tape wind indicators at two places between me and the target. Im not a super shot , my grouping was ok vertically and about 8 inches round. I hit the target twice out of 8 shots.

    I just read another thread that someone did, asking about "spin drift". I dont think that is my issue, but the replies also mentioned doing a line test with my scope. I havent done that yet, as I havent done a lot of long range shooting, but will do that my next trip out.
    cheers
     
    Last edited: Aug 24, 2014
  4. FearNoWind

    FearNoWind Well-Known Member

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    Jul 10, 2012
    You're correct. Spin drift is not your issue at 500 yards. My best guess would be wind. It's very easy to see 3 MOA of drift at that distance in the load you describe. Best I can figure for that bullet is wind drift at about 5 inches and if you factor in any other possibility of influence it's pretty easy to pull a shot off target when the target is only 8.5 inches wide (you've only gotta be 4.25 inches off)
    The Bushnell Legend 5x15 Mil dot scope may also be a contributing factor. It's pretty light for the rifle you're shooting.
    I don't know what it's mildot spacing is and at what power the spacing is based on but it doesn't take much of an error in mildot calculations (with in the manufacture or field use) to create a substantial error at 500 yards.