Correct way to measure a group?

Discussion in 'The Basics, Starting Out' started by skip AI, Oct 17, 2005.

  1. skip AI

    skip AI Well-Known Member

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    What is the correct way to measure a group centre to centre?
    Can someone post a picture example of measuring a group using verniers, would be appreciated.

    Thanks

    Cheers
     

  2. Centre Punch

    Centre Punch Well-Known Member

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    Oct 29, 2004
    Skip,
    From an ex benchrest shooter:
    Identify the edges of your group that are furthest apart and draw a line through the centre of the opposing bullet holes. Set your Vernier on the group so that the edges of the blade form a 90 degree angle with the scribed line at the furthermost edge and take a reading.
    Record this reading and subtract your bullet diameter, this will give you your C-C group.
    If you want to, divide by 1.09 to get MOA.
    Hope the pix will help explain.
    [​IMG]
    My 243 Group.
    [​IMG]
    308 Group

    Ian.

    "I meant to shoot the pike but the duck got in the way"
     

  3. zingdingo

    zingdingo Well-Known Member

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    I am far from an expert on this subject, but I'm sure that I have read that the holes left in paper targets are usually a little bit smaller than the caliber size. If this were true, it would make groups measured using this method prone to being slightly smaller than they actually are. The amount of effect this would have on relative group size (that is percentage) should increase as the group size decreaes. That is, on a 2" group a .1" error would make much less difference than on a .2" group. I've heard of actually measureing the centers of the bullet holes, however, I don't know of any superior way to do this.
     
  4. LOBO

    LOBO Well-Known Member

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    I measure outside to outside on the farthest bullet holes, then subtract the bullet diameter. This will give the same result as measuring center to center.
     
  5. skip AI

    skip AI Well-Known Member

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    Thanks all, now I know how to do it 'properly'

    Cheers
     
  6. moosehunter

    moosehunter Well-Known Member

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    Now that depends also on where you are when the group is discussed. In comp. and at the range we measure the group outside to outside then subtract caliber. Later when talking about group sizes in the bar knocking back some cold ones the usual accepted practise is to automaticly eliminate the flyer, measure the remaining bullets then subtract the largest caliber you have at home. Also dont forget that the distance the group was shot at must be multiplied by 1.5
     
  7. Buffalobob

    Buffalobob Writers Guild

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    One thing that will help your group size is to take your target to work and put it in the copying machine and set the machine for 50% reduction. /ubbthreads/images/graemlins/grin.gif Sometimes, if I am having a bad day I have to use more than 50% reduction /ubbthreads/images/graemlins/blush.gif
     
  8. Eaglet

    Eaglet Well-Known Member

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    Now!!! that's a good sence of humor...LOL.. /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/smile.gif