How do you correctly measure groups ?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Down Under Hunter, Jan 1, 2008.

  1. Down Under Hunter

    Down Under Hunter Well-Known Member

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    Just wondering the correct way to measure group sizes. I would imagine it is some calculation with verticle spread, horizontal spread and distance shot at ?

    I just shot the group of my life so far- 1.75 " centre to centre of all 3 shots horizontally and .75" verticle spread centre to centre at 700 Meters. What does this equate too ?

    Don't really know ?

    DUH
     
    Last edited: Jan 1, 2008
  2. britz

    britz Well-Known Member

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    Just measure the width of the two outermost holes, avereage them, measure from the outside point to outside point, and then subtract the average width of the holes (the reason for measureing the actual width of the hole is because paper stretches or tears irradically sometimes- a 30 cal bullet may or may not leave a .308 inch hole). Way to go on your group!
     

  3. Stormrider

    Stormrider Well-Known Member

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    About 1/4 moa. Great shooting!
     
  4. sambo3006

    sambo3006 Well-Known Member

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    Great group!
    For all practical purposes, one minute of angle (1 MOA) equals one inch at 100 yds, two inches at 200 yds and so forth. So what stormrider said basically means you shot the equivalent of a 1/4" group at 100 yds--although what you did would actually be harder due to wind drift and velocity differences from shot to shot at that distance. Your vertical dispersion is a better indicator of load precision at long range than horizontal spread due to wind drift, assuming your barrel is free floated and is not excessively hot during shooting.
     
  5. royinidaho

    royinidaho Writers Guild

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    You said: I just shot the group of my life so far- 1.75 " centre to centre of all 3 shots horizontally and .75" verticle spread centre to centre at 700 Meters. What does this equate too ?

    I reply: Great Shootin'

    Measure with calipers from outside edge to outside edge of the carbon mark of the widest shots. Then subtract at least one caliber and maybe fudge just a little. Then round it of DOWN to the nearest 1/100th. That's the group size that you advertise.;)

    the sad thing is that if that rifle does it once, "IT" will do it all the time.:eek::D:D
     
  6. Down Under Hunter

    Down Under Hunter Well-Known Member

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    Roy,

    Just pleasing to know it has the capability, even if I dont ?

    I'm going to stick a jewell trigger in it, so hopefully thing can only get better as they say !

    Cheers guys !

    DUH
     
  7. goodgrouper

    goodgrouper Well-Known Member

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    The confusion of group measuring may account for why I hear "my gun shoots 1/4" all day long" so many times a week. I think those guys are measuring the paper between the closest two holes!! Either that or every swinging Harry that says that is shooting competitive benchrest aggs every time he goes out and I doubt that very seriously.

    The best way to field measure is to do like Roy said. Measure from outside to outside of the hole and subtract the caliber. But that way is still not accurate enough for benchrest measuring. We actually have a tool that attaches to a caliper and works very well and much more accurate.
     
  8. Down Under Hunter

    Down Under Hunter Well-Known Member

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    GG,

    I guess I just wanted to know just approx where I was at ? I also shot a couple of 2 shot groups that were both inside an inch side by side at 415 M. I'll take that for a hunting rifle.

    Just starting to get a feel for the gun as it is early days, but the signs are encouraging.

    Thanks

    DUH