Measuring a group size

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by DEATHGRIP, May 11, 2015.


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  1. DEATHGRIP

    DEATHGRIP Active Member

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    What is the "official" way to measure a group size? Is it outside measurement or is it center to center of the outside holes? I have seen what some call a half inch and it looks way bigger than what i consider a half inch group. Enlighten me please.
    Dave
     
  2. bigngreen

    bigngreen Well-Known Member

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    Measure largest outside to outside and subtract bullet diameter.
     
  3. FearNoWind

    FearNoWind Well-Known Member

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  4. MMERSS

    MMERSS Well-Known Member

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    "Officially" count all the shots. In golf it's called a Mulligan. In shooting they are called flyers. It's amazing at times how many Mulligans a person will not count during a round of golf.
     
  5. dragman

    dragman Well-Known Member

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    Winner. gun)
     
  6. DEATHGRIP

    DEATHGRIP Active Member

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    Thanks Guys.
     
  7. davkrat

    davkrat Well-Known Member

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  8. Mikecr

    Mikecr Well-Known Member

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    Subtract an actual hole diameter(from a fouler on the same paper/backer/distance, rather than bullet diameter. There is often a big difference.
     
  9. sp6x6

    sp6x6 Well-Known Member

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    I shot comp small bore and you use a gauge that has a magnify ring on it above the actual caliber shot,placed in hole then looked at by judges to see if it hit score ring.Very obvious most times used on close calls.That dictated where bullet edge was
     
  10. LouBoyd

    LouBoyd Well-Known Member

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    What do "official" and "group size" have to do with hunting? The measurement techniques described above are right for bench rest and similar competition, but shooting for score on target rings is somewhat more realistic as the measure of a hunting rifle. No form of fixed range repetitive shooting competition gives a good indication of how effective the shooter/rifle/cartridge will be in actual hunting conditions. I don't know of any formal form of hunting competition (NRA silhouette?) where group size is used in scoring.

    That's not to say a hunter shouldn't test and know the the expected shot to shot distribution of his rifle/cartridge vs distance by testing, but there's nothing "official" about that. Extreme spread (ES aka group size) and standard deviation (SD) are generally considered the important measurements, though knowing the pattern intuitively is at least as important as the two numbers.
     
  11. Wachsmann

    Wachsmann Well-Known Member

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    So if your gun shoots 1/2 MOA at 100yrds lets say 0.5 then and its a 30 cal. So U have .5-.308= .192. So do you have a .192MOA at 100 or do you have a gun shooting 0.5 at 100yrds. This makes a hell of a difference when buying a gun. Because if some one told me there gun shot .192 at 100yrds and you were buying it and it was really shooting .5 at 100yrds. Seem to be a big difference in what your expecting. If thats the case does the accuracy quotes follow this type of logic when companies place a shooting quote on there guns for accuracy.
     
  12. davkrat

    davkrat Well-Known Member

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    No if you measure from outside edge to outside edge you over measure by the diameter of the bullet hole so you subtract one caliber. If you measure inside edge to inside edge I suppose you would add a caliber. Or even easier just measure from outside of one bullet hole to the inside of the furthest.

    The On Target software is the best though. It will tell you any of the ridiculous measurements you want. I don't believe most of the claims I read on the internet anyways. I have shot bughole groups with every gun I've owned and could easily throw up one or two targets and brag about them but the truth is my gun shoot around 1 MOA when I get a load dialed in. At least they always did with cup and core, lead free is proving to be a challenge.
     
  13. Mikecr

    Mikecr Well-Known Member

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    Lou's right, and this where many hunters and competitors(both) misunderstand differences in accuracy, field accuracy, and precision.
    When you consider the measured performance attributes of a given gun, you have to take into account the comparison standards -for that gun's use. In other words, focus on what matters.

    For LRH, grouping means nothing. What matters in LRH is field accuracy-vs-killzone, as this sets your limits(which you should always stay within).
    Now this is not simple. It takes a good amount of honest/objective testing to determine. It can take huge efforts to improve on. You might find that a bad grouping gun is actually the most accurate gun you've ever shot! And then it's as possible that gun would let you down in field accuracy.. You can't predict it, and you never know until proven.
    It's important that you don't fixate(or compete with your buddies) on the wrong attribute.

    -Accuracy is center of impact(POI) to center of mark(POA). It's definable with any or all single shots.
    You could say furthest POI of .524" from POA = 1/2moa accurate.
    -Field accuracy brings in accuracy per field situation.
    With this you qualify accuracy with range, rest, air density or bore conditions,etc.
    You could say a POI of 3.14" cold bore, off a bipod, at 600yds = 1/2moa field accurate.
    -Precision is grouping, and is independent of accuracy.
    -Precision and accuracy combined for 'probabilities' is called Trueness(useless to competitors and hunters).
     

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  14. FEENIX

    FEENIX Well-Known Member LRH Team Member

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    I like the KISS method too ....... :D



    and

     
    Last edited by a moderator: Sep 8, 2018