Measuring group size?

Discussion in 'Technical Questions & Information' started by Gene Seward, Apr 1, 2009.

  1. Gene Seward

    Gene Seward Member

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    I have always seen group size of a five shot group, but lately have seen so many three shot groups listed in magizines. First which is correct, and how do you measure those groups? Is the reason for three shot groups because they are so much smaller that it makes the manu. products look better? Thanks.
     
  2. artabr

    artabr New Member

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    There is less chance for error with 3 shots verses 5 shots. I prefer 5 shots.
    Best way to get an accurate measurement is to measure the two furthest edges of the group and then subtract the bullet diameter. You can measure to the center of the furthest bullet holes, but I find the first method more accurate.
    Plus what do you do if your group is one hole and you can't find the center.



    Art
     
    Last edited: Apr 1, 2009

  3. CampingJosh

    CampingJosh Well-Known Member

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    If it's just one hole? You quit worrying about measuring it! ;):D
     
  4. 308 at my gate

    308 at my gate New Member

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    I have always measured for 5 shot groups. It is harder to get MOA with 5 shots then 3.
     
  5. gdmoody

    gdmoody Moderator Supporting Member

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    Ain't that the truth!!:D:D
     
  6. LDBennett

    LDBennett Well-Known Member

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    The magazines use two standards: hunting guns, and target or varmint guns. The later uses the five shot groups while the former uses three shot groups.

    The hunting gun argument is that you can only carry three rounds in the gun for hunting in most states so why not measure accuracy in a way representative of real life usage.

    Target of varmint guns shoot long strings so a better representation of their accuracy potential is necesary. The more shots in the test target group the better you can assess the accuracy potential. Five shot groups is just about the minimum group size for any resonable measure of potential accuracy, statistically.

    But regardless of 3 or 5 shot groups you can not get a real reading of the potential accuracy from only one group. You must shoot at least 5 groups, then average the results to get a statiscally relevant meausre of potential accuracy.

    To further muddy the waters, the NRA publication often publishes results from ten shot groups! But when comparing your own guns you can use any system that works for you. To compare to others guns then you should stick to the established unoffical guide of 3 shot groups for hunting guns and 5 shot groups for target and varmint guns, both averaged over at least 5 groups. Always reveal your process to others so that you are not comparing apples to oranges. That is the only way that group size bragging makes sense to me.

    LDBennett
     
  7. Gene Seward

    Gene Seward Member

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    Sounds like a winner to me. That is exactly what I wanted to know. I love this site more everyday. Good shooting to all.
     
  8. USMC-03

    USMC-03 New Member

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    I think that LD has pretty much hit the nail on the head. I often use 10 shot groups for evaluating new loads out of my match rifles, but then we usually shoot 20 shot strings for score too. When I'm trying to track the historical data I will also use one target over for every shot string but stapled behind the fresh target. That way I will have maybe five targets with 5 or 10 shots each for group and then also one target with a group of all rounds shot.
     
  9. gdmoody

    gdmoody Moderator Supporting Member

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    The Army uses a three shot group to zero the iron sights on the M-16's. At least they did before I retired in 96!