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Thread: Let's Talk About "Accuracy"

  1. #21
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    Quote Originally Posted by Koshinn View Post
    That last bolded AMR should probably be "extreme spread" instead.
    Quite right, edited, thank you.

    Quote Originally Posted by taekwondopreacher View Post
    Thanks for this thread. I'll be using the quoted portion from now on. I don't know why I never thought of this before, but it probably explains why I'm always tinkering with my scope when I zero.
    It's hard to resist the temptation to spin the knobs when you have a nice group just outside where you want the bullets to be going.
    During zeroing, I will adjust boldly on single shots and once I get pretty close to center (within an inch at 100) make my final adjustment (if needed), and then start shooting 5-round groups. I won't make any adjustment to the zero until I have at least 2, and preferably at least 5 groups from which to determine the point that the centers of the groups are revolving around.

    Glad that this has been useful to some folks here.

    If anyone has any questions or wants clarification on anything, please feel free to post. I will reply as best I can, and add/edit the original post to consolidate everything.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  2. #22
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    Does the term "Average Mean Radius" seem redundant to anyone else?

    The word "mean" is a more precise term for the common-use word "average". Unless "mean" is being used as "not nice", which makes no sense but at least isn't redundant.

    You could drop the word "Average" and "Mean Radius" would be just as descriptive... unless AMR is referring to a group of groups. In that case, it would probably be more descriptive if it was called Mean of Mean Radii. Or I guess... very mean radii.
    Last edited by Koshinn; 07-02-15 at 16:25.
    "I never learned from a man who agreed with me." Robert A. Heinlein

  3. #23
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    Quote Originally Posted by Koshinn View Post
    Does the term "Average Mean Radius" seem redundant to anyone else?

    The word "mean" is a more precise term for the common-use word "average". Unless "mean" is being used as "not nice", which makes no sense but at least isn't redundant.

    You could drop the word "Average" and "Mean Radius" would be just as descriptive... unless AMR is referring to a group of groups. In that case, it would probably be more descriptive if it was called Mean of Mean Radii. Or I guess... very mean radii.
    I agree, just the initialization used by the Army, maybe MR got used somewhere else in someone's definition list and they decided to err on the side of redundancy.
    I stopped expecting them to make sense years ago...

    ETA: looks like MR was taken to refer officially to Maintenance Ratio in an Inter-Service Memo.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  4. #24
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    Quote Originally Posted by Failure2Stop View Post
    I stopped expecting them to make sense years ago...
    That is probably a good philosophy.
    "I never learned from a man who agreed with me." Robert A. Heinlein

  5. #25
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    Jack, Thanks for starting this thread. Lots of good discussions - info here.
    I predict future happiness for Americans, if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.
    Thomas Jefferson

  6. #26
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    So essentially, you are making 20 round groups, composed of 4 x 5 round strings (with each 5 round group being overlayed on top of the last, not re-centered to each group center). I can see how this is the best of both worlds...a statistically significant number of rounds fired, a comfortable number of shots per sting, as well as the ability of letting you see how the precision holds up during the progression of strings.

    I'm all for this. I think it meets my personal preference for 10 round (minimum) groups and expands upon that in a useful way.

    Since you have touched upon the topic of shift, can you give any pointers on minimizing cold bore and hot bore shift?
    Great thread!

    Quote Originally Posted by Failure2Stop View Post
    In my experience, 5-round groups tend to help reduce shooter error.
    This usually isn't a big deal right out of the gate, but when you get into the 200 round area shooter fatigue becomes more of a thing.
    Still, that 5-round group on its own is a data point, but that data needs to be populated with several (at least 4) groups to accurately indicate anything usable.

    This comes around to zeroing.
    After my initial zero, I won't touch the turrets until I have at least 4 groups from which to determine actual group center.
    If the group center isn't consistent with regard to point of aim, I want to check heat, and will generally shoot 4X 5-round groups, with enough time between strings to allow the barrel to cool.
    If the group centers become more consistent, I do a heat work-up, shooting 40 to 50 rounds in 5-round groups with only enough time between groups to ensure good natural point of aim and correct position/NPA.
    If the group to group dispersion does not improve, I at least know that the issue is probably something other than heat.

    When it comes to data collection, I am more interested in group centers in relation to the POA than I am in individual group size. After shooting the gun for a while, I know what the groups should look like, and anything weird (large) gets noted.
    Last edited by P2000; 07-06-15 at 22:53. Reason: Added the following: (with each 5 round group being overlayed on top of the last, not re-centered to each group center)

  7. #27
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    Jack,

    Thanks for the thread... awesome write-up!

    I too, would like to delve further into the Topic of POI Shift, especially concerning Zero's and First Round Hit Probably. I had briefly read about Bryan Litz's WEZ Analysis, but haven't really finished it all yet.

    I'm def. curious as to how an AR15/AR10 system stacks up against Bolt Guns such as AI/Sako TRG/M24/M40 etc. concerning Shift.

  8. #28
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    Edited to add depth regarding the 0.5 MOA gun with 1.5 MOA of shift in the last part of the write-up.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  9. #29
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    Quote Originally Posted by P2000 View Post
    So essentially, you are making 20 round groups, composed of 4 x 5 round strings (with each 5 round group being overlayed on top of the last, not re-centered to each group center). I can see how this is the best of both worlds...a statistically significant number of rounds fired, a comfortable number of shots per sting, as well as the ability of letting you see how the precision holds up during the progression of strings.

    I'm all for this. I think it meets my personal preference for 10 round (minimum) groups and expands upon that in a useful way.
    To nit-pick: I am talking about data based on not less than 20 rounds to track zero.
    The zero is a living organism. It is born/hatched/sprouted only after careful incubation of information.
    Recording data following that "feeds" the zero, keeping it alive and useful.

    Since you have touched upon the topic of shift, can you give any pointers on minimizing cold bore and hot bore shift?
    Once a barrel is broken in, I believe that most* cold bore shift is actually cold shooter shift.
    With regard to minimizing shift at higher round-counts, another variable creeps in: mirage (more precisely: thermal turbulence).
    As the barrel get heated up, it heats the air around the barrel/suppressor, causing it to rise. The difference in density between the hot air and colder ambient air causes the image of the target to shift and shimmer, making precise POA hold more difficult.
    Of course, a hot barrel has different physical characteristics than an ambient temperature barrel, which further introduces variables.
    The traditional approach to reduce this effect is to use a thick barrel, which heats up slower and more uniformly. The downside is that they also cool-off slower that a barrel with less mass. Various approaches, from increasing surface area to direct cooling, have been utilized to get the barrel back to ambient temperature more rapidly. The problem is that they still get hot (or at least significantly hotter). FWIW: most common approaches to increasing surface area to cool faster simply do not have enough area to bleed heat to air. Look at the heat sink on a CPU. Something similar, of larger scale, would need to be on a barrel to add enough surface area to significantly change the cooling attributes of a given barrel.

    As a shooter, it is more important to me to know what the effect is, and when it starts to be a factor. Every gun is unique, and density of fire is an important variable.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  10. #30
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    Quote Originally Posted by HD1911 View Post
    I'm def. curious as to how an AR15/AR10 system stacks up against Bolt Guns such as AI/Sako TRG/M24/M40 etc. concerning Shift.
    As above, a lot of this links to barrel profile and density of fire, which makes it hard to draw a direct comparison.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

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