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Thread: Sighting a rifle scope at 25 yards for 100 yards

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    Sighting a rifle scope at 25 yards for 100 yards

    I have a an m4 style AR15 with a 16" barrel and I'm trying to sight it in. The biggest range around where I live is only 25 yards. To achieve a 100 yards zero, how high should the POI be from the POA?

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    With a 100y Z your point of impact will be about 1.5" low @ 25y.
    Adjust your sight so that you are hitting 1.5" below your POA.


    About like this:


    * This is a 50y Zero shot at 25. My AR now sports a 100yZ but I don't have a POA/POI pic for that.
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    Last edited by AMMOTECH; 01-17-12 at 15:15.
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    1.5" low, if you search around on here I know there are printable targets for doing just this

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    http://www.m4carbine.net/showthread.php?p=1176195
    These are the ones I used. Just click on the one you need and print it out.

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    Quote Originally Posted by AMMOTECH View Post
    With a 100y Z your point of impact will be about 1.5" low @ 25y.
    Adjust your sight so that you are hitting 1.5" below your POA.
    I'm thinking out loud here. Obviously when you zero your optic at 25 for 100 you need to actually verify your 100 yard zero. Okay, given.

    If you "tweak" this just right, is there a possibility that your 25 for 100 zero means that at 25 you put your red dot on the target, so that at 100 yards you would aim the red dot just under the target?

    This kind of stuff makes my head hurt, but it occurred to me in the real world how handy that would be.
    W.I. Thomas: "If men define situations as real, they are real in their consequences".

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    Quote Originally Posted by Doc Glockster View Post
    I'm thinking out loud here. Obviously when you zero your optic at 25 for 100 you need to actually verify your 100 yard zero. Okay, given.

    If you "tweak" this just right, is there a possibility that your 25 for 100 zero means that at 25 you put your red dot on the target, so that at 100 yards you would aim the red dot just under the target?

    This kind of stuff makes my head hurt, but it occurred to me in the real world how handy that would be.
    Yes always verify at distance.

    @100y with 100y zero you just hold on the center of the target. As the target distance becomes shorter you hold(aim) higher.
    In my pic above I was aiming at the red dot. If I had wanted to hit the red dot I would have had to held over or aimed higher.

    Did this help? Did I get it right....

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    Last edited by AMMOTECH; 01-17-12 at 16:43.
    -David


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    At 25 yards your point of impact should be approximately 1.5 inches below your point of aim. The point of aim needs to be consistent so that your adjustments are based off of a real hold, not an approximation.
    At 100 you will be establishing POA/POI convergence, as in: the bullets will hit where your sighting system is pointing. This is a 100 meter/yard zero.

    "Zero" does not have to mean POA/POI, but it is usually applied that way.
    Jack Leuba
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    Does this work bass ackwards?

    If you want your weapon to be dead on at 25 yards on the theory that you'll face the most opponents at that range or less, yet still want the capability to know where your rounds are hitting at 100 yards, could you assume that your rounds will be 1.5" high at 100 yards?

    In other words, let's say you want to put your dot right on the center of a head shot at 25 yards, but would still like to engage at 100. If your dot is right on the nose at 25, would you assume that you need to hold your dot on the chin at 100?

    Or do I have this all wrong? (Sorry I'm having trouble wrapping my mind around this).

    EDITED TO ADD: I looked back at some of the trajectory charts and it does not seem to work that way for a 25 yard zero, at least not without some other additional holdover or something. The IBZ chart for a 50 yard zero seems to indicate that you can do this.
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    Last edited by Doc Glockster; 01-17-12 at 17:14.
    W.I. Thomas: "If men define situations as real, they are real in their consequences".

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    All the good info all in one place.....
    http://www.m4carbine.net/showthread.php?t=65679


    .
    Last edited by AMMOTECH; 01-17-12 at 17:20.
    -David


    USAF 1987-2008 {461/2W0 Munitions Tech}
    FN Mfg. 2008-???? http://www.fnmfg.com/

    AR-15 owner/shooter since 1998

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    Quote Originally Posted by AMMOTECH View Post
    All the good info all in one place.....
    http://www.m4carbine.net/showthread.php?t=65679


    .
    Yes, thanks. Found the one I was looking for. Looks like it might work at a 50 yard zero but not a 25 yard zero. This chart shows what I was talking about but I'm still not sure I'm looking at this correctly.

    With a zero of 50 yards, do you plan to aim about 1.5" low at 100 yards to hit the same spot you would have at 50?

    (Sorry, not trying to hijack. Just kinda confused).
    Attached Images Attached Images
    Last edited by Doc Glockster; 01-17-12 at 17:35.
    W.I. Thomas: "If men define situations as real, they are real in their consequences".

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    Quote Originally Posted by Doc Glockster View Post
    Does this work bass ackwards?

    If you want your weapon to be dead on at 25 yards on the theory that you'll face the most opponents at that range or less, yet still want the capability to know where your rounds are hitting at 100 yards, could you assume that your rounds will be 1.5" high at 100 yards?

    In other words, let's say you want to put your dot right on the center of a head shot at 25 yards, but would still like to engage at 100. If your dot is right on the nose at 25, would you assume that you need to hold your dot on the chin at 100?

    Or do I have this all wrong? (Sorry I'm having trouble wrapping my mind around this).

    EDITED TO ADD: I looked back at some of the trajectory charts and it does not seem to work that way for a 25 yard zero, at least not without some other additional holdover or something. The IBZ chart for a 50 yard zero seems to indicate that you can do this.
    No you want your zero to cover a wide range of distances you could find yourself in without having to remember to hold over or under. The 50 200 yard zero is about the best as it puts your bullet with in 2.5 inches of your pont of aim from 0 to 250 yards. With a 25 yard zero you will be 4 to 6 inches high at 100 yards if you needed to make a head shot you would miss. This is what causes most new shooters to do poorly at three gun in their first few matches with the rifle. They simply don't know where their rifle hits because they don't understand trajectory.
    pat
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    I have an Eotech but that is not what I am trying to sight in. I am trying to sight in a variable zoom scope. The range is only 25 yards. I want to zero my scope as closely to 100 yards as possible. I had heard from somewhere that to get a 100 yard zero at 25 yards your point of aim should be about 1.5" above your point of impact. Is this true?

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    Quote Originally Posted by Army44 View Post
    I have an Eotech but that is not what I am trying to sight in. I am trying to sight in a variable zoom scope. The range is only 25 yards. I want to zero my scope as closely to 100 yards as possible. I had heard from somewhere that to get a 100 yard zero at 25 yards your point of aim should be about 1.5" above your point of impact. Is this true?
    Yes thats try set your optic up t hit approximately 1.5 inches below your point of aim.
    Pat
    Serving as a LEO since 1999.
    USPSA# A56876 B Class
    Firearms Instructor
    Armorer for AR15 and Glocks.
    YouTube Channel http://www.youtube.com/user/Alaskapopo

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    how close to do you have to be before the optic over bore issue starts?

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    Quote Originally Posted by xjustintimex View Post
    how close to do you have to be before the optic over bore issue starts?
    It is a constant concern for precision placement and varys in severity depending on zeroing method.

    Most crucial at 3 to 15 meters, which is one reason that I have a high preference for a 100 meter zero, as it "flattens" the close range trajectory and alleviates the need to remember different hold-overs, giving broader "chunks" of hold over distance as opposed to other zeroing methods.
    Jack Leuba
    Military/Government Product Liaison
    Knight's Armament Company
    jleuba@knightarmco.com

    Director of Training

    Jack@F2SConsulting.com
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    As accurate as needed, as fast as possible, as many times as it takes.

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