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Thread: POI and zoom

  1. #1
    Inactive Member

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    Default POI and zoom

    Hi all.

    Does the point of impact change depending on the magnification level that you have zeroed the rifle, ie I zeroed on 25 m with magnification on 10X if I were to go to magnification of 6X on 25m will the POI still be the same? %-6

    Might be a silly question but just had to ask.

  2. #2
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    In theory it should stay the same, my best advice would be to test this.
    With good quality scopes it should stay the same, where it does change is with mildot spacings, they change as the magnification is changed.

  3. #3
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    OK. Does this mean if I was to aim off 2 milldots at 25m (going for the same mark or bulls eye) and shoot at 6X and then at 10X the POI would have changed?

  4. #4
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    Yes it would change.
    As the magnification changes so does the distance between the mildots.
    That is exactly why I like to dial in for a specific distance, center of the reticle will always be center.

  5. #5
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    Read through this JCG, from Leupold

    First Versus Second Focal Plane:

    In variable-magnification optics, the magnification setting for the use of the mil dot reticle is determined by whether the reticle is in the first or second focal plane. The easiest way to determine if the mil dot reticle is in the first focal plane is to view the reticle through the scope while changing the magnification setting. If the size of the reticle appears to change as the magnification setting is changed, the reticle is in the first focal plane. If it does not appear to change size, it is in the second focal plane.
    If the reticle is in the first focal plane, no specific magnification setting is required to obtain the proper subtension to yield accurate range estimating results.


    hth

    ...

  6. #6
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    Hey JCG

    Here's a nice doc on the mil dot system... Sometimes a bit to technical - but nice bedtime reading.

    http://www.snipersparadise.com/training/mildot3.htm

    ...

  7. #7
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    more sily question from me:

    what is zeroed scope?

  8. #8
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    When you 'zero' a scope, you align cross hairs to the point of impact (POI) that the pellet makes on the target.

    People will say something like, I'm zeroed at 35 meters.

    This would mean that when shooting at a target 35 meters away you place the cross hairs exactly where you want the pellet to impact.

    Thus for distances other than 35 meters, you would aim above or below the desired target by a certain amount. (Or change the scopes elevation setting which in effect is changing the zero - known as 'dialing'.)


    ...

  9. #9
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    i see, i zeroed scope at 30m today with 10x zooming. perfect.

    but the pellet go down 5cms when i set 4x zooming and try to shoot a 5m target.


  10. #10
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    At 5m, your pellet is still rising, kinda hard to explain without a diagram of sorts.

    Download the program called "Chairgun" boondock.

    You can get it off of Lewis's site.
    https://www.airrifle.co.za

    In the downloads > software section.

    Once installed you enter you rifles details, power / zero distance / pellet - and it will plot a graph for you. Actually many graphs to play with.

    Very informative on pellet trajectory and POI.. etc...

    hth

    ...

  11. #11
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    at 5m. with 4x zoom. the pellet droped 5cms.

    i got sw . thx avion

  12. #12
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    When looking at the trajectory of ANY projectile it starts losing speed the minute it leaves the barrel (except for rockets and the like).
    People make the mistake of thinking that the pellet rises before it falls, it actually doesn't, what you basically do with a scope is you align the crosshair with the pellet arc. Your scope is not really mounted straight.
    A airgun shooting a 8gr pellet at 800fps with a zero on 25m will hit low up to about 20m, then be on target (or very close) to about 30m and then start to hit low again. How low it will hit at say 10m really depends on how high your scope is mounted above the barrel. To keep it simple use the lowest mounts that you possibly can.
    Go read up on this on the internet (google), you will very quickly learn alot about this, also check around on www.aftsa.co.za

  13. #13
    Marksman
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    I disagree wholeheartedly with the low mounts theory.
    Higher mounts give you a much more useable trajectory, unless you are shooting mostly between 5 and 10m

  14. #14
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    Look at a trajectory. First the pellets inclines, then peaks at an arc, then drops. You can get as scientific as you want, but unfortunately gravity is a fact.

    When you throw a tennis ball for your dog, you throw it upwards at an angle to reach the other end of your garden. Throwing it level it wont get very far. Unless you have a really small garden.


    Agree with guido on the mounts though. Will get a flatter trajectory at longer distances.

    ...

  15. #15
    Marksman
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    not really flatter, trajectory will never change...

    It just puts the line of sight higher relative to the bore so the trajectory crosses over at say 20yds...rises slightly by maybe 2cm at 35 and crosses again at 50, thus giving you a very useable range between 15 and 55yds . You do not really need to compensate in hunting conditions using such a setup...except obviously for very very close shots and beyond 55yds...not shots you take often anyway.

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