HK SP5K - First Red Dot - Where To Zero? - Page 2
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Thread: HK SP5K - First Red Dot - Where To Zero?

  1. #11
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    Quote Originally Posted by kaltesherz View Post
    Zeroing at 25 yards should also put you on at 100 yards too, kinda like the 50/200 zero with M4's.
    i don't see this with that ~4.5" barrel

  2. #12
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    Quote Originally Posted by ipsilateral View Post
    Do you have more info on this? I was under impression 9mm had about a 12" drop at 100 yards
    https://www.youtube.com/watch?v=oazgLCWt_II

    Sorry, I guess the extra barrel on the full size MP5 makes the difference.

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    Quote Originally Posted by kaltesherz View Post
    https://www.youtube.com/watch?v=oazgLCWt_II

    Sorry, I guess the extra barrel on the full size MP5 makes the difference.
    Maybe I'm missing something. But, doesn't the height of the optics over the bore-line come into play? For a handgun, the sights may be around .25 to .5 inches over the bore-line. Although small, the sights would be /could be used to take this out, as well as the several inch drop at 25 yards. It does thus by essentially forcing the bore to be slightly tilted up.

    From the video, it looks like the optics are around 3 inches or so above the bore-line. I would think that the sight alignment for a 25 yard zero would also have to take this out as well as the gravity drop. This would force a larger tilt. A half inch tilt at 25 yards would boresight about 2 inches at 100 yards (4 times greater). Correspondingly, a 3 inch tilt would boresight at around 12 inches higher at 100 yards. This could account for the aimpoint performance observed since it would compensate for the gravity drop.

    Am I missing something?

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  5. #14
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    Quote Originally Posted by hgratt View Post
    Maybe I'm missing something. But, doesn't the height of the optics over the bore-line come into play? For a handgun, the sights may be around .25 to .5 inches over the bore-line. Although small, the sights would be /could be used to take this out, as well as the several inch drop at 25 yards. It does thus by essentially forcing the bore to be slightly tilted up.

    From the video, it looks like the optics are around 3 inches or so above the bore-line. I would think that the sight alignment for a 25 yard zero would also have to take this out as well as the gravity drop. This would force a larger tilt. A half inch tilt at 25 yards would boresight about 2 inches at 100 yards (4 times greater). Correspondingly, a 3 inch tilt would boresight at around 12 inches higher at 100 yards. This could account for the aimpoint performance observed since it would compensate for the gravity drop.

    Am I missing something?
    The HOB doesn't matter at all for zeroing purposes. You zero it at a given distance, and that's that.

    Where it does begin to show effect is in the falling branch of the trajectory, where the second line of sight crossing will occur.

    Aside of changing the HOB, the velocity, or the BC of the bullet, this can't be controlled; you just have to be aware of where it is.

  6. #15
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    Quote Originally Posted by fargo007 View Post
    The HOB doesn't matter at all for zeroing purposes. You zero it at a given distance, and that's that.

    Where it does begin to show effect is in the falling branch of the trajectory, where the second line of sight crossing will occur.

    Aside of changing the HOB, the velocity, or the BC of the bullet, this can't be controlled; you just have to be aware of where it is.
    Are we saying the same thing? For any HOB, you can sight in for 25 yards. But, the larger the HOB the more upward "tilt" (elevation angle) of the bore-line and thus the bullet trajectory will be "arced" above the sight-line. This is what gives the second LOS crossing at 100 yards - and also gives a POI above the sight-line between 25 and 100 yards. It seems to me that this may be the dominant factor as opposed to increased velocity due to longer barrel length.

  7. #16
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    Your sighting system, from irons on the barrel to a powered optic with a giant bell in a high mount, is over the bore. There will always be a height over bore. The sight line is straight whereas the bullet arc is parabolic. So, the bullet is going to cross the sight line twice (a point at which they intersect, or a zero point) once where you have intended and again somewhere else. Where that other point is will be influenced by the distance between the bore axis and the sight line (the height over bore).
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    Quote Originally Posted by hgratt View Post
    Are we saying the same thing? For any HOB, you can sight in for 25 yards. But, the larger the HOB the more upward "tilt" (elevation angle) of the bore-line and thus the bullet trajectory will be "arced" above the sight-line. This is what gives the second LOS crossing at 100 yards - and also gives a POI above the sight-line between 25 and 100 yards. It seems to me that this may be the dominant factor as opposed to increased velocity due to longer barrel length.
    Yes, I agree. Except that with an MP5, the sights zeroed at 25Y will impact the same elevation at 75Y, not 100. My main point is that there's no changing it. You just have to understand what you've done and where you're going to hit at every distance.
    Last edited by fargo007; 09-13-2017 at 07:55 PM.

  9. #18
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    I would zero at 25M for that weapon. Great for close in and flat shooting for up to 100M.
    So many HKs so little time.

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