POI dramatically changes with scope magnification changes

Discussion in 'Long Range Scopes and Other Optics' started by cdre, Apr 3, 2013.

  1. cdre

    cdre Member

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    Mounted my Simmons Truplex 3x9 scope on my Glenfield 60 and finally took it to the range today. Sighting in, it consistently shot low and at 9X magnification I ran out of adjustment about 3" low at 25 yds. Figured out if I zoomed out, I could get the POI to come back up. Ended up zeroing it in at 5X magnification.

    Pics below show the difference in POI based on magnification changes. Anybody have any ideas as to why this is happening and what I can do to remedy the situation? Is the scope bad?
     

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  2. cdre

    cdre Member

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    A pic of the rifle.
     

    Attached Files:


  3. cdre

    cdre Member

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  4. westcliffe01

    westcliffe01 Well-Known Member

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    Is it brand new ? If so I would return it immediately. When you rotate the zoom ring you are moving an optical group forward and backwards and that group is not moving coaxially to the scope centerline.

    Having said that, how the heck did you run out of adjustment zeroing the scope at 25 yards ? Something is way off with the rings/bases. It should not take much more than a few minutes on the elevation and windage to dial a scope in.

    Re-zero the turrets to the center of their movement and bore sight the rifle then figure out what is going on with the rings. Shooting low means you are aiming high. Is it possible the front and rear base are reversed ? Of that the front and back ring are different ? Sure those are the right bases for your gun ?

    Mmm according to this http://www.castbullet.com/misc/m60.htm it does not look like bore sighting is possible. Is there an integral 11mm dovetail in the top of the receiver ? The rings bolt right to that ? If that is the case and they are the right rings, it suggests that the barrel/receiver are crooked and the scope is pointing up in the air.
     
  5. cdre

    cdre Member

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    The scope is brand new. You are right, I should probably send it back.

    From everything I've read, the scope and included rings are correct for the rifle. Nothing indicates the rings are different front/rear. The clamp directly to the dovetails in the receiver.
     
  6. westcliffe01

    westcliffe01 Well-Known Member

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    You do need to check the barrel to receiver alignment. If the integral rail is in good shape and you are positive that the rings are properly seated and matched, then either the scope is totally defective (seems likely) or the barrel/receiver joint is out of whack. If you took the barreled action out the stock and took it to either a machinist or a gunsmith, then could set up the barrel in V blocks, get it leveled and then indicate the receiver to see if it is straight/level.

    If it is not, then how to correct it gets highly complicated... Perhaps involving a press brake, like they apparently use at Savage to get the barrel aligned with the receiver...

    So send the scope back and when you get a replacement, see if that solved any issues (don't crank the heck out of the turrets though, leave them zeroed and bring the target closer until you actually make it on the paper.) That will give you a good idea how out of whack anything is (if you measure the distance to the target exactly, it can be used to calculate angles). Don't be afraid to shoot at 10 yards if thats what it takes.

    If you are only out vertically, it may be possible to place a shim on the top of the dovetail to raise the rear ring, which will raise the point of impact. Perhaps also a shim under the scope tube in the back ring to raise it even more. Its only a 22, so there is no need to torque the heck out of the rings anyway and I am assuming it hardly has any recoil.
     
  7. bruce_ventura

    bruce_ventura Well-Known Member

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    Westcliffe01 is on the right track, but I recommend not doing anything to diagnose your rifle using this particular scope. The scope obviously has a de-centered lens in the erector. The rifle may actually be ok.

    When you get the replacement scope, I recommend finding the optical center using the mirror method. Optically centering the crosshair, will allow you to use scope to check boresight alignment between the rifle bore and scope tube axis. The mechanical center is often not the same as the optical center on low cost scopes. That's because the crosshair sometimes stops moving before the turret reaches the end of its travel.
     
  8. COBrad

    COBrad Well-Known Member

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    Send it back, get it fixed, then get rid of it. Those cheap Simmons scopes are crap to begin with.
    That Glenfield rifle is cool though.
     
  9. Greyfox

    Greyfox Well-Known Member

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    I'm in agreement with many of the previous comments. The only other thing I would add is to make sure that you are not experiencing parallax effects which can be extreme at close ranges with some scopes and falsely give the impression that your scope is faulty.
     
  10. cdre

    cdre Member

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    Already started the return process... hopefully the next one is better. Don't want to dump too much money in high end optics on it since I mainly want to use it to stay proficient when out of hunting season...
     
  11. joseph

    joseph Well-Known Member

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    I have the same scope on my 10-22 and finally left at one power and use it for squirrels.

    gt40
     
  12. westcliffe01

    westcliffe01 Well-Known Member

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