losing elevation when dialing

Discussion in 'Long Range Hunting & Shooting' started by Codyg510, Sep 10, 2012.

  1. Codyg510

    Codyg510 Member

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    Recently, when shooting at 500 yards with my Millett TRS-1 4-16X atop my rem 700 .308, I noticed the rounds impacting 2.5 MOA low on a recent shoot. I’ve shot at this distance and greater several times and my data from JBM has always been dead on as far as elevation is concerned. I dialed back to my 100 yard zero and shot several rounds at 100 yards to check for a tracking issue. No issues here. The scope returned to zero almost perfectly. How did I lose 2.5 MOA in adjustment at 500 yards in just a couple weeks? Same Ammo, nearly identical weather conditions. I’m not familiar with the internal workings of the scope or how the elevation turret works. I’m hearing definitive click when I rotate the turret although it has always been a little mushy. Any ideas?
     
  2. Joe King

    Joe King Well-Known Member

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    which model number do you have?

    I notice something similar with my Millet scope. Mine is supposed to have 1/8min clicks but it seems more like its 1/10 min clicks. 100yrd zero equals 3moa drop at 300yrds, I have to dial up 4moa for it to be on, but using the reticle to hold the 2.5moa it subtends and my rounds hit exactly .5moa low
     

  3. Codyg510

    Codyg510 Member

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    Not sure about the model number, but it does use 1/4 MOA adjustments. I'm confused because this hasn't been a consistent problem. The 1/4 MOA adjustments were right on up until just a couple weeks ago. Now i'm hitting 2.5 MOA low at 500? I'm wondering if something is slipping inside the elevation turret. I'm thinking of returning to Millett for repair if i can't diagnose the issue.
     
  4. JeffP40

    JeffP40 Well-Known Member

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    First off, don't just assume it is the scope. There are a lot of other variables to consider. Atmospheric conditions can make a huge difference in poi. Take it out and shoot it some more. Put some of your ammo on ice in a cooler and keep some pretty warm. Compare the drops of the two. A lot of the difference may come from temp. Humidity can also affect poi. You said it returned to zero, so it is probably not the scope. Shoot quite a bit more and see what happens.
     
  5. 4xforfun

    4xforfun Well-Known Member

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    Don't think so.....Lets assume for argument that he is shooting the 168 berger at 2600. You would need to drop down to under 2300 to lower impact points my 2.5 moa.

    Temp.... I max out my seirra program (130f to -30f) and am around 4 inches of change.

    There is not enough humidity on earth to make much difference at 500 yards.

    Also, if he is using a comp program to figure his come ups, he is probably already imputting the enviromental conditions.

    It is either a garbage in garbage out situation with the program or a scope issue.

    Just my .02
     
  6. sscoyote

    sscoyote Well-Known Member

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    Don't forget parallax--just another part of the checklist.
     
  7. RMulhern

    RMulhern Well-Known Member

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    Here's the cure: NIGHTFORCE!!
     
  8. Joe King

    Joe King Well-Known Member

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    SURE!!! you buyin?:D
     
  9. Codyg510

    Codyg510 Member

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    I’m shooting a 168 Amax handload with an average MV of 2642. I also shot Fed GMM 168 SMK as a standard with an average MV of 2533. I chose 500 yards as a good test distance because I can lay down accurate groups, but it’s still far enough to exemplify any defects.

    All conditions and factors considered the 168 Amax handload should require around11.25MOA of elevation compensation at 500 yards according to JBM and ballistic app. The 168 GMM should require approx 12.75 MOA of elevation adjustment with the same conditions. BTW, this is not angular shooting. My range is flat.

    When POA=POI I have to dial 13.75MOA for my Amax load and the equivalent increase from GMM.
     
  10. SBruce

    SBruce Well-Known Member

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    Very well could be the scope, especially if you've felt a noticable difference in how the dials rotate recently.......perhaps it's breaking in and your new click values are different than before.

    Just a thought, but any change in loading components recently? Different lot of primers, powder or bullets? Does the chrono show any big changes from previous muzzle velocity measurements?
    I be thinking it would have to be a big velocity change to equate to 13 inches of drop difference at 500 though. Plenty big enough that even a cheap chrony should show it.
     
  11. Greyfox

    Greyfox Well-Known Member

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    It sounds like it could be a scope issue. I have seen this type of effect when the scope is mounted so it is using the high end of the scope's elevation range, the turrets work, click, etc, but the scope does not track accurately and can actually repaet an elevation error consistantly. The scope will return to zero under this condition, but still have a problem. This can also happen if the elevator spring is defective, even if the scope is operating in the normal range. A good way to check this is to use a scope collimator with an MOA grid and examine the movement up and down your elevation range. If there is a problem, with this, or anything else involving scope tracking movements you will usually see it. At the very least, you can rule this issue out. 2.5MOA is a big shift, unlike to be caused by temperature or air density at 500 yards. The other thing that could cause this would be an ammo change. My son in law had this happen when he unknowingly loaded a couple of dozen reloads that had light powder charges by a couple of grains. This can also produce similar symptoms as the OP is seeing.
     
  12. JeffP40

    JeffP40 Well-Known Member

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    How in the world would click values change? I can see what greyfox is saying, but only if you are at the limits of movement. A bad spring is a maybe, but it is hard to figure it returning to zero every time.
     
  13. Greyfox

    Greyfox Well-Known Member

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    I'm by no means any kind of expert on scope mechanics, and it might not have been caused by the spring, but I had a Leupold that did not track in the midrange, but would return to zero. Leupold confirmed the problem and repaired it. It's on one of my rifles and works fine now.
     
  14. WildRose

    WildRose Well-Known Member

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    Think of two gears working together. When the notches on the gears get worn you get slack. You can also get the opposite if they are lubricated and thus the filings build up as can dust etc.

    With a worn spring you can also have a situation where you're not feeling some of the clicks as you are dialing.