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losing elevation when dialing

 
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  #8  
Old 09-12-2012, 01:24 AM
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Re: losing elevation when dialing

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  #9  
Old 09-12-2012, 02:14 PM
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Re: losing elevation when dialing

Iím 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 itís 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.
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  #10  
Old 09-13-2012, 04:24 AM
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Re: losing elevation when dialing

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.
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  #11  
Old 09-13-2012, 06:12 AM
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Re: losing elevation when dialing

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.
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  #12  
Old 09-13-2012, 05:38 PM
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Re: losing elevation when dialing

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.
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  #13  
Old 09-13-2012, 07:30 PM
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Re: losing elevation when dialing

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Originally Posted by JeffP40 View Post
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.
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.
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  #14  
Old 09-14-2012, 09:33 PM
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Re: losing elevation when dialing

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Originally Posted by JeffP40 View Post
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.
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.
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