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Need a little help with interpreting scope data

 
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  #1  
Old 05-15-2011, 03:22 PM
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Need a little help with interpreting scope data

In the past, I have mounted scopes and just leveled the crosshairs holding the rifle offhand. I do a pretty good job as will be seen below. Typically, I zero my deer hunting rifles 2" - 2.25" high at 100 yards which is dead on around 225 and 6" low at 300 (.280 Rem 140 BT). I have used it out to 325 yards and feel comfortable shooting a bit farther than that using holdover. I shoot highpower and feel very confident about 1st round hits to at least 600 yards with adjstible turrets so I decided to rig my rifle better for the task. I received a 3.5-10x40 Leupold CDS with a plex crosshair as a gift and sent it back to Leupold to install a CDS windage turret. After reading about how some of you guys check the installation of your scopes, I tried the following experiment:

I used a blank piece of paper at 100 yards. Using a level, I drew a vertical line 18" long. I thin drew a horizontal line to form an upside down "T". I shot my rifle on my 100 yard zero (needed a bit windage to get it centered). To save a bit of time and most importantly barrel heat, when it looked centered, I added 15 MOA and fired 2 more shots. As you can see from the attached picture, the center of my 100 yard group was about .3" left of centerline and the +15 MOA group was on the centerline. If you drew a parallel vertical line through the lower group, the center of the upper group is .2" from the parallel line.

Here are my questions:

1) Is this deviation within acceptable tolerances for shooting out to 600 yards? Or should I try to turn the scope in the rings to correct it?

2) I have been experiencing an odd phenomenon. When My scope is zeroed for 100 yards, I get some horizontal (still well under MOA). When I add elevation 9 - 15 MOA, I always end up with all shots touching. One day I even did this alternating shots between zero and +9 MOA. Weird. Anyone care to comment?

Rifle is a McMillan Signature. 24" #3.5 barrel (Rem mag profile) with Burris Weaver style mounts and Burris low 1" Zee rings.

Any comments appreciated.

Dan

PS Those are two 2 shot groups with a 1/4 MOA right wind correction between them.
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Need a little help with interpreting scope data-.280-scope-1.jpg  

Last edited by DZelenka; 05-15-2011 at 03:33 PM.
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  #2  
Old 05-15-2011, 04:20 PM
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Re: Need a little help with interpreting scope data

Are you using a bubble level when shooting?
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Old 05-15-2011, 04:26 PM
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Re: Need a little help with interpreting scope data

Quote:
Originally Posted by BuckSnort View Post
Are you using a bubble level when shooting?
No I am not, but the horizontal and vertical crosshairs were aligned with the horizontal and vertical lines on the target which had been drawn with a level. That should make the scope level when fired.
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Old 05-15-2011, 05:01 PM
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Re: Need a little help with interpreting scope data

Quote:
Originally Posted by DZelenka View Post
No I am not, but the horizontal and vertical crosshairs were aligned with the horizontal and vertical lines on the target which had been drawn with a level. That should make the scope level when fired.

Scope would have been leveled yes but that doesn't mean the scope is leveled with the rifle... How did you mount the scope?
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Old 05-15-2011, 05:43 PM
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Re: Need a little help with interpreting scope data

Quote:
Originally Posted by BuckSnort View Post
Scope would have been leveled yes but that doesn't mean the scope is leveled with the rifle... How did you mount the scope?
I just eyeballed it. 35 years of doing that puts me pretty close.

The test that I did is to determine the levelness of the scope. If the scope is not level to the rifle, when you raise the elevation 15 MOA, if the scope isn't level to the rifle, it won't track in a straight vertical direction. My question is more about whether I need to turn the scope clockwise slightly to remove the slight horizontal tracking to the right when I raised the elevation. Perfect would be great, but I am trying to determine what experienced long range hunters find acceptable.
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Old 05-15-2011, 05:48 PM
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Re: Need a little help with interpreting scope data

Unless you mount it to the rifle compleately level you're gonna be chasing you're tail trying to get things perfect..
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Old 05-15-2011, 06:11 PM
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Re: Need a little help with interpreting scope data

For 15 MOA of adjustment that is pretty good. It would be a pretty small adjustment to try and get that angle of degree out. You could try but might not make it back to where you are now. Now the real test shooting it at 600 yards. This will show you your spin drift and a new factor to adjust for. As for the dispersion left to right at your zero. Does it do it through the whole adjustment? At 8 MOA is it half as big of group? If it were bedding or an issue with the rifle you would see it throughout the adjustment. It might be an issue with the scopes erector setup.
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