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Could mirage cause my POI to be as much as 9-10" high at 600 yds?

 
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Old 04-14-2007, 08:21 PM
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Location: Mouth of Hobble Crk Canyon, Utah
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Could mirage cause my POI to be as much as 9-10\" high at 600 yds?

Here are the specs

30-06 Ackley, 180 Nosler 180 BT (.507 BC) at 3050 fps. Nikon 4.5-14x40 Buckmaster w/ mildot. 300 yd zero, level muzzle elev. 74 deg F. Sight height 1.8". 4960 ft Altitude. I had just shot 300, 400 and 500 yd groups prior to the 600 yd group. They were right on for altitude. The 600 yd group was into 4.75" but 9-10" high. 1/4 MOA clicks or 1.5" each click at 600 yds. Drop, according to
http://www.handloads.com/calc/
should be 46.83". I clicked up 32 clicks. My POI indicated I should have only clicked up 26 clicks.

Any ideas or suggestions? Could mirage have moved my POI up that far?
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Old 04-14-2007, 09:37 PM
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Re: Could mirage cause my POI to be as much as 9-10\" high at 600 yds?

GSSP
I hate to even respond to this question because it is a no win, some will disapprove of any response but here goes #1 get a scope that is repeatable a Leupold LR or a nightforce if you have no monetary boundarys. get a chronograph you can trust (not a chrony). and a good ballistic program like Exbal.
UB
ps mirage can make a difference no doubt but there are too many variables in this senario to call it mirage
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Old 04-14-2007, 10:21 PM
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Location: on the rifle range in Utah
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Re: Could mirage cause my POI to be as much as 9-10\" high at 600 yds?

Saw this exact thing on a student's gun last year with that exact scope. The problem was:

The scope dialed up the way it was supposed to through about 2/3 of it's travel then it suddenly started moving more than 1/4 moa after that and became more like 1/2 moa!

Solution:

Put several grid targets stacked vertically out at 100 yards and dial up and down on the grid with your crosshair and see if the value of a minute starts to change.

And as Unc B said, mirage and other things all could play into this scenario too.
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Old 04-14-2007, 10:57 PM
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Re: Could mirage cause my POI to be as much as 9-10\" high at 600 yds?

GG,

Thanks for the suggestion. Will try it ASAP. I have a friend coming out the 28th and we will be out towards Greely pass breaking in some new LVsteel and Hood flags.
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Old 04-18-2007, 07:05 PM
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Re: Could mirage cause my POI to be as much as 9-10\" high at 600 yds?

[ QUOTE ]
I was wondering if you might take the time to elaborate on some scopes increasing their MOA increaments as they move through their range. Ie, your reply here;

http://longrangehunting.com/ubbthreads/s...p;page=0#151303

Your post has me wondering if I need to upgrade to another scope. Anyway, if you can take the time to reply either here or on the site, I'd appreciate it. You said a students scope was doing this. I'm sure myself and others would appreciate more info on this.


GSSP
Near the mouth of Hobble Creek

[/ QUOTE ]




Sure. The truth of the matter is that most scopes do not track in even increments throughout their travel adjustments. Most start out moving what they are supposed to but when that erector spring starts getting compressed or loosened, some strange things can happen and the value of each click might change.

So, everytime I work with a new gun with/or a new scope, I put it on a grid and check it's travel. In my unique position, I get to see many different scopes and their capabilities. THere are two things I am looking for: click value uniformity and repeatability back to zero. Some scopes might have one and not the other and some have problems with both, and some have no problems at all.

For the most part, Leupold and Nightforce seem to be the best in my experience with both scenarios. I have seen a few Leupolds that went 1/4" through two revolutions and then suddenly increased slightly but they always returned to zero and were repeatable so that a drop chart could be altered to fit the change. I have not tested near as many Nightforce for these scenarios (probably 20 to 1 for Leupys)but I must say I haven't seen one yet that changed value.

Then there is everything else. All can work and all can have lemons. I will say that again: All scopes CAN work and ALL can have lemons. There is no point in debating scopes here, but the others just have a track record of having more problems from what I have seen and that is just my view from my standpoint (so please don't get all hot and bothered over this and start a flame session [img]/ubbthreads/images/graemlins/wink.gif[/img]) So that doesn't mean you can't buy a Weaver, or a Burris, or a Nikon and not dial it up. It simply means just checking it and correcting your drop chart if you notice a value shift.
I think all of those companies have good models and debating anything about a scope other than dialing capabilities is like debating what is the best color or the prettiest supermodel. [img]/ubbthreads/images/graemlins/wink.gif[/img]
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