Flat or 20 MOA scope base for 308 Win out to 1000

atl5029

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Oct 2, 2014
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Dayton Ohio
Hi all,

I want to put a 1 piece picatinny scope base on a 308 and I was wondering if a 20 MOA mount would really be necessary. I would be shooting a 20" 1:10 twist barrel with 165-180 grain bullets. Would likely never take it much past 1000, and most shots would likely be 800 and in. Then again, I tend to understate what I intend to do lol.
 

mtwarych

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Aug 16, 2013
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Stevensville MT
I have a 20" semi-auto 308 without a 20 moa base on it.
According to a ballistic program, zeroed at 200 yds, I would be able to dial up to 1040 yds.
After dialing up, I could use holdover, but I think I will purchase a 20 moa base for the rifle.
 

ShtrRdy

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Jan 14, 2012
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High Plains
If your scope has the verticle range, it would be good to use some of the other half by mounting it on a 20 moa base.
 

Mateo

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Feb 3, 2014
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Depends a lot on what scope you use. You need 35-40 minutes of adjustment past your zero.
 

atl5029

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Oct 2, 2014
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Location
Dayton Ohio
Scope would be a 6-24x mil dot which will eventually be upgraded to a vortex of same power. Thanks for the quick replies. I think I'll go with the 20 MOA.
 

FEENIX

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Dec 20, 2008
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Great Falls, MT
Hi all,

I want to put a 1 piece picatinny scope base on a 308 and I was wondering if a 20 MOA mount would really be necessary. I would be shooting a 20" 1:10 twist barrel with 165-180 grain bullets. Would likely never take it much past 1000, and most shots would likely be 800 and in. Then again, I tend to understate what I intend to do lol.

From a optics SME ...

Even though the scope adjustment range may be large enough to get to 1,000 yds, you should use a 20 moa base. That's because off-axis optical aberrations that degrade resolution increase with incidence angle. You should set up your rifle so that the incidence angle is minimized for long distance shots (where resolution matters most).

Assume the base is within +/-10 moa of alignment with the rifle bore. Let's also assume your bullet drops no more than 30 moa at 1,000 yds, and you like to zero your rifle at 100 yds. With a standard base, you would need up to -40 moa of adjustment to get to 1,000 yds. That means you need a total 80 moa of adjustment.

With a 20 moa base you would need up to -20 moa to get to 1,000 yds, but up to 26 moa to get to a 100 yd zero (worse case boresight alignment in each case). That means you need a total 52 moa of adjustment. With a 20 moa base, however, the incidence angle at 1,000 yds is 20 moa less, so the image will have less blur.
 

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