Head scratcher question

BMF

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Jul 31, 2008
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Mid Michigan
My buddy has a full custom 338 Lapua with a 20 min ( also custom) picatinny rail and a night force atacr on it.

First thing he does is center the crosshairs ( even though nightforces come centered) both ways. Then, he bore sights his gun and zeros it at 100 yds for initial load development. He claims he should have to move his scope down 20 moa ( because he has a 20 min rail ) to zero it, but he only had to move it 10 min. This has been the same results on two separate nightfoces he's put on this gun.
Here's where we argue....haha~ He thinks they screwed him out of 10 minutes, and only made him a 10 moa rail. I know, I know....eye roll.
My argument to him is:
1.) The scope is 2.3" above the bore, CTC/ throws off the math a little
2.) The scope adjustments are behind the muzzle 30"/ throws off the math a little
3.) Your losing 2" ~in bullet drop from muzzle to Target at 100yds/ throws off the math a little
4.) Your crazy, and I can't do math, even a little...haha
Maybe he's right IDK. I just can't believe it's that simple. What do you guys think?
____________
Brent
 

The Oregonian

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I believe it is bc the scope has two spots where it is zeroed and neither is at the muzzle But that is a semi-educated guess. Interesting question.
 
Last edited:

Georgiashooter

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SMH. Tell him as long as the windage doesn’t have to be moved much to zero,the rifle is straight, don’t worry about the 10 moa he thinks he got screwed out of. All else will fall in place. Or if he’s not happy after that discussion tell him to cut a shim out of a beer can and place under his scope base to reclaim his 10 moa!!
 

MudRunner2005

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Alabama
My buddy has a full custom 338 Lapua with a 20 min ( also custom) picatinny rail and a night force atacr on it.

First thing he does is center the crosshairs ( even though nightforces come centered) both ways. Then, he bore sights his gun and zeros it at 100 yds for initial load development. He claims he should have to move his scope down 20 moa ( because he has a 20 min rail ) to zero it, but he only had to move it 10 min. This has been the same results on two separate nightfoces he's put on this gun.
Here's where we argue....haha~ He thinks they screwed him out of 10 minutes, and only made him a 10 moa rail. I know, I know....eye roll.
My argument to him is:
1.) The scope is 2.3" above the bore, CTC/ throws off the math a little
2.) The scope adjustments are behind the muzzle 30"/ throws off the math a little
3.) Your losing 2" ~in bullet drop from muzzle to Target at 100yds/ throws off the math a little
4.) Your crazy, and I can't do math, even a little...haha
Maybe he's right IDK. I just can't believe it's that simple. What do you guys think?
____________
Brent
You are correct. Your buddy needs to learn basic rifle mechanics before shooting LR at live animals. He needs to stick to steel while he learns the basics of LR shooting.

An easy way to prove you're right, is to teach him how to manually configured a proper drop-chart using all those crucially needed measurements. Because if you're measurements are not right, then your drops won't be right. And this will be easily proved on the range when he's shooting over or under his target, despite what his chart says.

Also, right-hand twist barrels (most all barrels) will cause some slight bullet drift to the right over dead-center, even at 100 yards. So a "dead-center" scope, is only good if you're 110% positive your action is 100% square to your barrel, your barrel's threads/lug shoulder are 100% square, the chamber is 100% cut square/true & perfect, that the bore in the barrel is 100% centered in the barrel, that your base screw holes are 100% centered to your action, that your base is 100% straight, and that your rings are 100% straight. And even if all these are perfect, you're just never going to beat the physics of gyroscopic drift of a bullet's mass spinning in a certain direction.
 

BMF

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Mid Michigan
SMH. Tell him as long as the windage doesn’t have to be moved much to zero,the rifle is straight, don’t worry about the 10 moa he thinks he got screwed out of. All else will fall in place. Or if he’s not happy after that discussion tell him to cut a shim out of a beer can and place under his scope base to reclaim his 10 moa!!
Haha, On both previous scopes he hasn't had to move the windage ( at least no more than a 1/2 min) and don't get me wrong, he's not mad. It's just the things we debate about over the winter.
 

Georgiashooter

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South Georgia
Haha, On both previous scopes he hasn't had to move the windage ( at least no more than a 1/2 min) and don't get me wrong, he's not mad. It's just the things we debate about over the winter.[/QUOTE

Yeah I couldn’t resist a little late night humor!! Lol.
 

Canhunter35

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Jun 13, 2017
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Most actions aren’t true on the outside, so the rail can only add to what the action is giving him in terms of a zero
 

Tom264

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Southern, Indiana
I’d be more worried about how much elevation I can get at max distance more than a measly 10 moa.
If it Max’s at 12-1300 and I only shoot to 1000 I’d not worry.
 

RockyMtnMT

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Have him put a zero moa rail on and see the diff. I have never paid attention to the amount of moa that I dial after putting on a 20moa rail but I am thinking it is usually about 10moa. I think you would have to zero the rifle with a flat rail to see the diff. I don't think I have ever put a centered scope on a rifle and had it shoot zeroed at 100y.

Steve
 

nmbarta

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billings mt
Most rifles drop somewhere around 2" @ 100.
Sight height is probably around 2", so if everything is perfect and the scope is centered he should be hitting around 4" low at 100 with zero moa.
add 20 moa (about 21" at 100) should put him about 17" high at 100, which is about 16 moa at 100.
so in a perfect world, he would have to dial his scope down about 16 moa to zero his rifle at 100. As mentioned above, there are several small factors that could change this.
I have no idea if this is right, that's just how it looks to me.
 

BMF

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Mid Michigan
Have him put a zero moa rail on and see the diff. I have never paid attention to the amount of moa that I dial after putting on a 20moa rail but I am thinking it is usually about 10moa. I think you would have to zero the rifle with a flat rail to see the diff. I don't think I have ever put a centered scope on a rifle and had it shoot zeroed at 100y.

Steve
Ha, that's funny because that's the exact same thing I told him.
 

TwoMore

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I may be wrong but the action is trued with the breech end of the barrel where the case is aligned with the bore not the muzzle, the muzzles differ between barrels as to how much runout or loft it adds. when you time an action you time that loft to 12 o'clock. the more loft the barrel has the more it affects elevation. have him set a flat rail on it and see. I pay more attention to wind-age on mounting a scope :)
 

BMF

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Messages
194
Location
Mid Michigan
I may be wrong but the action is trued with the breech end of the barrel where the case is aligned with the bore not the muzzle, the muzzles differ between barrels as to how much runout or loft it adds. when you time an action you time that loft to 12 o'clock. the more loft the barrel has the more it affects elevation. have him set a flat rail on it and see. I pay more attention to wind-age on mounting a scope :)
Yep, I agree about the windage. His windage has been right on with two different scopes.
I guess anybody could back-check how far they had to move their scope from center when they zeroed it. Just dial all the way up from zero, then dial all the way down from zero. Subtract the two numbers. Also subtract the minutes that it was zeroed at, ie 100, 200, 300 yds, ect. That should tell how far from center of the scope your zero is.
I think, haha......
 

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