Scope mounting with Burris inserts

[mousegunner]

My rifle scope was bottomed out and the cross hairs were still 5 inches high at 100 yards. This was on an AR with the "0" inserts.

I have the different height inserts on hand, so do I need to lower the front of the scope and raise the rear to get the cross hairs down? I did find some Burris instructions but the printed instruction and diagram seemed opposite of each other.

Anyhoo I centered the cross hairs within the tube and just need to figure out what inserts to use. I am going to shoot this anywhere from 75 to 300 yards but mostly 100-200.

I did call Burris but they didn't respond, it was late in the day though.

As always thanks for looking and your feedback.

 

[MattPeetz]

Yes. You have it correct.
Just remember to use the opposite pair in back.
Example.
you have -.010 on bottom front ring halve and +.010 on top front ring halve

back rings should be +.010 on bottom ring halve and -.010 on top ring halve.
Don’t use zeros on back and the -.010 and +.010 up front. Keep same number sets.
You could use zero’s on the back but run risk of it not aligning right. Some have had success doing it that way and some not.

 

[mousegunner]

O.K. Then I need some more .10 rings, I have 2 of each .05, .10 and .20 in the -/+ range. I suppose I could use the .05 or .20 but then I'd go not high enough or too high.

 

[nksmfamjp]

Well, yes you need to raise front, lower rear if I read you right. So, with the scope centered, how many inches are you off in vertical? You can get up to 40 moa shift with these rings!

 

[mousegunner]

My crosshairs were 5 inches high above the center X at 100 yards.

 

[204 AR]

I'll throw in here, I use these rings alot. Lower the front, raise the rear, it sounds like you need quite a bit. I'd try the 20 and the 10. I've used them in every combination, even used them side ways and kitty-cornered to move the scope where I wanted to center it up. They always worked for me.

 

[MattPeetz]

If you are 5 inches high. You need to raise the front.

 

[204 AR]

He said his cross hairs are high, not his bullet holes. He needs to lower the front of the scope.

 

[KY_Windage]

Move the front of the scope to your point of impact ("POI"). If your POI at 100 yards is lower than where your crosshairs are pointing, move the front of your scope down (or the rear of your scope up, or both).

A good rule of thumb is that if you change the inserts from "0's " to "10's," you will move your POI about 10 moa, which is close to 10" at 100 yards.

 

[KY_Windage]

My crosshairs were 5 inches high above the center X at 100 yards.

I would also suggest you quit talking about your "crosshairs" being high. If your crosshairs are high you lower your front rest or raise your rear rest until your crosshairs are on the bullseye.

Hold your crosshairs on the bullseye, then shoot and tell us where your POI is, e. g. above the bullseye or below it, etc. Then we will know what you are actually talking about, instead of trying to guess at what you mean.

 

[mousegunner]

My crosshairs were 5 inches high above the center X at 100 yards.

Mea culpa, mea culpa. In my haste to write my opening post I forgot to say that I was bore sighting this rifle. My bull was centered in the bore but my crosshairs were sitting 5 inches high with the elevation turned all the way down.

I never did fire a shot since I couldn't bore sight and set it aside for another time. My main focus that time was on another rifle so I worked on it.

Now I have bore sighted a rifle before, my 40x, AR15 carbine, .22 bolt action Ruger, various M4 carbines with and without a laser boresighter. This is the first time I've had this problem. This AR does have a squared upper receiver and used to have match open sights, which I also bore sighted, and sighted in no problem.

Anyhoo I'll change the inserts and wait for the next time I go to the range. Till then thanks for the input, as always I learn a lot from you guys.

 

[Robbie610]

Maybe I'm missing something. If the bore is pointing 5 inches below the crosshairs at 100 yards, the POI should be about 5 inches low. Because that's where the barrel's pointed relative to where the crosshairs are. The OP says he has the scope dialed all the way down (elevation knob fully clockwise on most scopes). Which means he has it adjusted for the lowest possible POI. Scope adjustments are for adjusting POI, not POA. If he adjusted the elevation knob 5 moa upward, while holding the rifle steady and looking through the scope, he should see the crosshairs appear to move downward and coincide with the placement of the bore. The turrets don't move the crosshairs, which are fixed in place. They move the erector tube, which is why the crosshairs appear to move in the opposite direction of the turret adjustments while holding the gun still. So, he probably doesn't actually need to use the offset inserts to zero the gun at 100 yards. But it sounds like he has a problem anyway. If the scope is in the center of its adjustment range (maybe as much as 20 or 30 moa higher POI) his crosshairs will be well below the target, while the bore is centered on it, and his shots will impact very high, not very low. I'd like to hear what he sees through the bore and scope with the crosshairs in the middle of their adjustment range.
He won't be able to use the offset inserts, as they're designed to be used, until he centers the crosshairs in their adjustment range and has some idea of the difference between POA and POI. With the offset inserts, he needs to move the front or rear of the scope, or both, so the scope is pointed to the POI.

 

[MattPeetz]

Maybe I'm missing something. If the bore is pointing 5 inches below the crosshairs at 100 yards, the POI should be about 5 inches low. Because that's where the barrel's pointed relative to where the crosshairs are. The OP says he has the scope dialed all the way down (elevation knob fully clockwise on most scopes). Which means he has it adjusted for the lowest possible POI. Scope adjustments are for adjusting POI, not POA. If he adjusted the elevation knob 5 moa upward, while holding the rifle steady and looking through the scope, he should see the crosshairs appear to move downward and coincide with the placement of the bore. The turrets don't move the crosshairs, which are fixed in place. They move the erector tube, which is why the crosshairs appear to move in the opposite direction of the turret adjustments while holding the gun still. So, he probably doesn't actually need to use the offset inserts to zero the gun at 100 yards. But it sounds like he has a problem anyway. If the scope is in the center of its adjustment range (maybe as much as 20 or 30 moa higher POI) his crosshairs will be well below the target, while the bore is centered on it, and his shots will impact very high, not very low. I'd like to hear what he sees through the bore and scope with the crosshairs in the middle of their adjustment range.
He won't be able to use the offset inserts, as they're designed to be used, until he centers the crosshairs in their adjustment range and has some idea of the difference between POA and POI. With the offset inserts, he needs to move the front or rear of the scope, or both, so the scope is pointed to the POI.

do you make everything in your life difficult?
it’s not that hard.
The reticle does move because it’s in the erector tube.
Even though your barrel is centered on the target does not mean it’s hitting there. It will only hit that spot within inches of the muzzle because the bullet starts dropping as soon as it leaves the barrel.

Oh, and I didn’t read it all as it was run on sentences. Some paragraphs would make it easier reading.

 

[Robbie610]

Maybe I'm missing something. If the bore is pointing 5 inches below the crosshairs at 100 yards, the POI should be about 5 inches low. Because that's where the barrel's pointed relative to where the crosshairs are. The OP says he has the scope dialed all the way down (elevation knob fully clockwise on most scopes). Which means he has it adjusted for the lowest possible POI. Scope adjustments are for adjusting POI, not POA. If he adjusted the elevation knob 5 moa upward, while holding the rifle steady and looking through the scope, he should see the crosshairs appear to move downward and coincide with the placement of the bore. The turrets don't move the crosshairs, which are fixed in place. They move the erector tube, which is why the crosshairs appear to move in the opposite direction of the turret adjustments while holding the gun still. So, he probably doesn't actually need to use the offset inserts to zero the gun at 100 yards. But it sounds like he has a problem anyway. If the scope is in the center of its adjustment range (maybe as much as 20 or 30 moa higher POI) his crosshairs will be well below the target, while the bore is centered on it, and his shots will impact very high, not very low. I'd like to hear what he sees through the bore and scope with the crosshairs in the middle of their adjustment range.
He won't be able to use the offset inserts, as they're designed to be used, until he centers the crosshairs in their adjustment range and has some idea of the difference between POA and POI. With the offset inserts, he needs to move the front or rear of the scope, or both, so the scope is pointed to the POI.

 

[Robbie610]

OK. I'm assuming his scope is the same type as most of them. Second focal plane, externally adjustable. If so, the reticle is not in the erector tube. It doesn't move when you turn the adjustment knobs. Instead the front of the erector tube moves up, down, left, or right while its rear end rotates around a universal joint. Its movement changes your view of the target area, while the reticle stays still. That's why, if you hold the gun still and dial in elevation and windage adjustments, the reticle appears to move in the opposite direction of the way you move the adjustments. If the reticle were in the erector tube it would move in the same direction as the tube does. Try it yourself.
I wasn't trying to make it hard. And I apologize if there were run on sentences. But I'm mainly interested in knowing if my analysis of the OP's problem is correct.

 

[MattPeetz]

OK. I'm assuming his scope is the same type as most of them. Second focal plane, externally adjustable. If so, the reticle is not in the erector tube. It doesn't move when you turn the adjustment knobs. Instead the front of the erector tube moves up, down, left, or right while its rear end rotates around a universal joint. Its movement changes your view of the target area, while the reticle stays still. That's why, if you hold the gun still and dial in elevation and windage adjustments, the reticle appears to move in the opposite direction of the way you move the adjustments. If the reticle were in the erector tube it would move in the same direction as the tube does. Try it yourself.
I wasn't trying to make it hard. And I apologize if there were run on sentences. But I'm mainly interested in knowing if my analysis of the OP's problem is correct.

You are correct on erector and reticle. You are over thinking it. The inserts will correct the problem.
The front of the scope will drop lowering reticle.
Your letting the reverse movement mess with you.
The reticle will drop when using the inserts.

 

[BoydAllen]

A couple of corrections with a picture: In this article

Inside Look — Cutaway Weaver Scope Reveals Complex Internals « Daily Bulletin

Based on its external appearance, a modern riflescope may seem simple. It's just a tube with two or three knobs on the outside right? Well, looks can be deceiving. Modern variable focal-length optics are complex systems with lots of internal parts. Modern scopes, even 'budget' optics, use...

bulletin.accurateshooter.com

there is a cutaway of the eyepiece and back of the scope. If you look carefully you will see a blackened brass section that is attached to the erector tube behind the spherical erector tube pivot system.
The part behind the blackend part that (contains the reticle) is a baffle. From this, you can see that the reticle is part of the erector tube.
With regard to which way you have to adjust the turrets to bring the reticle to a point on the target one needs to remember that before the erector tube does its job the image is inverted, hence the name erector tube (It turns the image right side up.). If you imagine a picture of a target on your computer's screen that is upside down, with you looking at the center, you would have to raise your eyes to look farther down on the target and the reverse to look up. That essentially is what you are doing with the erector tube and turrets.

Finally there is the mater of which way the scope is tilted to make the cross hairs come to a bullet hole that is higher than where the scope originally pointed. You have that exactly backwards, (unless I got in too big of a hurry reading). Imagine that the rifle barrel is locked in a vise pointing at the bullet hole. Since the scope is pointing below that, given that you are not using the turrets to make the correction, but rather the scope rings, you would have to raise the front of the scope, assuming that you were pivoting it at the back ring, to make the cross hairs come up to where the barrel is pointing.

Canted scope bases that are used to give more vertical adjustment range above a given zero, are thicker at the back than the front, which makes the scope tilt down a little in front. In the case of a 20 MOA base 20/60 equals 1/3 degree.

 

[KY_Windage]

Mea culpa, mea culpa. In my haste to write my opening post I forgot to say that I was bore sighting this rifle. My bull was centered in the bore but my crosshairs were sitting 5 inches high with the elevation turned all the way down.

I never did fire a shot since I couldn't bore sight and set it aside for another time. My main focus that time was on another rifle so I worked on it.

Now I have bore sighted a rifle before, my 40x, AR15 carbine, .22 bolt action Ruger, various M4 carbines with and without a laser boresighter. This is the first time I've had this problem. This AR does have a squared upper receiver and used to have match open sights, which I also bore sighted, and sighted in no problem.

Anyhoo I'll change the inserts and wait for the next time I go to the range. Till then thanks for the input, as always I learn a lot from you guys.

As noted, "bottoming out" your E turret, as in turning it clockwise all the way, makes your reticle high relative to your POI (which is close to the same as your bore sighting). So you may just need to turn it counterclockwise to sight in.

However, I will say that what you have (apparently) done is what I usually do -- I crank my E turret almost all the way down and then use the Burris inserts to move my scope to where I am sighted in. That leaves me nearly the full amount of internal adjustment available for shooting at long range.

 

[LeeA]

Mea culpa, mea culpa. In my haste to write my opening post I forgot to say that I was bore sighting this rifle. My bull was centered in the bore but my crosshairs were sitting 5 inches high with the elevation turned all the way down.

I never did fire a shot since I couldn't bore sight and set it aside for another time. My main focus that time was on another rifle so I worked on it.

Now I have bore sighted a rifle before, my 40x, AR15 carbine, .22 bolt action Ruger, various M4 carbines with and without a laser boresighter. This is the first time I've had this problem. This AR does have a squared upper receiver and used to have match open sights, which I also bore sighted, and sighted in no problem.

Anyhoo I'll change the inserts and wait for the next time I go to the range. Till then thanks for the input, as always I learn a lot from you guys.

All you need to do is turn your elevation turret dial "UP" 5 inches!