Optically centering scope?

[Varminterror]

I've been trying to learn about optically centering my scope, which as I understand it is basically ensuring that my scope is pointing directly in line with my bore (left to right), eliminating drift along the range. For example, if my scope is pointed slightly RIGHTWARD compared to my bore, if I'm sighted in at 200yrds, then at 50yrds, the shots should strike to the right of my POA, and then at 500yrds, the POI will be slightly to the left of my POA.

To account for this, I have heard you need to optically center your scope, then adjust your rings/mounts to ensure lateral alignment, isolating the deviation between line of sight and bullet flight to one dimension (elevation), instead of two (elevation plus drift).

Alternatively, I could also believe you could test this deviation emperically, just as you test for and record elevation dope at different ranges. For example, a range card could show a zero wind value of 2MOA elevation, and 1/4MOA windage RIGHT for 500yrds, 6MOA elevation and 1/2MOA windage right for 1,000yrds, and -1/2MOA elevation at 50yrds and -1/8MOA left windage.

So what's the deal? Am I making a mountain out of a molehill and does the drift adjustment not matter that much, or do guys actually optically center their scope?

If so, how do you do it? The only way I can think is to roll my scope in the rings and see if the cross hairs scribe a circle, and adjust until they stay centered. But then how, without adjustable rings/mounts, do you sight in and zero your rifle while keeping the scope centered? Or do you just factor the windage adjustment into your range card?

 

[jo191145]

One neat trick for centering the scope before installation is hold it up to your Bathroom mirror on its lowest power setting. Tight up to the glass.
Look in it and you'll see two sets of crosshairs. Adjust until the two sets merge. Its now centered.

 

[Varminterror]

Great, that sounds like a cool trick! I'll have to play around with that this evening and try it out.

But then my next question is, once I have my scope optically centered, how do I mount and sight it in without taking it OFF center?

 

[4xforfun]

I've been trying to learn about optically centering my scope, which as I understand it is basically ensuring that my scope is pointing directly in line with my bore (left to right), eliminating drift along the range. For example, if my scope is pointed slightly RIGHTWARD compared to my bore, if I'm sighted in at 200yrds, then at 50yrds, the shots should strike to the right of my POA, and then at 500yrds, the POI will be slightly to the left of my POA.

To account for this, I have heard you need to optically center your scope, then adjust your rings/mounts to ensure lateral alignment, isolating the deviation between line of sight and bullet flight to one dimension (elevation), instead of two (elevation plus drift).

Alternatively, I could also believe you could test this deviation emperically, just as you test for and record elevation dope at different ranges. For example, a range card could show a zero wind value of 2MOA elevation, and 1/4MOA windage RIGHT for 500yrds, 6MOA elevation and 1/2MOA windage right for 1,000yrds, and -1/2MOA elevation at 50yrds and -1/8MOA left windage.

So what's the deal? Am I making a mountain out of a molehill and does the drift adjustment not matter that much, or do guys actually optically center their scope?

If so, how do you do it? The only way I can think is to roll my scope in the rings and see if the cross hairs scribe a circle, and adjust until they stay centered. But then how, without adjustable rings/mounts, do you sight in and zero your rifle while keeping the scope centered? Or do you just factor the windage adjustment into your range card?

I haven't got a clue what you are saying, or asking.

Do you want to center your crosshairs in your scope?.. The mirror idea is new to me, but sounds like a really neat trick. Otherwise, dial your scope all the way over to the left or right, and then dial back in the other direction and count the clicks. Dial back the other way half that amount. Then do the vertical (elevation) the same way...but always do the windage adjustment first.

Now you have a scope that has the crosshairs opticaly centered.

Now, if you are talking about centering your scope on your gun...which you should do AFTER you do the cross hairs,...that is a totaly differant deal, and depends on you gun/basses/ring setup.

We need more information on your equuipment. But everything you stated in your post was either so wrong that I couldn't follow, or I am an idiot!!!

 

[Varminterror]

One example: I just picked up a Savage 12 Benchrest 6.5x284. I'll be using Leupold 1 piece mounts and Leupold standard rings with a Zeiss Conquest 6.5-20x

When I installed the scope, I counted clicks up-down, and left to right, then counted them both back to the "middle". I lapped the rings, then set the scope in the rings (topless) and rolled the scope to ensure the cross hairs were ACTUALLY centered (was pretty close). I then leveled the reticle, and locked it down and bore sighted the scope. It was PRETTY close left to right, so I adjusted using the mount to keep the scope optically centered.

However, say i was using pic style mounts instead, or Nightforce 1-piece mount/rings, how would I sight in while keeping the scope optically centered?

 

[4xforfun]

As far as I know, you can't. They are where they are. If it is bad enough you will need to get adjustable bases, like the leupold with the windage screws on the rear rings. I can't rember the actual name of the basses....see ...I AM an idiot!!

 

[STP]

This is where the Burris Signature Zee rings with offset inserts come into play. I rarely can purchase a new scope theses days so the used ones I do get, I count the elelvation and windage numbers and write them down until I am satisfied I`m at "center" first. Then with the Zee rings and zero inserts installed, I try it on paper first. If there is a a great deal of correction needed I`ll use the 5, 10, or, god forbid, the 10 inserts to get the needed amount of correction w/o touching the elevation or windage knobs.

Most of need the extra "up" in order to gain the scopes maximum amount of elevation. (Minus the 10 or 20moa scope bases) The average scope has about 70 minutes total of up available, windage too. When mechanically centered, you have only 35 minutes of elevation and/or windage available afterwards.

The 30mm scope bodies have more, but the same thing applies.

A new scope out of the box is supposed to be centered from the factory. I suggest you confirm that first...trust, yet verify.

I have a `96 vintage Leupold Mark4 M1-16X I got used. Their catalog lists 140 minutes of elevation available and 45 minutes of windage. When centered as I described, mine has 142 minutes of elevation.

If your centered scope needs a noticeable amount of correction, the Burris inserts will help you get much closer to a zero. No, they are not perfect in terms of 5, 10, or 20 minutes adjustment. It will take some time on the range to find what works with your rifle. It`s like load data that`s often quoted for the same caliber in the same model rifle etc, etc....it doesn`t always reproduce the same results.

Regards,

Scott

 

[jo191145]

Leupold Standard bases. Sounds like what you have but.... Thats what 4x is referring too.
Burris Signature Rings STP referred to is the other option.


Mount it up centered and shoot it. See where it goes.
Even custom barrels do not always shoot to where bore sighting says they should.
I'm just a short range shooter. I used to worry about such things but for short range it does'nt matter much. Windage I try to keep centered if the equipment allows.
Vertical is whatever it is as long as I can shoot my rifle at the yardages I plan to shoot.

Wind and bullet drift are enough to mess up any calculations on windage at long ranges.
Thats just my stupid opinion ;D
Some long range shooters should have better knowledge than I.

 

[spclark]

Another trick was to take a small cardboard box & cut a V-notch in opposite sides. Place your 'scope across the notches, then slowly rotate while looking thru the eyepiece at a well lighted smooth surface like a white wall or bed sheet.

You'll note the point where the crosshairs cross will describe a circle. You need to rotate the two knobs until that circle is reduced essentially to nothing.

Then make sure when you install that scope that your rings are carefully aligned to put the axis of the scope parallel to the bore axis in the vertical plane.

Burris Z-rings help with this, and may also help you keep your scope as near center if you need some built-in elevation for longer distances.

 

[NateHaler]

So what's the deal? Am I making a mountain out of a molehill and does the drift adjustment not matter that much, or do guys actually optically center their scope?

Um, I think you should decide WHY you're interested in this, and then proceed accordingly.

The vast majority of shooters use a telescopic sight to hit their target better than they could without it. That's my goal too. So, I choose a scope with adequate internal elevation adjustment to enable me to get zeroed at my intended shooting distances. For 100y benchrest shooting, this is duck soup. For 100y-1,000y shooting, it's not so simple, i.e. you need to understand the ballistics of your load and pick a scope and rings/base that will work together.

Never once, in any of my rigs (numbering more than a couple of dozen over the past decade), have I concerned myself with what you've described. But we're all interested in different things, right?

I dial in the elevation adjustment. I dial in windage as necessary. (That changes, sometimes from shot-to-shot.) Then I shoot.

If you think you'll shoot better with a scope that is superbly aligned with the bore axis, then knock yourself out. But I think there are far better ways to spend your time.

 

[TonyR]

Tony Boyer recently published a very interesting book about benchrest shooting. One section deals with scope mounting including bedding the scope in the rings. He includes a discussion of how to do the "centering" as part of the process. Burris Z rings would probably be much easier but might not be OK for your purposes.

 

[artbosco]

I've been trying to learn about optically centering my scope, which as I understand it is basically ensuring that my scope is pointing directly in line with my bore.

If you mean by Optically or Mechanically centered, that the crosshair is residing in the center of the tube, then that's easy to do. Count the clicks from one end to the other of the Elevation or Vertical adjustment and then divide by two. The result will put you in the middle. Go to one end of the dial where it stops and count back until you reach half the total distance. Do the same for Windage.

To put the Mechcanically centered scope in the center of your rings you may have to bed it.

However, there's no need to have your scope pointing directly on line with your bore to hit Point of Aim. Here's an excellent explanation as to why you don't: http://practicalrifler.6.forumer.com/viewtopic.php?t=73

Also, don't forget that some Unlimited Benchrest Rifles [Rail guns] have their scopes offset quite a bit from the barrel axis and are some of the most accurate apparatuses' out there. Here's some pictures for viewing. Scroll down to see the offset: http://www.benchrest.com/magnummetal/

 

[jhord]

Varminterror, I understand what you're getting at, I have asked the question in the past too. Basically the answer is, like other people have suggested, adjustable rings. Center your scope before you mount it, then center your POI at your chosen zero range with the ring adjustments. (I use Leupold) I usually set up my rifle firmly in a rest, level it, then check scope level by aiming at a far off vertical target that you know is perpendicular to the horizon, (the corner of a new building, for example) then run the elevation adjustment on the scope up and down to make sure that tracks straight. You may have to go back and forth a few times checking the elevation tracking and readjusting your zero if you have to turn the scope. Then, armed with ballistics data from jbmballistics.com, go shoot the rifle on a perfectly still day at various ranges and note what the bullet is doing in regards to windage as you stretch out the distance. You can either roll your own dope card with the data, or adjust the cant of the scope to get things where you want them to be. Is it all worth it? I don't know. But I like the fact that on several rifles that I have done this with, I can shoot from 100-700yds on my home range and only have to worry about the wind and not any misalignments in the system. My windage zero is just that, zero, no matter what range.

 

[Samdweezel05]

Running your windage all the way left, all the way right, counting the clicks and then centering with half the total number of clicks is not optically centered, it's mechanically centered and does not necessarily mean the cross hairs are centered in the tube of the scope. Rotating the scope is the only real way to tell if the cross hairs are optically centered.

 

[Varminterror]

Thanks for all of the advice guys. I've known about the Burris Zee rings for a while, but I've been nervous to try them because I'm always a little wary about adding "parts" to the mounting system (more links in the chain). I have a new 6.8mm SPC AR rig that I'm building now that I'm thinking I'll order some Zee rings out on for a test drive.

One reason I like to ensure my scopes are at least CLOSE to optically centered above the bore is that many of my rigs are not dedicated target rigs and will see duty as hunting rifles, so I need the scope to trace accurately over a wide range. It's a nice luxury for my dedicated BR rigs to know once I get sighted in at a given range, I won't have much variation from there, but for example, one of my AR-15's sees action about once every month or two on paper, but probably twice a month all summer long on P-dogs. I usually only shoot 100/200yrd matches with the AR-15, but for P-dogs, I'll be shooting anywhere from 50-700yrds (occasionally farther), so scope drift isn't as much of an issue over the bench as it is over the field.

The other reason I like to ensure I did the best I could to eliminate varability is because I'm a professional engineer with a small case of OCD (haha), so I'm typically one to err on the side of caution and take extra steps even if they aren't big ticket items. Plus, I'm more of a "hobby shooter" and "casual competitor" and don't invest as much as I should in my rigs to reach the level of accuracy that I expect from them.

 

[Varminterror]

Another question about the Zee rings then...

Do you lap Zee rings? Since the inserts can pivot, do you need to lap the rings?

 

[jo191145]

Another question about the Zee rings then...

Do you lap Zee rings? Since the inserts can pivot, do you need to lap the rings?

Absolutely No lapping of Z rings.

 

[STP]

Another benefit to the Zee rings with the plastic inserts=

No ring marks

And they will not slip due to recoil. You must remove the preservative oil from the rings and inserts when you open the package. And wipe off the scope body prior to installing them.

Should you choose to trade, upgrade, or sell a scope that has had the Zee rings mounted later on, it`s much easier to do so. (Keep the rings!) :

Scott

 

[msinc]

The simple answer to this is covered already...you optically center the scope so you can have a starting point to make base adjustments {if you have adjustable bases, otherwise about all you can do is shim for elevation corrections} to allow maximum adjustment any way you might need to go for long range shooting. Which is of course where you might need it the most. I would like to add two points to this thread...first is that counting clicks gives you for certain a mechanically centered scope but not necessarily optically centered. What alot of folks don't realize is that you dont actually move the reticle. That is fixed and already centered. What moves is a washer that causes the shooter to "center" or aim at the right point. Kind of a bad way to explain that. True optical center can only be acheived by spinning the scope in V blocks and adjusting until the reticle center doesn't spin in a circle as covered previously.

The second point is that another reason to optically center a scope would be for absolute optimal light transmission. The less the washer is off center the more available ambient light gets straight to your eye...and the more you see at the edge of dark. Not a fix for less than perfect optical glass but for a given scope it is always best if the light goes straight thru.

I didn't know Zee rings allowed for sight in adjustments...it appears they are made so the one ring will positively align with the other. If this is the case then Zee rings wont help this topic at all.

 

[spclark]

I didn't know Zee rings allowed for sight in adjustments...it appears they are made so the one ring will positively align with the other. If this is the case then Zee rings wont help this topic at all.

That's true, in that their purpose is to add a means to correct for off-center ring mounting and / or +/- elevation when it's difficult to do otherwise by another method.

Maximum benefit is gained only with an optical sight that's been optically centered (explained here before) prior to installation.