Adjusting reticle vs. Adjusting mounting - Burris Zee rings

[Shootin4fun]

Someone posted the following comment on a product review site, and I'm interested in hearing what others think of what the author is saying about optical quality of scopes changing as we adjust the reticle towards the extremes.

"A little info. When you sight in a rifle scope in, you have to adjust the windage and elevation knobs. The more you "turn and click" the scopes reticle from its factory set "centered" setting with these knobs, you less clear and accurate the scope becomes. Picture a cross hair reticle in your scope. And imagine at its factory original setting you can "turn and click" the elevation and/or windage knobs 100 clicks each direction. You do this to line up and sight in the cross hair with you bullseye target. But, each time you move your reticle cross hair up/down/left/right from its original factory setting, your are moving the reticle toward the "sides" of the scope, when its better and more clear to have the reticle in the center of the scope. Now, what these burris rings allow you to do is instead of "click and turning" your elevation and windage knobs to the extremes where they are near the "sides" of the scope walls, you can FIRST adjust the scope using these plastic inserts that go between the metal rings and the scope. So lets say you shoot your rifle at the target, and your a foot high and a foot to the left. Instead of turning your windage/elevation knobs a foot each way, you put the corresponding plastic inserts in the rings to adjust the scope from the OUTSIDE of the scope, rather than internally. After you do this a few times you will be within say 4 inches of the bullseye, and NOW you adjust the final few inches using your elevation/windage knobs. And because you did very little "turn and clicking" of your knobs, your internal reticle is near the center of the scope (rather than the outside edges), and because of this it is more clear and accurate. Ask any scope expert, they will tell you in perfect world the reticle is near the center like it is when it comes from the factory. This Burris rings and inserts allow you to do this. I also recommend using a one piece base, preferably all steel (could run you 100 bucks for the steel one piece base, but its more accurate and strong). I use these rings on my Winchester 70 .270 and Rem. 700 30.06"

 

[trebark]

Wish I had more time to actually write out a more detailed response, but that quote is just crap.

 

[Dr. Vette]

Not sure what part of it trebark doesn't like, but yes it can work moderately similar to what is described in the quote. Note that the quote is almost verbatim what is said in Burris' own video.

The first time I used Burris Signature rings I was able to get my scope within 5 clicks (total) of being exactly "on" for a 200 yard point of aim. It took some shooting as well as trial and error, but I did it. Since then I've gotten a lot better at the process and it doesn't take nearly so much time. And, I have gotten subsequent scopes just as close - sometimes by intention and sometimes by luck.

Here is their webpade and video if you wish:
Scopes - rings by Burris Optics

 

[trebark]

There's no doubt the offset inserts can help to better align a scope (I use Burris Signature Rings on ALL my rifles). The part that is crap is an adjustment in the reticle would someone change the optical quality of the scope.

 

[Scot E]

Well, it wasn't worded very well but I think the gist of what he is trying to say is correct.

A scope is at its clearest when the turrets are close to centered. Additionally, turrets will be more consistent and precise near their center. I also believe a scope is more durable when the turrets are kept near center. That is a bit subjective I suppose but it surely can't hurt and with all the other benefits the signature rings are a no brainer IMO.

Burris signature rings are the real deal. They are an excellent product and I use them on just about everything I own. You can build in cant as well with them which eliminates the need for a canted base.

Scot E.

 

[Shootin4fun]

Yes, the part about optical quality changing at the scope's adjustment extremes is what I was really wanting to hear peoples' opinions about. I don't see why there should be a change in image quality when adjusting the retcile to the extremes and don't notice it on my scopes.

 

[Scot E]

Look through almost any pair of binoculars or a spotting scope and the clearest and brightest viewing area is the center. Even with high end models there is still a difference although it is much less noticeable. When a scope turret is cranked to the extremes the lens angle changes and the light path travels through the edges. This will impact the view to some extent depending on build quality, glass quality and coatings. I personally would be more concerned with the other issues that I mentioned that come from using scopes with turrets at their extremes.

Scot E.

 

[Dr. Vette]

Yes, the part about optical quality changing at the scope's adjustment extremes is what I was really wanting to hear peoples' opinions about. I don't see why there should be a change in image quality when adjusting the retcile to the extremes and don't notice it on my scopes.

Take a scope - any scope - and use a mirror to optically center the reticle:
Place the mirror on a sturdy table then place the scope on top of the mirror with the eyepiece up. Then look through the eyepiece and observe the image.
You will see the crosshairs and you should also see a reflection of the crosshairs as well (ghost image). All you have to do is to turn each of the knobs until they match up perfectly. If you can't see the reticles that well try placing a light near the mirror shining at its edge.

Now, take a cardboard box and cut a "V" notch in each end to hold the tube of the scope similar to where your rings would hold it. Rotate the scope on its axis while looking through it and notice the quality especially towards the edges.

For step 2 take the same scope and move one of the reticle adjustments to its limit. Move both adjustments to a limit if you want. Now place the scope back on the cardboard box and rotate it again on its axis. You'll now see a significant difference in optical quality from the first test and will understand why some try to keep a scope in the middle of its adjustment range whenever possible.

 

[bruce_ventura]

It's really a matter of degree (pun intended). It sounds like trebark is looking for a technical or at least plausible explanation, so here it is.

The objective lens on most scopes is a simple doublet achromatic design. This type of lens exhibits optical aberrations as the incidence angle of the light increases (i.e., as the viewing angle increases). As this angle increases, various aberrations, such as spherical, coma, field curvature, and off-axis chroma, will blur the image. Other aberrations, such as barrel or pincushion distortion, will cause the image to contract or expand. These effects become worse as the incidence angle increases. So, yes the image is clearer and the adjustments are more accurate near the center of the field of view.

For most scopes, the aberrations in the erector lenses are more noticeable than those in the objective. The erector aberrations are observed as you look from center to the edge of the field of view. The aberrations in the objective are difficult to "see" because the manifest themselves only as the elevation/windage knobs are rotated large amounts.

The first aberrations you will likely notice are field curvature and field distortion. Field curvature is a change in focus and can be removed by adjusting the AO or SF knobs. Field curvature causes an error in the adjustment at large viewing angles.

For viewing angles up to about 15 MOA, I have not been able to detect these aberrations visually on any but very cheap scopes. For viewing angles of 15-30 MOA (one-quarter to one-half a degree) the aberrations start to become visible to the trained eye. Above 30 MOA the aberrations become more obvious. At these angles image blurring occurs that cannot be corrected with the AO or SF knobs.

So, I recommend getting the scope tube axis aligned with the rifle bore axis to within +/- 15 MOA. This can be done with Burris Signature rings, or by using shims and windage adjustable bases. I also recommend using biased bases (or Signature rings) on long range rifles to minimize the elevation adjustment for long range shots.

FYI, in about a week HighPowerOptics will start renting rifle scope installation kits that allow you to align the scope to the rifle bore in this way.

 

[Shootin4fun]

This is all very enlightening, as I thought that in order to utilize the full range of adjustment of a scope for long range shooting (my scope only adjusts a total of 35 MOA), it would be best to mount it in such a way that a 100 or 200 yard zero would be at a very low elevation setting.
On the other hand I was concerned that a 20 MOA rail would raise the scope too much so that I couldn't adjust the reticle down far enough to zero at 200.

So I figured that a 0 MOA rail and Burris Zees which allow as little as 10 MOA would be a better option....I guess I bumbled into a good solution. Given that, what would be a good mounting position with respect to the scope reticle setting to zero at 200 if I need to go up 30+ moa to reach 1000 yards? If the reticle is set around 10 MOA for a zero at 200 wouldn't it run out of adjustment to reach 1000?

 

[bruce_ventura]

I recall that 30 mm Signature rings include two pairs of .010" offset inserts. Using both offset inserts will provide up to about 17 MOA of elevation bias (for rings separated by 4"). The set in the back raise the scope, while the set in the front lower it.

The 1" Signature rings come with no offset inserts, but i recall that the kit includes both .010" and .020" offset inserts. If so, then they will allow up to about 26 MOA of elevation bias.

Does your scope have 35 MOA or +/- 35 MOA of adjustment? If its only 35 (+/- 17.5), then you will need to shim your base as well to get the 200 yd zero at a scope elevation of 0-2 MOA from the limit of adjustment (the extreme bullet down limit). This would require an accurate boresight collimator, or a lot of time shooting at the range. You should also reduce your ring separation to increase the elevation bias available from the Burris rings.

If its +/- 35 MOA, then just use both .010 offset inserts to get 17 MOA of bias. Then you will have plenty of up adjustment for a 1,000 yd shot.

 

[Joe King]

Are you going to notice the difference on say.... a Vortex Viper or better scope?

The thing I would be worrying about would be inducing torque in the scope, Zee rings in theory should prevent that though.

 

[bruce_ventura]

Are you going to notice the difference on say.... a Vortex Viper or better scope?

The thing I would be worrying about would be inducing torque in the scope, Zee rings in theory should prevent that though.

Any scope below about $1,400 price point will probably have a simple doublet objective lens. Above that you can expect to see better objective designs in some, but not all scopes. I know that some Leica scopes, for example, use an air-spaced triplet objective design. Probably the high end Zeiss, Kahles and Swarovski scopes do as well.

I don't see how it's possible for Signature rings to stress a scope tube.

 

[Shootin4fun]

Does your scope have 35 MOA or +/- 35 MOA of adjustment? If its only 35 (+/- 17.5), then you will need to shim your base as well to get the 200 yd zero at a scope elevation of 0-2 MOA from the limit of adjustment (the extreme bullet down limit). This would require an accurate boresight collimator, or a lot of time shooting at the range. You should also reduce your ring separation to increase the elevation bias available from the Burris rings.

Thanks for all your feedback so far, guys.

The scope has a total of 35 MOA adjustment. The Burris ring set has the offset shims.

However I still don't have a full understanding of how a 20 MOA base or shims affect the impact point / reticle adjustment from 100 to 1000 yards. Furthermore there is the issue of adjusting a scope to its limits and the resulting effect on image quality.

So, let me understand. If I had a 20 MOA base OR installed 20 MOA ring shims on a set of high rings, and say the bullet drop at 100 yards is 2" @ 100, 8" @ 200 yards (similar to many calibers), wouldn't the impact point be too high even at the lowest reticle setting at 100? How many MOA from the bore line vs. sight line does that 2" or 8" bullet drop represent? (I supposed this is affected by the ring height - low med or high.) I bought a 0 MOA base (picatinny rail) because I was concerned I wouldn't be able to adjust down enough to zero at 100 or 200 if I used a 20 MOA base.

Next comes the issue of image quality when adjusting the reticle to extremes. If I do use a 20 MOA base or 20 MOA of ring offset shims, and then need to adjust the reticle down to 3 - 5 MOA from the scope's lowest setting for a 100 or 200 zero, how much image degradation will I incur? Much of my shooting is between 200 - 500 yards. Do I have to give up image quality for the ability to reach out to 1000 yards?

Up til now I have mostly used holdover to adjust for drop. The duplex post, or Nikon BDC. The Nikon BDC system has worked great for my most common conditions, but won't cut it for shooting over 700 yards. I've had a lot of fun chrono-ing my loads and programming them into the software, then seeing how that matches up to the physical reality of holdovers and impact points. Now I want to get into adjusting the reticle for distances.