0 vs. 20 moa base

[foxx]

You may be right, bflee. But if so, Burris' claim to promote their Z-rings is non-sense (I don't think it is, though). They say you should first center your reticle mechanically, then use their adjustable rings to aim your scope as close as possible before making the final adjustments with the scopes adjustable reticle. Their reasoning is this allows you to use the best part of your lens for aiming, or whatever. If I understand them correctly, they are suggesting the angle of the mount affects what part of the lens you use.

[foxx]

I thought the reason I would want a cant is to allow me to use a greater portion of the scope's adjustment range, rather than just the lower part. i.e. with the cant, the scope points downward, forcing me to use the upper part of the its adjustments for close range. Normally, that part is "wasted" if mounted parallel to the bore. When I do so, I am utilizing the outer edge of the lens. Ideally, I want the scope mounted so I am using the best part of the lens (the center) at the distance I most normally shoot, but that is not possible if I shoot at all ranges, so I must compromise somewhere. The question becomes, where is image quality most critical.

Right?

[bflee]

Your reticle will not move enough to get you out of the "center" of your optic. You will notice no difference in your glass, just your adjustment range. If you can still zero at your shortest range you have lost nothing.

[foxx]

I don't know if that is correct or not, I guess. I thought when you moved your reticle to extremes, you were moving it outside the center of the lens.

Maybe not.

Is there anyone here that knows for certain?

[bflee]

Do you ever look into your scope after adjustments and the horizontal center reticle looks like it is anywhere but center? If you do you need a new scope! I make lenses for a living. Trust me, it is moving, but not enough to get you too far off center.

[foxx]

That's the answer I was looking for! It IS moving, but not as much as I was worrying about. :)

Thanks.

I suppose being a pro, you also were correct about clarifying the use of terms such as "optically" centered vs. "mechanically" centered. :)

Gotcha. :)

[foxx]

Bflee, would my concern be warranted if I relied on the upper-most "mark" on the verticle reticle for my close-range shots? i.e. is that portion of the reticle still fairly close to the center of the lens, or is it far enough away to be concerned? (not that anyone would ever use it that way, just testing my understanding of how they work).

[bflee]

That may be more of a concern depending on what scope you have. I was referring to the center. Most scopes these days have an etched glass reticle. That means if you move your reticle, the center of optics goes with it. The bottom verticle will depend on the grade of your glass. If you can see good down there use it.

[chukarmandoo]

Foxx, If you have a ffp type scope and you turn it down to its lowest setting you will see that the reticle is very small and centered even with a 20 moa base. Even a scope with 100 moa adjustment moves very little. Measure your 20 moa base and you'll see its only a few thousandths of an inch from front ring to rear ring. I've heard that the windage is more affected than anything else when using the upper or lower limits of a scope but I have never experienced that either and I've shot in some very bad wind at long ranges.

[foxx]

cool. thanks.

My wife tells me I over-think stuff sometimes. My "what-if" thinking can take me beyond the realm of practical reality. Maybe she's right. :)

Yes, the sun will die-out some day, but who cares!?

[bflee]

Your reticle lens is actually a tube within the outer tube of your scope. When you adjust the reticle the lens actually moves, so you are still looking through the center of the lens optically. That being said, if you have to adjust it too far out of mechanical center to sight it in vertically, it does effect how far you can adjust windage. Think of it as a tube within a tube and you will understand. If it has to go up or down out of center it limits your travel left to right because the outer tube is smaller at the top and bottom.

[foxx]

got it. Thanks again.

[yobuck]

Your reticle lens is actually a tube within the outer tube of your scope. When you adjust the reticle the lens actually moves, so you are still looking through the center of the lens optically. That being said, if you have to adjust it too far out of mechanical center to sight it in vertically, it does effect how far you can adjust windage. Think of it as a tube within a tube and you will understand. If it has to go up or down out of center it limits your travel left to right because the outer tube is smaller at the top and bottom.

So if im following all this correctly, without a tapered base Foxx here will run out of elevation adjustment before his 308 reaches 1000 yds.
And since he used up all the elevation, he will also be out of windage because of the shape of the scope tube?
I must admitt ive never experienced or tested this theory.
Im told holding a mirror in front of the scope will reveal this, but ive never tried it.
Also FOXX could use rings with inserts like burris for example and get by just fine with his 0 base.
I believe he could also use those to help with centering the windage.

[bflee]

You are correct Yobuck. I do t know about the mirror trick!
A canted base will not effect your optics in any way. It will effect where the mechanical center is. In the mechanical center of your scope you will have more windage adjustment. Bottom line is: if you shoot long range you need a canted base that will get you there and keep your scope close to the middle vertically so you can adjust the windage at thise ranges also. Using a canted base will not be an issue up close as long as you can set your zero where you want it. Windage is not an issue as much at the short ranges.

[yobuck]

You are correct Yobuck. I do t know about the mirror trick!
A canted base will not effect your optics in any way. It will effect where the mechanical center is. In the mechanical center of your scope you will have more windage adjustment. Bottom line is: if you shoot long range you need a canted base that will get you there and keep your scope close to the middle vertically so you can adjust the windage at thise ranges also. Using a canted base will not be an issue up close as long as you can set your zero where you want it. Windage is not an issue as much at the short ranges.

Well today tapered bases for long range are a given. The option would be inserts in the rings which accomplish the same thing.
Realize also that as recent as roughly 25 years ago none of these things existed in the market place.
Shims were made for that purpose from beverage cans. Also many hunters simply hold over for wind without dialing.
Especially on follow up shots.

[bflee]

Yep. Thats the beauty of the new rails! Carry the cans to the recycle center!

[chukarmandoo]

I was givin a Mauser action that had been timed & trued. bolt handle was redone and it was drilled and taped for a Leupold base. When I finished the rifle I shimmed the base with coke can shims. I might be able to get another base for it but this works fine.

[foxx]

So...

I needn't worry about optical quality changing at the extremes of a scope's adjustment range.
I most likely will NEED 20 MOA base for long range, no matter what.
If 20 MOA doesn't allow for close range zero, and it turns out I don't shoot long range, I can fix that with Burris Z rings.
If later I DO shoot long range, the Z rings allow me to adjust for it, assuming I have 20 MOA base to begin with.

Sounds like the best, most versatile arrangement is 20 MOA base with Burris Z rings.

[Hotolds442]

I just picked up a new Zeiss Conquest 6.5-20, and in the owners manual it states: "To be able to use the full range of the elevation adjustment, the riflescope should be mounted on the rifle at an angle of approx. 20 angular minutes with commercially available mounting systems (corresponds to 21 inch/100 yards or 58.4cm/100m)."
I installed an EGW 20moa base, and my 2" high at 100 yards is as low as the scope will go, giving me a perfect zero stop for elevation.

[stewart3]

I run a 20moa base bedded to my 7mag with a Leupold topped on Burris sig zees. My zero is 100yds. I believe my scope has 52moa adjustment. A couple weeks ago I shot a 1000yds, ammo chronographed to 2950fps with berger 168gr vld at 1550amsl. Calculator gave -259.57'' bullet drop. I had 30 moa in elevation adjustment left and still I was approx. 40'' low at that range. My point is that 20moa may not be enough to go out that far without additional shimming or optic adjustment. I will be using the offset inserts myself, convenient for sure, zero at long range and adjust down to close range.