Scope Rings vs 20 MOA rail

[Qbeam]

Do high scope rings achieve the same effect as a 20 MOA rail on a rifle? I under stand the benefits of the scope rail when changing scopes between rifles, but if a scope was to be dedicated to a rifle, would the rail be necessary?

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[kalister1]

The 20 MOA rail is designed to tilt the scope for long range shooting. If the high rings are both the same height, they will not have the same effect.

 

[DutchV]

Burris Signature rings have inserts that can be changed and adjusted to give a bit of angle to the scope. It would save you from needing an angled scope base.

 

[Qbeam]

So it is the tilt and not necessarily the height that give the extra elevation?

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[Russ D]

Correct

 

[Qbeam]

Thanks guys, good information. I'm waiting for Yoda to chime in with the in depth answer. Hopefully he chimes in with his usual wisdom which is always a learning experience.

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[E.Shell]

So it is the tilt and not necessarily at all the height that give the extra elevation?

Q

FIFY.
Russ is correct.

 

[Qbeam]

LOL, thanks Yoda.

 

[Qbeam]

When does 20 MOA rail come into practical application? For shooting 308 and 223, out to 600 yds, would it be needed? What yardage would you need to start considering it?

Q

Sorry for the follow on question.

 

[atblis]

Depends on the scope. Some have more adjustment.

 

[jimbobborg]

When does 20 MOA rail come into practical application? For shooting 308 and 223, out to 600 yds, would it be needed? What yardage would you need to start considering it?

Q

Sorry for the follow on question.

The 20 MOA rail is for long distance. 600 yards is not long distance

 

[BradMacc82]

The 20 MOA rail is for long distance. 600 yards is not long distance

Well what if he's shooting 22lr???

Then I'd say 600 would qualify for long distance.

 

[atblis]

The point of the 20 MOA rail is to bias your scope adjustments such that you gain 20 MOA of adjustment. 308 drops about 15 MOA at 600 yards and 35 MOA at 1000 yards. Most scopes have enough to get you to 600 yards with no special bases needed.

For example, the Zeiss Conquest 4.5x14x44 has about 65 MOA of elevation adjustment. If you're lucky enough to start with the scope centered (often not the case), that gives you ~32 MOA to work with. That'll get you to 600 yards. Now, at 1000 yards you might need that 20 MOA base. While optically and mechanically a decent scope, it is not the best choice for long range shooting.

Another example is the Sightron 10x42 SIII. It is advertised as having 150 MOA of adjustment. No 20 MOA base needed.

 

[Qbeam]

Fellas, Fellas, just trying to get a discussion going, lol. With all the "tacticool" items out there, just wanted to discuss need to have, versus nice to have.

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[INMY01TA]

May as well use a 20moa rail as it doesn't hurt you to have it. Might not want it now but maybe later.

 

[E.Shell]

The 20 MOA rail is designed to tilt the scope for long range shooting. If the high rings are both the same height, they will not have the same effect.

This is correct, we are looking to build a forward slope to provide a head start (a sort of bias, as stated above) on your scope adjustments. If the rings are parallel, then the only effect of a change in height is the geometry when we go to calculate drop beyond your zero distance.

For example, the same .223 load in both a standard AR-15 and a typical bolt action do not share the same trajectory for any given zero distance. The reason is that the sight height on the average AR is about 2-1/2", while the average bolt action will be closer to 1-3/4". Because we must dial out this distance when we zero (converge the bore with the optic's line of sight), we set up a different departure angle for the bullet, about 3/4 moa or .2 mils. Because the AR has to have a steeper departure angle dialed on to get zeroed, it seems to have less drop beyond its zero distance.

Burris Signature rings have inserts that can be changed and adjusted to give a bit of angle to the scope. It would save you from needing an angled scope base.

Yes, these can provide some help if the correct inserts are used.

LOL, thanks Yoda.

LOL, I was on the fly earlier, had to get something to eat, couldn't get my forearms to rest on my belly properly.

Depends on the scope. Some have more adjustment.

This is true, in a flat shooting cartridge, coupled with a scope of generous adjustment range, a 20 moa base is not absolutely necessary, but is often desirable.

May as well use a 20moa rail as it doesn't hurt you to have it. Might not want it now but maybe later.

Exactly. Even if your rifle/scope combo doesn't command it, a sloped base keeps you in the area of best performance of your scope - near mechanical center.

For habitual long range shooters, you will be working more near the center of your scope's adjustment range with a sloped base of some sort. For example, if you shoot 600-800 yards with a .308/175 match load and everything on your rifle is straight, you install a 20 moa base and dial *down* 20 minutes to get zeroed. Now, you go to 750 yards and dial *up* approximately 20 minutes for your required elevation and bingo, you're back in the center of your scope's mechanical adjustment range. The extra benefit is that when you do go to the most distant targets, you're not bottoming out your adjustments and the chance of staying linear is better.

In other situations, you'll be pushing the limits of your scope, even with a 20 moa base.

For instance, suppose you look at scopes and settle on the Viper Vortex 6.5-20x50 PA. The specs show this scope as having 65 moa total elevation adjustment.

First off, this number is divided in two, since half is *up* travel, half is *down* travel and we only use the *up*. You are now left with a 32-1/2 moa range of *up* adjustment. Already you can't dial up enough to be dead on at 1,000 yards with a .308.

But wait, there's more...

We will next need to dial out raw drop and convergence to get a mechanical zero. If we are zeroed at 100 yards, this number is about 4-1/2 moa, assuming your rifle is straight and everything bolts up into perfect alignment - good luck.

But wait, there's more...

If you are not perfectly centered with your windage adjustment, you will lose additional elevation. You can compare the loss of headroom to walking through an arched doorway and moving off center. The further off center you go, the less headroom there is. If you have to really crank your windage turret over to get your initial zero, rest assured you are not getting your specified elevation travel.

I think that's it...

So, the specs say "65 moa", but we actually have 65 divided by 2 minus 4-1/2, about 28 moa. A 20 minute base will make that 48 moa, which gets the average .308 well past 1k.

Fellas, Fellas, just trying to get a discussion going, lol.

You've been around here long enough to know better.

With all the "tacticool" items out there, just wanted to discuss need to have, versus nice to have.

Q

There really isn't any compelling reason to have a flat base on a long range rifle and 20 moa is the default.

Go to 30 moa and some scopes will not be able to dial down far enough to zero at 100 yards. Go to a 10 moa base and a number of scopes will not dial the elevation necessary to get to 1k.

If you know your scope specs and cartridge ballistic path, you can get the most from your scope. I made a wedge shaped base so that my .22 was about 3-4 clicks above bottom at my 75 yard zero and it allows me to dial out to 350 and hold dead on, and I can get to 400 if dial it all the way up and hold a couple mils high.

 

[Qbeam]

Ed,

Thanks for the in depth explanation. I appreciate your in depth explanations, as does most of the members here. I was looking at the Vortex scopes for a 308. I will use your posts as guidance.

Thanks again,

Q

 

[Pinecone]

I am seriously considering going to a 30 MOA base.

With my Viper PST 6-24x, I have 15 mils of up available. At 1200 yards, I need 15.5 mils.

And I did the numbers, I would still be able to zero at 100 yards with a 30 MOA base.

My .22 trainer has a 25 MOA base. But that is because that is what is made for it.