Rifle Scopes Do I want / need a 20 MOA base?

H

holdem

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Minuteman
Nov 4, 2009
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Orlando, FL
#1
I have a Sig SSG 3000. I am getting close to a NightForce scope, either the 8-32 or 12-42 benchrest model.

Do I want / need a 20 MOA base for this set up?

95%+ of the shooting will be done a 300 meter F-Class. Some will be done at 100 yards (playing, zeroing). And I hope to try out a 600 yard F-Class match. I would like to shoot beyond that some day, but chances will be limited, and who knows if it will ever happen.

Will a 20 MOA base still work at 100 yards? Have far out can I push this set up on a 0 MOA base?
 
#3
Re: Do I want / need a 20 MOA base?

<span style="font-style: italic">"Give a man a fish, and you feed him for a day. Teach a man to fish, and you feed him for life."</span>

So, I could give you the answer, but I'd rather teach you to fish.

Steps:

1) Go here: Nightforce BenchRest Models

2) Note the internal adjustment range for both scopes.

3) Once you have the vertical adjustment range, divide it by 2, to account for the fact that half of the range is up and half is down.

4) Take off additional 5 moa to account for zeroing.

5) Subtract 20 moa from the remainder. If the answer is a negative number, then a 20 moa base will NOT allow you to get a 100 yd zero. You might need a 15 moa or 10 moa base.

6) To compute how far out you can push a 0 moa base, go here, and follow the instructions:

JBM Ballistics

See that was easy.....
 
#6
Re: Do I want / need a 20 MOA base?

The price of a 20 MOA base vs a flat base is minimal. Why not have it and not need it? There might be that one day that you decide to go a little further and your scope might not have the adjustment you need to get out there. This is where the 20 MOA base will come in.
 
#7
Re: Do I want / need a 20 MOA base?

BobinNC - Thanks a bunch. If I understand correctly, then a 20 MOA will not allow me to zero at 100 yards with that scope. Also if I understand correctly, I can push the 0 MOA base and 12-42 out to 600 yards. Beyond that, I would need a different base.

I should also add that I already have the 0 MOA base, it came on the gun. Getting a 20 MOA would be an extra expense.

And a follow up question, why only 40 MOA of travel on the 12-42 and 50 MOA on the 8-32. Would I be better off giving up some of the magnification and gaining the 10 MOA of travel?
 
#8
Re: Do I want / need a 20 MOA base?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: holdem</div><div class="ubbcode-body">BobinNC - Thanks a bunch. If I understand correctly, then a 20 MOA will not allow me to zero at 100 yards with that scope. Also if I understand correctly, I can push the 0 MOA base and 12-42 out to 600 yards. Beyond that, I would need a different base.

I should also add that I already have the 0 MOA base, it came on the gun. Getting a 20 MOA would be an extra expense.

And a follow up question, why only 40 MOA of travel on the 12-42 and 50 MOA on the 8-32. Would I be better off giving up some of the magnification and gaining the 10 MOA of travel? </div></div>

Holdem,

The why's of why the NFBR 12-42 has only 40 MOA of travel has to do with the optic design of high X scope which I'm not qualified to comment on. I know nothing about F class and the optimum magnification required to be competitive.

Actually with the 8-32 you could pick up more than 10 MOA, if you are willing to change to a canted base.

For example: 8-32 has 50 MOA of travel, that's 25 moa up and 25 down. Add say a 20 MOA base, and you now theoretically have 45 MOA up and 5 MOA down.

In optics you usually have to give up something to get something. In your case you have to give up some X power to get more elevation travel. I cannot say whether the trade is worth it.

Bob
 
#9
Re: Do I want / need a 20 MOA base?

Bob,
Just trying to understand, but maybe I'm missing something here. Do the NF benchrest models have the elevation adjustment "centered" within the travel range from the factory? I have several of the NXS models, including 3.5-15x50 in F1 and F2, and a 5.5-22x50. These are currently mounted on weapons that have either no cant at all, or a 20 MOA cant mount. None of the three has required more than a few mil upward elevation (at most) to zero at 100 yd (the elevation turrets are set at the extreme <span style="font-style: italic">low</span> end from the factory). So, I'm not really understanding your reference to "half the total elevation travel up and half down". Unless the benchrest models are set in the center of the elevation travel from the factory, in practice "half up and half down" is not correct as most of the upward elevation travel is still available after zero at 100 yd, even with a 20 MOA base.

At 1000 yd, an SMK 175 at 2600 fps will require in the neighborhood of 11.3 mil (38.7 MOA) elevation according to JBM. Depending on how much elevation was required to zero one of the BR models, it seems like it should be close to having enough elevation to reach 1000 yd (50 MOA total - elevation to 100 yd zero), even with a flat base. With a 20 MOA base, it should be no problem at all. So am I missing something?
 
#10
Re: Do I want / need a 20 MOA base?

gataylorg,

Most scopes tactical, benchrest or other are shipped optically centered. So 50 MOA usually means 50 MOA total of elevation adjustment; thus 25 moa up and 25 moa down. So if the OP needs 38 MOA to reach 1kyds, a 50 MOA elevation scope will not get him there, unless he uses a canted base, because he has only 25 MOA of UP available.

Putting it another way, if scopes were NOT optically centered, and were in fact centered in the lower half or 3/4's of their available adjustment range, then there would be NO reason to ever use a canted base.

A canted base does not add MOA. It just takes MOA from the down adjustment, and adds it to the up adjustment. So a 50 MOA elevation adjustable scope (centered with 25 MOA up and 25 MOA down) adding a 20 MOA base would yield theoretically 45 MOA up and 5 MOA.

Of course there are exceptions, just off hand: Premier Heritage scopes, and USO's with EREK knobs. These designs allow (after setting) optimized use of most of the available UP reticle travel. I'm sure there are others, but NF BR models are not among them.

So yes, you are missing something: How scopes are designed...
 
#11
Re: Do I want / need a 20 MOA base?

Bob,
Thanks for your reply. I made a couple inquiries and now I understand a lot better why I was under the mistaken impression that my NFs came with the elevation adjustment near the lower end. As you pointed out, I was wrong and this is not the case. From the discussions, the probable reason I was led to incorrectly believe this to be the case has to do with the visual appearance of the turrets and the zero stop feature on all the NF scopes I own. I understand now that were I to determine how much upper elevation travel remained in any of my rifles/scopes at 100 yd zero, it would in fact be less than half of what I previously thought it to be. Sorry if my comment/question created any confusion, and thanks for prompting me to learn a little more about the topic.
 
#12
Re: Do I want / need a 20 MOA base?

This thread has been good for me. I think I am going to stay with the 0 MOA base. I already have it, so there is no extra expense. I can always buy the 20 MOA base later (if needed) and re-zero.

I think I am going to stay with the 12-42. While the 8-32 would work fine, I like having the extra magnification.

However, it has made me reconsider the reticle. I had thought of a target reticle, very fine hash marks solely for F-Class type shooting. But I now think I will get a hash mark mil reticle. This will allow me to hold over if I ever need it.
 
#13
Re: Do I want / need a 20 MOA base?

holdem:

You should get the Burris Signature Zee rings. They come with offset inserts that obviate the need for a canted base.

You could use the offset inserts to add effective cant to your scope mount if you find you need it.

In my case, I had an F-class gun with a 20moa base but could not, as BobinNC intimated, zero my NF BR 12-42 at 100 yards with the centered inserts (I also like the rings high and apparently that has an effect). I used the offset inserts to make the total cant something less than 20moa (couldn't be bothered to figure it out but the instructions include the formula), and now the rifle is zero'ed at 100 yards and I can click all the way up to 1000.
 
#14
Re: Do I want / need a 20 MOA base?

OK them I must be doing it all wrong and have been for years. All my rifles are zeroed at 100 yds. I have a full 80 MOA's of up about 6 of down. I can't think of a time you need to dial down below your 100 yd. zero because at 50 yds. you to come up at least 3 to 4 inches depending on the round you are shooting. So with this being the case at least with my rifles why would I want to waste 40 MOA's to get a zero I have 20 MOA bases on all my stuff. Maybe I just can't understand how that works.
 
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