How to tell you have a 20 MOA base?

Just got done reading a loooooong thread on zeroing a Vortex here on the optics board, and am now so confused that I'm afraid I may have brained my damage.

So maybe a quick question or two for you "sharp" shooters (see what I did there…?) will help me get the concept of MOA bases.

When I purchased my model 12 BVSS in 223 new, the shop owner installed a set of leupold bases and the scope I'd purchased separately.

Every scope (6 now) I've put in those rings and bases has been very near bottomed out on the elevation turret when zero'd at 100 yds.

Not so with my new 12FV. I installed new rings and bases for that rifle and it's near middle of the MOA capacity at 100 yd zero. Same with my shooting buddy who purchased the same Vortex Viper HS 6-24x50. Went to the 1000 yd range this week and he didn't have enough MOA to hit 500 yds where as I was only in the middle of my turrets capacity at 750. (He's shooting a 308)


As I'm typing this, it seems pretty clear that I do have a 20 moa base. If so, how would I tell?

They are thicker on back of receiver, than the front. Really not needed till 600 yds. Your buddies may be on backwards if shooting low, should be able to hit at 500 yds. with standard base.

Buddy's is an AR10 with mount machined into upper. Needed 27 moa UP to zero at 100. Tried switching rings around. No difference.

On a round receiver it should be pretty obvious it is pitched (as opposed to 0 MOA) just by looking at it. On (rear) flat receiver it is a little harder to see. To confirm that it is actually 20 MOA, your going to want some calipers and a calculator. I did a little quick math and it looks like 20 MOA would be .0349" rise over a 6" run. That was very quickly done though so run the numbers yourself.

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Originally Posted by Texas10

Buddy's is an AR10 with mount machined into upper. Needed 27 moa UP to zero at 100. Tried switching rings around. No difference.

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There are offset AR mounts with 20 minutes correction built it. If he is using reg rings on the picatinny rather than an offset, Burris Signature rings should do what he needs to do. They make a tactical style Signature as well as the Zee rings.

If there is difference in height with the rear of base vs front, it is probably 20MOA. Mine is noticeably different. There are also 30MOA bases too but you could just measure from the seem where base meets action to the picatiny wings. Probably the easiest way to tell without removing base...

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Originally Posted by Texas10

Just got done reading a loooooong thread on zeroing a Vortex here on the optics board, and am now so confused that I'm afraid I may have brained my damage.

So maybe a quick question or two for you "sharp" shooters (see what I did there…?) will help me get the concept of MOA bases.

When I purchased my model 12 BVSS in 223 new, the shop owner installed a set of leupold bases and the scope I'd purchased separately.

Every scope (6 now) I've put in those rings and bases has been very near bottomed out on the elevation turret when zero'd at 100 yds.

Not so with my new 12FV. I installed new rings and bases for that rifle and it's near middle of the MOA capacity at 100 yd zero. Same with my shooting buddy who purchased the same Vortex Viper HS 6-24x50. Went to the 1000 yd range this week and he didn't have enough MOA to hit 500 yds where as I was only in the middle of my turrets capacity at 750. (He's shooting a 308)


As I'm typing this, it seems pretty clear that I do have a 20 moa base. If so, how would I tell?

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simplest way is to dial your scope to its limits both up and down and compare it to your 100 yrd zero. now don't lose your 100 yrd zero doing this exercise.

Example: your scope literature says your scope has 60 moa of elevation adjustment. That should be about 30 up and 30 down with a 0 moa base. With a 20 moa base you would only have about 10 down and 50 up. Now these numbers are not cast in stone. Don't be surprised if your 60 moa scope only has 55 moa of elevation or something else. If you have a zero stop set for your 100 yard zero just check how much elevation you have up and compare that to your scopes total elevation adjustment.

easiest way for me to tell. Only takes a minute.

Ok so I lied... It's probably not noticeable to the eye. My math goes like this 1 MOA at 100 yards is 1.04"... So 1.04/3600 (3600"=100yds) is .00029"/1" elivation or .00174"/6". I don't think I can see that with my naky eye... Is my math wrong?

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Originally Posted by Russmerle

Ok so I lied... It's probably not noticeable to the eye. My math goes like this 1 MOA at 100 yards is 1.04"... So 1.04/3600 (3600"=100yds) is .00029"/1" elivation or .00174"/6". I don't think I can see that with my naky eye... Is my math wrong?

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Only in that you forgot to take your number (1 MOA) and multiply it by 20 to get .0349 for 20 MOA. Your eye can see that. 1 MOA would be tough.

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Originally Posted by rovert

Only in that you forgot to take your number (1 MOA) and multiply it by 20 to get .0349 for 20 MOA. Your eye can see that. 1 MOA would be tough.

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Thanks you're right... So it's not in my head that I can see a difference lol

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Originally Posted by Texas10

Just got done reading a loooooong thread on zeroing a Vortex here on the optics board, and am now so confused that I'm afraid I may have brained my damage.

So maybe a quick question or two for you "sharp" shooters (see what I did there…?) will help me get the concept of MOA bases.

When I purchased my model 12 BVSS in 223 new, the shop owner installed a set of leupold bases and the scope I'd purchased separately.

Every scope (6 now) I've put in those rings and bases has been very near bottomed out on the elevation turret when zero'd at 100 yds.

Not so with my new 12FV. I installed new rings and bases for that rifle and it's near middle of the MOA capacity at 100 yd zero. Same with my shooting buddy who purchased the same Vortex Viper HS 6-24x50. Went to the 1000 yd range this week and he didn't have enough MOA to hit 500 yds where as I was only in the middle of my turrets capacity at 750. (He's shooting a 308)


As I'm typing this, it seems pretty clear that I do have a 20 moa base. If so, how would I tell?

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Texas10


Do I understand that your base is in two pieces? Each attached to the receiver with two screws in front of and behind the feed/ejection port? I've not heard of two piece bases other than 0 moa= flat. You might have flat bases? And those would likely need to be shimmed or bedded to align with each other (as could account for the needed scope adjustment) as Savage receivers are known to need this. My Mdl 10 receiver is .007" higher in the front. So I had to shim the back of the 20 moa base mounted on it. BTW, you can see the 20 minutes of cant in a one piece base.


Snipe

Yes, I have Leupold 2 piece bases. Looks like this http://www.opticsplanet.com/leupold-...iece-base.html

But, I can't find any reference to a 20 moa base in this style from Leupold either. Which leaves me confused.

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Originally Posted by Texas10

Yes, I have Leupold 2 piece bases. Looks like this http://www.opticsplanet.com/leupold-...iece-base.html

But, I can't find any reference to a 20 moa base in this style from Leupold either. Which leaves me confused.

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simple way to tell. try this!

simplest way is to dial your scope to its limits both up and down and compare it to your 100 yrd zero. now don't lose your 100 yrd zero doing this exercise.

Example: your scope literature says your scope has 60 moa of elevation adjustment. That should be about 30 up and 30 down with a 0 moa base. With a 20 moa base you would only have about 10 down and 50 up. Now these numbers are not cast in stone. Don't be surprised if your 60 moa scope only has 55 moa of elevation or something else. If you have a zero stop set for your 100 yard zero just check how much elevation you have up and compare that to your scopes total elevation adjustment.

easiest way for me to tell. Only takes a minute.

Sorry, I guess I left that little detail out. The turret on this scope is 12 moa per rotation, and I am one rotation from bottom at 100 yd zero leaving me about 35 moa available up adjustment, which strikes me as an interesting number since that would work out to be something like a 11 or 12 moa base. Not exactly common.

The rings are Leupold also, 30mm. I bought these recently, and am pretty sure they're STD rings.

Interestingly, the manual included with the scope includes no technicial data whatsoever, but I seem to remember reading somewhere that the scope has 50 moa total. Here's a link. http://www.opticsplanet.com/vortex-v...RHSR-VHS-4319A

Assuming the base is a STD base, does it sound to you like the scope might be FUBARd?

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Originally Posted by Texas10

Sorry, I guess I left that little detail out. The turret on this scope is 12 moa per rotation, and I am one rotation from bottom at 100 yd zero leaving me about 35 moa available up adjustment, which strikes me as an interesting number since that would work out to be something like a 11 or 12 moa base. Not exactly common.

The rings are Leupold also, 30mm. I bought these recently, and am pretty sure they're STD rings.

Interestingly, the manual included with the scope includes no technicial data whatsoever, but I seem to remember reading somewhere that the scope has 50 moa total. Here's a link. http://www.opticsplanet.com/vortex-v...RHSR-VHS-4319A

Assuming the base is a STD base, does it sound to you like the scope might be FUBARd?

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If she is FUBAR'd I'd say she's FUBAR'd in the right direction ;)

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Originally Posted by Texas10

Sorry, I guess I left that little detail out. The turret on this scope is 12 moa per rotation, and I am one rotation from bottom at 100 yd zero leaving me about 35 moa available up adjustment, which strikes me as an interesting number since that would work out to be something like a 11 or 12 moa base. Not exactly common.

The rings are Leupold also, 30mm. I bought these recently, and am pretty sure they're STD rings.

Interestingly, the manual included with the scope includes no technicial data whatsoever, but I seem to remember reading somewhere that the scope has 50 moa total. Here's a link. http://www.opticsplanet.com/vortex-v...RHSR-VHS-4319A

Assuming the base is a STD base, does it sound to you like the scope might be FUBARd?

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I think if you do a little search you will find that most of the so called 20 MOA bases are not really 20 moa. 10 to 15 is most common.

Sounds like you got confused after reading my thread and I dont blame you. From the outside looking in its pretty clear but once you step off in it it gets cloudy as hell. The canted base is there to shift your cross hairs down in adjustment so you have more up available. If it were exact, it would take 20 from the down and put it into the up available.

When I look at my scope on my remington action (short rail), I can see the cant. When I look at the supposedly 20 moa rail on 110ba rail (long rail), it becomes nearly impossible to see because I loose the reference to the barrel under the continued rail. Since it sounds like you are just using either a two piece or, just 20 moa rings, you should be able to see a cant between the bottom of the scope and the top of the barrel. You could also just slap on a level to the barrel. Get the barrel level then check the level of the scope and it should be going down hill pretty well.

By the way, if you could have read that thread and not walked away with brain damage, it was too late for you anyway. lol

Wait a minit, wait a minit, your all wrong every one of you. Youve gotta first find which direction is north, meaning (true) north and start from there. lol

Wow. I never thought about that. Not to mention angle of the sun and it's reflective properties. You know that black is the presence of all colors lol.

I think you hit it Doc. With the loooooong sun shade on the scope, I can't see any difference in spacing between the barrel and scope, but then the barrel is tapered in exactly the direction that would make it look parallel to the scope IF the scope were canted down slightly.

And as I was setting the scope back in the rings yesterday before going to the range, I noticed that with the top halves of the rings off, when I press on the scope body over the rear ring, the front of the scope rises off the front ring slightly. So the rings are not exactly in line, another sign that I need to get a one piece rail with a 20 moa lift if I'm going to pursue ringing steel at long distances.

Quite a learning process!

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Originally Posted by Texas10

I think you hit it Doc. With the loooooong sun shade on the scope, I can't see any difference in spacing between the barrel and scope, but then the barrel is tapered in exactly the direction that would make it look parallel to the scope IF the scope were canted down slightly.

And as I was setting the scope back in the rings yesterday before going to the range, I noticed that with the top halves of the rings off, when I press on the scope body over the rear ring, the front of the scope rises off the front ring slightly. So the rings are not exactly in line, another sign that I need to get a one piece rail with a 20 moa lift if I'm going to pursue ringing steel at long distances.

Quite a learning process!

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now that is a really bad situation. Not at all good for a scope. I would not even install a scope in rings like that. If it is not too bad lapping your rings could fix it. Otherwise you need to go in a different direction.

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Originally Posted by Texas10

I think you hit it Doc. With the loooooong sun shade on the scope, I can't see any difference in spacing between the barrel and scope, but then the barrel is tapered in exactly the direction that would make it look parallel to the scope IF the scope were canted down slightly.

And as I was setting the scope back in the rings yesterday before going to the range, I noticed that with the top halves of the rings off, when I press on the scope body over the rear ring, the front of the scope rises off the front ring slightly. So the rings are not exactly in line, another sign that I need to get a one piece rail with a 20 moa lift if I'm going to pursue ringing steel at long distances.

Quite a learning process!

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dude it is quite simple. If you have considerably more up elevation adjustment then you do down adjustment from your 100 yrd zero you have canted scope bases.

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Originally Posted by m12lrs

dude it is quite simple. If you have considerably more up elevation adjustment then you do down adjustment from your 100 yrd zero you have canted scope bases.

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It's not quite that simple. In a perfect world it would be. If they are two piece bases I'm pretty certain they are not meant to be 20 MOA bases. I've never seen such a thing. It would be possible but I don't know that anyone offers them. The bases would definitely long action/short action specific and the front and back bases would have to be oriented properly.

I doubt that is the case here. I see three possibilities. One is the action is quite far out of spec. Two is the bases are out of spec or are not the correct bases. Three is the rings are out of spec. As things are described I would lean towards the bases being incorrect. Something is misaligned pretty badly if the scope lifts off the front ring when placed squarely in the rear. Take the rings off and put a straight edge on the rear base. If it floats over the front it is not the rings. Take the bases off and put the straight edge on the action. If, when held tight to the rear screw tappings, it floats at the front screw tappings it is an action problem. If the action is straight it is a base problem.

The action test assumes a round receiver. If this is a rear flat receiver I almost bet that the bases were not matched properly for the application. If you want to keep the 20 MOA two piece system that you have stumbled on to I would suggest Burris Signature rings. They should allow the scope to be secured without applying unwanted torque to the tube. You may be able to lap the rings to accomplish the same but it sounds like a lot.

Best solution: get a real 20 MOA one piece base. (If the action is ok)

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Originally Posted by rovert

It's not quite that simple. In a perfect world it would be. If they are two piece bases I'm pretty certain they are not meant to be 20 MOA bases. I've never seen such a thing. It would be possible but I don't know that anyone offers them. The bases would definitely long action/short action specific and the front and back bases would have to be oriented properly.

I doubt that is the case here. I see three possibilities. One is the action is quite far out of spec. Two is the bases are out of spec or are not the correct bases. Three is the rings are out of spec. As things are described I would lean towards the bases being incorrect. Something is misaligned pretty badly if the scope lifts off the front ring when placed squarely in the rear. Take the rings off and put a straight edge on the rear base. If it floats over the front it is not the rings. Take the bases off and put the straight edge on the action. If, when held tight to the rear screw tappings, it floats at the front screw tappings it is an action problem. If the action is straight it is a base problem.

The action test assumes a round receiver. If this is a rear flat receiver I almost bet that the bases were not matched properly for the application. If you want to keep the 20 MOA two piece system that you have stumbled on to I would suggest Burris Signature rings. They should allow the scope to be secured without applying unwanted torque to the tube. You may be able to lap the rings to accomplish the same but it sounds like a lot.

Best solution: get a real 20 MOA one piece base. (If the action is ok)

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you missed my post above. I would not even install my scope in rings like that. You could damage the scope.

the post you referenced was just to tell if you had a canted installation.

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Originally Posted by doctnj

Wow. I never thought about that. Not to mention angle of the sun and it's reflective properties. You know that black is the presence of all colors lol.

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I actually didnt know that, but it might help explain a few other things i dont understand either.

As for the 2 pc Leupold base, theres not a thing wrong with using them.
If your having issues with elevation, try removing just the rear section and
installing a few thickness of your favorite beverage can as shims. See if that helps
with the zero issue. At least you will have done something that wont hurt or cost anything.
There was a time in the not very long ago past that tapered piccitiny bases werent available.
And the only way to deal with getting max elevation was to have the base milled or install shims.
I might still have some shims under a Redfield base on one of my guns.

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Originally Posted by rovert

It's not quite that simple. In a perfect world it would be. If they are two piece bases I'm pretty certain they are not meant to be 20 MOA bases. I've never seen such a thing. It would be possible but I don't know that anyone offers them. The bases would definitely long action/short action specific and the front and back bases would have to be oriented properly.

I doubt that is the case here. I see three possibilities. One is the action is quite far out of spec. Two is the bases are out of spec or are not the correct bases. Three is the rings are out of spec. As things are described I would lean towards the bases being incorrect. Something is misaligned pretty badly if the scope lifts off the front ring when placed squarely in the rear. Take the rings off and put a straight edge on the rear base. If it floats over the front it is not the rings. Take the bases off and put the straight edge on the action. If, when held tight to the rear screw tappings, it floats at the front screw tappings it is an action problem. If the action is straight it is a base problem.

The action test assumes a round receiver. If this is a rear flat receiver I almost bet that the bases were not matched properly for the application. If you want to keep the 20 MOA two piece system that you have stumbled on to I would suggest Burris Signature rings. They should allow the scope to be secured without applying unwanted torque to the tube. You may be able to lap the rings to accomplish the same but it sounds like a lot.

Best solution: get a real 20 MOA one piece base. (If the action is ok)

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Winner winner chicken dinner. Best answer by far.
My guess would be that the action is out of spec. I've run into that before.
To continue using the same bases, shim under the low one as yobuck suggested. Except use shims made for the job: http://www.midwayusa.com/product/154...-package-of-10
Or switch to a one-piece rail. Which should be shimmed as well, to get proper contact, or bedded, or neither if you're in a hurry.

Thanks for all the responses, guys. Really learned a lot about scopes, bases , rings and alignment, and appreciate you sharing your experiences and wisdom.

The scope on my Savage shoots great, despite the irregularities. Got plenty of up adjustment for 750 yard shooting, and may even go for 1000 some day, but apparently it is all an accident. Nevertheless, it works. I will continue to plan on getting a 20 moa one piece base and some better rings soon, if for no other reason than to have a reliable set up that i can move to another gun if necessary.

Thanks again.

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Originally Posted by rovert

It's not quite that simple. In a perfect world it would be. If they are two piece bases I'm pretty certain they are not meant to be 20 MOA bases. I've never seen such a thing. It would be possible but I don't know that anyone offers them. The bases would definitely long action/short action specific and the front and back bases would have to be oriented properly.

I doubt that is the case here. I see three possibilities. One is the action is quite far out of spec. Two is the bases are out of spec or are not the correct bases. Three is the rings are out of spec. As things are described I would lean towards the bases being incorrect. Something is misaligned pretty badly if the scope lifts off the front ring when placed squarely in the rear. Take the rings off and put a straight edge on the rear base. If it floats over the front it is not the rings. Take the bases off and put the straight edge on the action. If, when held tight to the rear screw tappings, it floats at the front screw tappings it is an action problem. If the action is straight it is a base problem.

The action test assumes a round receiver. If this is a rear flat receiver I almost bet that the bases were not matched properly for the application. If you want to keep the 20 MOA two piece system that you have stumbled on to I would suggest Burris Signature rings. They should allow the scope to be secured without applying unwanted torque to the tube. You may be able to lap the rings to accomplish the same but it sounds like a lot.

Best solution: get a real 20 MOA one piece base. (If the action is ok)

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Now you have seen it
https://www.midwayusa.com/product/59...ear-axis-matte

^ that product has been discontinued by Midway. ^

The same 20 MOA 2 piece bases cannot work on both a long and short action. That Geometry does not work. Maybe Midway should have listed an option for both the long and short actions. Or maybe they didn't sell because of the $86 price tag, which is ridiculous, even for Night Force.

But I think the mix up on this product listing is with Midway, not Night Force ?

"T 10" you now know all you could ever know about a problem you don't have! :-) As you said, your rifle shoots well. But if you still want to perfect away the issues you may have, you've answered those questions also. Go with a one piece base, or the Burris Zee rings. :-) The Brotherhood always comes through! :-)

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Originally Posted by Russmerle

If she is FUBAR'd I'd say she's FUBAR'd in the right direction ;)

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+1 on that



Snipe

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Originally Posted by Texas10

Thanks for all the responses, guys. Really learned a lot about scopes, bases , rings and alignment, and appreciate you sharing your experiences and wisdom.

The scope on my Savage shoots great, despite the irregularities. Got plenty of up adjustment for 750 yard shooting, and may even go for 1000 some day, but apparently it is all an accident. Nevertheless, it works. I will continue to plan on getting a 20 moa one piece base and some better rings soon, if for no other reason than to have a reliable set up that i can move to another gun if necessary.

Thanks again.

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Never meant to imply that it's an "accident". It simply is what it is. Sounds like the only problem that you have with your setup, is that your bases are not on the same plane with each other, which is hard on your scope tube when tightened down. I would suggest trying to correct that situation before installing any scope that you value very highly, because it may well cause damage. There are several routes to do this, many have already been mentioned. Just be aware that fixing this problem may actually cause you to have less elevation available than you do now. Up to you to decide if you want to leave it as-is or try to level out your rings.
The Burris rings with inserts mentioned above are another good option if you decide to mess with it.