Rifle Scopes 30 MOA or 40 MOA?

C

Cold_Bore_88

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Jul 13, 2013
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The Woodlands, TX
#1
I have a .338 LM being built by SAC. The action is an Alpha 11 (Defiance) with a 20 MOA integral base. I want to get this rifle out to a mile (1610m). According to AB, this will take 21.5 mrad. I am using an S&B 5-25x56 PMII with 26 mrad.

Ideally, I think I will need a 10 MOA rail (approx 9 mrad total with 20 MOA base) to easily get to a mile. These leave me with roughly 4 mrad to play with. The problem here is that I will need to special order the Spuhr SP-4301 (who knows how long that will take).

The other option is to get another 20 MOA in a unimount (total of approx 12 mrad with bade). However, I fear I won’t be able to zero at 100 and I will be at the bottom of my turret with the least glass clarity.

Give me your opinion. Go with the special order 10 MOA base or just get a 20 MOA?




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#4
Don't laugh but these will actually work and a bunch cheaper than custom 10 MOA Spuhr mount....https://www.burrisoptics.com/mounting-systems/rings/xtr-signature-rings

Each ring set includes one set of the +/- 0 MOA concentric, one set each of the +/-5 MOA and +/-10 MOA, and two sets of the +/-20 MOA. With these inserts, it is possible to make 0, 5, 10, 15, 20, 25, 30 or 40 MOA of cant in the scope mount.
 
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#6
lash said:
Do the math. 40 MOA total is less than 12 Mils. You will be fine with the 20 MOA mount and a S&B.
Click to expand...

Thanks! In my S&B, do I assume that all 26 mrad are up? So when I get the scope mounted, it will already be set towards the bottom of its elevation?

I apologize for the potentially dumb question but I always thought the scopes came centered in Vertical and horizontal windage (13 mrad up and 13 mrad down).


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#7
The Schmidt & Bender 5-25x56 scope is designed to use a 45 moa base and still be able to zero @ 100m. You will be fine with a Spuhr 20.6 moa mount (plus your 20 moa base on your Defiance action).
I use a Spuhr SP-4602 with a S&B 5-25x56 on a 338 LM Defiance Deviant action in a AIAX chassis and it works fine.
 
#10
You are really over thinking this. Don't worry about your max dialing range, but look at the other end. Try to get as much as cant as you can while still being able to zero the rifle. If you can zero at 100 without bottoming out, you don't have too much.
 
#12
You’ll be fine with the 20 moa integral mount. You can also go with a 20 moa scope mount for 40 moa total. The S&B has plenty of internal travel to accommodate either. Personally, I would just put a pair of rings on the integral base and be done with it.

Also, don’t worry about Amsdorf. He was asking for help mounting a scope on his 338 a few months ago. He’s also a pastor, but won’t hesitate to call you every name in the book via pm. I’ll probably get another slew of them after he reads this. Hahahaha. A real knowledgeable asset to the shooting community.
 
#13
If you have a 20 MOA rail built in, I don't believe you'd "need" any more offset. Even if you only had 10 of the 26 available mils left after zeroing at 100, you'd only need 8.9 mils of adjustment based off of a MV of 2900 and G1 BC of .670 (Hornady 285 gr. 338 LM data, and unknown barrel length in this assumption). You'll likely be able to use at least 16 mils with the built in 20 MOA(5.925 mils) rail and that is plenty for 1760 yards. I don't know how optical performance is on the S&B at that range of elevation, but the S&B's I've had a chance to look through had no issues resolving an image.
 
#14
Cold_bore_88,

Agreed with the above statement you will have enough with your 20 moa base. The 26 mil travel with the S&B is 13 up 13 down. It should come centered. So, converting mil to moa and you have a total of 48.5 MOA up in travel alone. I'm assuming you are getting a mil reticle in which you'll normally have 38 more moa hold. A general sea level calculation says you'll need 72 moa to get to one mile with a .300 gr. Nos CC. I used that bullet as it doesn't have the highest BC. So, it gives some leeway in what you need. In any case you've got what you need, but would have to use hold as well as dialing up

If you were to reduce in power in your scope choice, you will find you can get more travel out of it. With glass as clear as S&B, you might consider this. We've shot many times to a mile on a man sized silhouette steel, either with a 10x or a dialed down 15X scope.

Added: You can get more elevation on the base if you wanted. But, you must also remember you're not going to be shooting out to a mile all the time. Having to re-work your base system so you can shoot at 400-500 is going to cost extra rounds to rezero before you can begin. At the cost of .338 Lapua, I'd learn to use hold for the really long shots.


Amsdorf said:
If you have to ask questions like this, you are probably not ready to attempt shooting out to mile. Just sayin' ... cheers.
Click to expand...

Really??!?!? This site is to help people improve. Telling them they shouldn't do something based on asking a question isn't helping anyone improve. You just send all your nasty responses to dirthead1 because he said he's ready to hear them...:cool:
 
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#15
sandwarrior said:
Cold_bore_88,

Agreed with the above statement you will have enough with your 20 moa base. The 26 mil travel with the S&B is 13 up 13 down. It should come centered. So, converting mil to moa and you have a total of 48.5 MOA up in travel alone. I'm assuming you are getting a mil reticle in which you'll normally have 38 more moa hold. A general sea level calculation says you'll need 72 moa to get to one mile with a .300 gr. Nos CC. I used that bullet as it doesn't have the highest BC. So, it gives some leeway in what you need. In any case you've got what you need, but would have to use hold as well as dialing up

If you were to reduce in power in your scope choice, you will find you can get more travel out of it. With glass as clear as S&B, you might consider this. We've shot many times to a mile on a man sized silhouette steel, either with a 10x or a dialed down 15X scope.

Added: You can get more elevation on the base if you wanted. But, you must also remember you're not going to be shooting out to a mile all the time. Having to re-work your base system so you can shoot at 400-500 is going to cost extra rounds to rezero before you can begin. At the cost of .338 Lapua, I'd learn to use hold for the really long shots.




Really??!?!? This site is to help people improve. Telling them they shouldn't do something based on asking a question isn't helping anyone improve. You just send all your nasty responses to dirthead1 because he said he's ready to hear them...:cool:
Click to expand...

Thanks Sand, Tunnah and dirt! I appreciate the help here. You all had valid input and I think I will just stick with the 20 MOA in the action base. To be honest, I will very rarely have the opportunity to shoot that far. Just want the “ability” to do it.

Thanks for the support!


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#16
Cold_Bore_88 said:
Thanks Sand, Tunnah and dirt! I appreciate the help here. You all had valid input and I think I will just stick with the 20 MOA in the action base. To be honest, I will very rarely have the opportunity to shoot that far. Just want the “ability” to do it.

Thanks for the support!


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Click to expand...

No problem. Let us know how it works out. As a side note, my PMii 5-25 is mounted on a 30 moa rail. The scope actually has more than 26 mils of internal travel. 26 mils is the limit of what you can dial with a DT knob, so depending on the cant of your rail, you can get a 100 yd zero and still have the full two rotations of the elevation turret (26 mils). I've also read that S&B offsets the reticle in some way, to allow for more UP and less DOWN in it's centered position (I read it on the internet, so it must be true!). You could call the S&B service center in VA and talk to Jerry to get more info on that. Anyway, with 20 moa rail, I bet you will get very close to the full 26 mils from your turret, which would get you way past a mile.
 
#17
dirthead1 said:
No problem. Let us know how it works out. As a side note, my PMii 5-25 is mounted on a 30 moa rail. The scope actually has more than 26 mils of internal travel. 26 mils is the limit of what you can dial with a DT knob, so depending on the cant of your rail, you can get a 100 yd zero and still have the full two rotations of the elevation turret (26 mils). I've also read that S&B offsets the reticle in some way, to allow for more UP and less DOWN in it's centered position (I read it on the internet, so it must be true!). You could call the S&B service center in VA and talk to Jerry to get more info on that. Anyway, with 20 moa rail, I bet you will get very close to the full 26 mils from your turret, which would get you way past a mile.
Click to expand...

That’s a great idea. I actually have one of my PMIIs with them right now for a full service and reticle swap (Going to Gen II XR). I will get Jerry to give me his input too.


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#19
I'm in the same quandary with a new AR-10 in .308. The scope I'm looking at has 72 MOA vertical travel. Assuming (big assumption) the scope is zeroed midway of the vertical travel on a 0 MOA base, you immediately lose half your vertical adjustment.

Using the same ballistic info as my .30-06, the difference between 20 & 30 MOA bases gets me from 1,500 to 1,600 yards. Barrett has a base/rings combo that is adjustable at either 15 or 40 MOA and another that is either 20 or 30, but I am going to check out those Burris XTR Signature Rings many thanks to BobinNC. The nature of these might also mitigate the advantage of the one piece integral base/ring.

That's why we ask questions like this on the forum, so we don't have to reinvent the wheel if someone else has already walked that path.

Cold_bore_88, I hope you enjoy your .338 LM. My brother just picked up an FN Ballista and we took it out the other weekend. Best group of the day was about 3/4 MOA with the flyer. If we take that one shot out of the picture it is sub 1/2 MOA. It definitely has the potential to inquire how much of an inclined base might be beyond the point of diminishing returns.
 
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#20
If I can shoot my 6.5 SLR pushing a 140 HVLD @ 2850fps out to a mile with a Kahles K624i on a 20MOA base w. 20.8MIL (dialed 17.8, hold 3) your .338LM will be fine.
I was just shooting 1771 with my .300RUM pushing a 230 Hybrid @ 3065 with a Premier Heritage 5-25×56 on a 20MOA base as well. Only took 15MIL of elevation.
 
#21
sandwarrior said:
Cold_bore_88,

Agreed with the above statement you will have enough with your 20 moa base. The 26 mil travel with the S&B is 13 up 13 down. It should come centered. So, converting mil to moa and you have a total of 48.5 MOA up in travel alone. I'm assuming you are getting a mil reticle in which you'll normally have 38 more moa hold. A general sea level calculation says you'll need 72 moa to get to one mile with a .300 gr. Nos CC. I used that bullet as it doesn't have the highest BC. So, it gives some leeway in what you need. In any case you've got what you need, but would have to use hold as well as dialing up

If you were to reduce in power in your scope choice, you will find you can get more travel out of it. With glass as clear as S&B, you might consider this. We've shot many times to a mile on a man sized silhouette steel, either with a 10x or a dialed down 15X scope.


Added: You can get more elevation on the base if you wanted. But, you must also remember you're not going to be shooting out to a mile all the time. Having to re-work your base system so you can shoot at 400-500 is going to cost extra rounds to rezero before you can begin. At the cost of .338 Lapua, I'd learn to use hold for the really long shots.




Really??!?!? This site is to help people improve. Telling them they shouldn't do something based on asking a question isn't helping anyone improve. You just send all your nasty responses to dirthead1 because he said he's ready to hear them...:cool:
Click to expand...

I learned so much in this one post. This ole brain has always been an MOA thinker and find it difficult to think in MIL and be able to picture it in my mind. I can see an MOA path but not a MIL yet. Old hunter trying new tricks (long range shooting)
 
#22
NvTwist said:
I learned so much in this one post. This ole brain has always been an MOA thinker and find it difficult to think in MIL and be able to picture it in my mind. I can see an MOA path but not a MIL yet. Old hunter trying new tricks (long range shooting)
Click to expand...

I still don't "think" in mil like I "think" in moa. Or, more true to my situation IPHY. I have to get to a calculator to make a faster conversion.
 
#23
Sandwarrior - no disrespect meant (I've been a lurker here from way back), just wanting to correct a common misconception about S&B PM II scopes. Actually, unlike most scopes, the S&B 5-25 PM II does not come with the reticle (elevation) centered.

From the factory S&B manual: "At the Schmidt & Bender factory the reticles of PM II scopes are adjusted out of center by half the amount of the full elevation range. This value must be compensated in the mount system. Forward angled mounts or rails for every Schmidt & Bender PM II scope type are available from all renowned mount manufacturers".

Thus, in the case of the PM II with a 26 MRAD DT (or MTC) knob, they are designed for the use of a 45 MOA base to offset this (26 MRAD / 2 = 13 MRAD = ~45 MOA).

Sandwarrior is correct in that you can use a 20 MOA base/mount but you might not have all of the 26 MRAD of elevation available (depending on cartridge/distance you probably won't need it).

With a 20 MOA base and a 0 MOA Spuhr mount, I had only 23 MRAD of elevation available on the elevation knob of a S&B 5-25 PM II after a 100 yd zero (300 WM), with a 20.6 MOA Spuhr mount I get the full 26 MRAD of elevation - still with a 100 yd zero).

The S&B 5-25 has over 100 MOA of internal adjustment but only 26 +/- MRAD (~89 MOA) on the elevation knob so even after a 100 yd zero, you still have room to change the zero lower (i.e. you are not bottoming out the elevation).

I know that I'm a NOOB here, but there is a lot of past discussion on this on the hide (search for lowlight's, ROB01's or Jerry's (from S&B) comments on this topic).
 
#24
carlm338 said:
Sandwarrior - no disrespect meant (I've been a lurker here from way back), just wanting to correct a common misconception about S&B PM II scopes. Actually, unlike most scopes, the S&B 5-25 PM II does not come with the reticle (elevation) centered.

From the factory S&B manual: "At the Schmidt & Bender factory the reticles of PM II scopes are adjusted out of center by half the amount of the full elevation range. This value must be compensated in the mount system. Forward angled mounts or rails for every Schmidt & Bender PM II scope type are available from all renowned mount manufacturers".

Thus, in the case of the PM II with a 26 MRAD DT (or MTC) knob, they are designed for the use of a 45 MOA base to offset this (26 MRAD / 2 = 13 MRAD = ~45 MOA).

Sandwarrior is correct in that you can use a 20 MOA base/mount but you might not have all of the 26 MRAD of elevation available (depending on cartridge/distance you probably won't need it).

With a 20 MOA base and a 0 MOA Spuhr mount, I had only 23 MRAD of elevation available on the elevation knob of a S&B 5-25 PM II after a 100 yd zero (300 WM), with a 20.6 MOA Spuhr mount I get the full 26 MRAD of elevation - still with a 100 yd zero).

The S&B 5-25 has over 100 MOA of internal adjustment but only 26 +/- MRAD (~89 MOA) on the elevation knob so even after a 100 yd zero, you still have room to change the zero lower (i.e. you are not bottoming out the elevation).

I know that I'm a NOOB here, but there is a lot of past discussion on this on the hide (search for lowlight's, ROB01's or Jerry's (from S&B) comments on this topic).
Click to expand...

Great info here! I guess I️ could have read the manual too. Hahahaha!

Ended up getting the 3 mil cant from Spuhr. The only down side is about a 30 day wait time.


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#25
carlm338 said:
Sandwarrior - no disrespect meant (I've been a lurker here from way back), just wanting to correct a common misconception about S&B PM II scopes. Actually, unlike most scopes, the S&B 5-25 PM II does not come with the reticle (elevation) centered.

From the factory S&B manual: "At the Schmidt & Bender factory the reticles of PM II scopes are adjusted out of center by half the amount of the full elevation range. This value must be compensated in the mount system. Forward angled mounts or rails for every Schmidt & Bender PM II scope type are available from all renowned mount manufacturers".

Thus, in the case of the PM II with a 26 MRAD DT (or MTC) knob, they are designed for the use of a 45 MOA base to offset this (26 MRAD / 2 = 13 MRAD = ~45 MOA).

Sandwarrior is correct in that you can use a 20 MOA base/mount but you might not have all of the 26 MRAD of elevation available (depending on cartridge/distance you probably won't need it).

With a 20 MOA base and a 0 MOA Spuhr mount, I had only 23 MRAD of elevation available on the elevation knob of a S&B 5-25 PM II after a 100 yd zero (300 WM), with a 20.6 MOA Spuhr mount I get the full 26 MRAD of elevation - still with a 100 yd zero).

The S&B 5-25 has over 100 MOA of internal adjustment but only 26 +/- MRAD (~89 MOA) on the elevation knob so even after a 100 yd zero, you still have room to change the zero lower (i.e. you are not bottoming out the elevation).

I know that I'm a NOOB here, but there is a lot of past discussion on this on the hide (search for lowlight's, ROB01's or Jerry's (from S&B) comments on this topic).
Click to expand...

Okay, I'm confused here. Is the scope "adjusted" or is the travel total set so that the reticle is "bottomed out" when you get it and the only direction you can adjust is up?
 
#26
I just picked up a Sig Tango4 6-24x50 MOA for the newest acquisition. I had been looking at the Barrett 15/40 MOA EXRings but I called Sig Optics (after I bought the scope - duh) and they told me that on a 0 MOA base perfectly aligned with the barrel, it should zero about midpoint of the full 52 MOA vertical travel. That leaves only 26 MOA or actual usable elevation adjustment, which would barely get me to 900 yards on a 300 yard zero.

A 40 MOA base would require a 675 zero with 14 MOA hold under at 100 yards! Even a 30 MOA base would require a 300 yard zero and up to 8 MOA hold under at ranges I would expect to see deer. The difference between 20 and 40 MOA bases gets me from 1,175 to 1,350 yards clicking in the entire solution, or from 1,275 to 1,450 using all the 10 MOA stadia on the reticle.

I calculated that the difference between the front and rear ring height is less than the width of a human hair for each MOA. I found out with my M1A Scout Squad that the base doesn't necessarily align true with the barrel. I'm all the way at the bottom of vertical travel and I'm still 3 inches high at 100, which would put me about dead on at 300, the range I would zero at if I had a longer range when I zeroed it.

Bottom line is, I wouldn't get much more performance with over 20 MOA in the base and if I did, it would be beyond the ranges I would be shooting. I could also end up introducing a lot of problems. I ended up going with a Warne 20 MOA mount.

It might be worth your while to boresight the scope in a 0 MOA mount/rings to see how much vertical travel you really have before you decide on a mount/ring combo. It isn't just the offset provided by the scope manufacturer, it is also how true your base aligns with the barrel.​
 
#27
sandwarrior said:
Okay, I'm confused here. Is the scope "adjusted" or is the travel total set so that the reticle is "bottomed out" when you get it and the only direction you can adjust is up?
Click to expand...

Sandwarrior, I just talked to Jerry and he said that they typically come centered (that would be @ the 13 Mil mark on the turret). I have been having Mile High mount the scope (they built my rifles) so I believe that they spun them down. So, I apologize, you are correct. Jerry said that the 5-25 mil scopes have ~30 mils of internal travel.
 
#28
carlm338 said:
Sandwarrior, I just talked to Jerry and he said that they typically come centered (that would be @ the 13 Mil mark on the turret). I have been having Mile High mount the scope (they built my rifles) so I believe that they spun them down. So, I apologize, you are correct. Jerry said that the 5-25 mil scopes have ~30 mils of internal travel.
Click to expand...

It did seem kind of odd to me, but I got to thinking as long as you knew where you were at, you could work from that point. There would be instructions on how to get it done.
 
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