0 MOA vs. 20 MOA Mount for a ZC420

[AuNEagle]

I need some rifle/scope setup advice. I’ve read some similar threads and have a feel for the recommendations given in those instances. However, the threads I found seemed more like rule of thumb types of information rather than mathematical examples. I know it will help me, and perhaps others, to work through a more detailed example.

I have a Wilson Combat 300 HAM’R on order. (I know that there are varying opinions on this new cartridge. However, it interests me and the rifle can be easily converted to a .223 with a simple barrel change.) I also have a ZCO ZC420 on order to mount on this rifle. (As a long-time photography buff, I love good glass.) When I ordered the ZC420, I also ordered a Spuhr 0 MOA mount. But now I am having second thoughts as to whether I’d be better served with a 20 MOA mount.

This rifle is going to be setup primarily as a hunting rifle. I anticipate that the vast majority of my shooting will be done within 400 yards. However, our local gun club has ranges out to 600 yards, so I may want to shoot steel at that distance occasionally. Although there are higher velocity, flatter shooting options available, I will initially be zeroing the scope for 130 gr. Speer HAM’R HOT-CORE rounds (2510 fps, 18” barrel). I’ve used both JBM Ballistics Trajectory-Drift calculator and Swarovski’s Ballistic phone app and gotten similar bullet drop results for this round.

From what I’ve read here, the recommended starting point is 1/2 the elevation adjustment range of the scope which in the case of the ZC420 is 35 mil / 2 =17.5 mil. According to my calculations, 17.5 mil is equivalent to (rounded to the nearest inch):

378” @ 600 yards
441” @ 700 yards
504” @ 800 yards
567” @ 900 yards
630” @ 1000 yards

The bullet drop calculations from the JBM Ballistics Trajectory-Drift calculator:

0” @ 100 yards
-6” @ 200 yards
-22” @ 300 yards
-53” @ 400 yards
-103” @ 500 yards
-180” @ 600 yards
-291” @ 700 yards
-440” @ 800 yards
-635” @ 900 yards
-880” @ 1000 yards

Based upon this information, it looks like I could dial out to 800 yards with the 0 MOA mount. However, it bothers me a bit to think that I am essentially giving away 1/2 of the elevation adjustment range (if I understand this situation correctly). I also get the idea that it’s better optically to operate in the middle of the adjustment range. Again, if I understand this correctly, with a 0 MOA mount I’d be starting out in the middle of the adjustment range at 100 yards and constantly moving away from that sweet spot as the distance increases.

All of the above leads me to believe I should consider switching to a 20 MOA base. However, I’m less clear on how a 20 MOA base would affect my ability to zero the scope at 100 yards. If I have to dial the scope 20 MOA from center to account for the base, 20 MOA = 5.82 mil (mrad). Since the ZC420 would give me 17.5 mil adjustment from center that I wasn’t using before, it seems I shouldn’t have a problem zeroing at 100 yards. with over 10 mil to spare).

Please check my numbers and make any corrections as necessary. I’d also be interested in your recommendations concerning a 0 MOA vs. a 20 MOA mount in my case. Thanks for your help.

 

[SepticDeath]

Get a 30 moa. You will still get your 100 yard zero and gain even more elevation than a 20 moa will. Starting out with a ZCO huh? Not messing around.

 

[BikePilot]

I'd do a 20 or 30moa mount for sure. The ZCO glass is really good, I doubt you will notice a difference as you turn the elevation turret. I can't see a difference in my 527. So you might as well get a little more elevation. I have no experience with that cartridge, but a relatively light 30 cal projectile is going to drop quite a bit and I think you'll appreciate the extra elevation.

It's probably easier to work in angular measurements for everything and leave inches out of it. Hornady 4dof or AB calculators are pretty good and easy to use.

 

[AuNEagle]

Any recommendations on a 36mm, 30 MOA mount? Spuhr goes from 20 MOA to 55 MOA (wow).

 

[BikePilot]

I'm running a 20moa Spuhr on a 20moa rail. I haven't looked for a 30moa mount.

 

[AuNEagle]

I should have thought of that. Thanks.

 

[Glassaholic]

I run a 20 MOA ERA-TAC on a 20 MOA rail for my ZC420. IQ is still excellent even at the extreme of travel, part of the design of the ZCO. Don’t worry about the ZCO being out of center, it performs better than many lesser scopes at the extreme than they do in the center. I conducted some preliminary testing on a resolution target at the extreme elevation setting and still had a phenomenal image. So getting a 20 MOA mount and being 6 mil off center is not going to hinder your IQ one bit with this scope.

Also, try not to get too hung up with inches, most ballistic calculators will give you drop in mils which is what your scope is made for. Once you get away from inches and use the ruler in front of you (the reticle) you’ll be much better off.

 

[Huskydriver]

Another 20 moa mount with a 30 moa rail.. Have 31 mils of the 35 available

 

[Glassaholic]

Any recommendations on a 36mm, 30 MOA mount? Spuhr goes from 20 MOA to 55 MOA (wow).

Don’t know of any but ERA-TAC makes an adjustable incline mount that you can dial any cant between 0-40 I think, but these mounts are big and expensive, I think the 20 MOA ERA-TAC or Spuhr would suit you just fine.

One other thing to consider, there is not much picatinny on an AR-15 size upper which I believe the HAM’R uses so you might need to get a cantilever mount. Keep that in mind as there are very few 36mm options that are cantilevered.

 

[TheOE800]

Don’t know of any but ERA-TAC makes an adjustable incline mount that you can dial any cant between 0-40 I think, but these mounts are big and expensive, I think the 20 MOA ERA-TAC or Spuhr would suit you just fine.

One other thing to consider, there is not much picatinny on an AR-15 size upper which I believe the HAM’R uses so you might need to get a cantilever mount. Keep that in mind as there are very few 36mm options that are cantilevered.

Tier One makes a cantilevered 36mm monomount in “medium” height. Spuhr also has a cantilevered 36mm if I’m not mistaken. I don’t think either is canted.

 

[Glassaholic]

... I will initially be zeroing the scope for 130 gr. Speer HAM’R HOT-CORE rounds (2510 fps, 18” barrel) ...

From what I’ve read here, the recommended starting point is 1/2 the elevation adjustment range of the scope which in the case of the ZC420 is 35 mil / 2 =17.5 mil.

The bullet drop calculations from the JBM Ballistics Trajectory-Drift calculator:

0” @ 100 yards
-6” @ 200 yards
-22” @ 300 yards
-53” @ 400 yards
-103” @ 500 yards
-180” @ 600 yards
-291” @ 700 yards
-440” @ 800 yards
-635” @ 900 yards
-880” @ 1000 yards

Just to clarify a bit more on my statement about inches vs. mils, I used the ballistics you provided above and ran some average atmospherics into the Berger calculator (https://bergerbullets.com/ballistics-calculator/) and this is what I come up with using the BC for the Speer Hot Core 130gr

Based on the above data, your theoretical maximum with a 0 MOA cant will be 900 yards (this will vary based on your atmospherics). I can see this from the column Elevation (mils) which shows drop at 900 yards of 17.20 mils and since half of the scopes total elevation (35 mils) is 17.5 mils as you said, this should give us a theoretical limit. I say theoretical because rarely are you able to zero perfectly within the middle of the elevation, even with 0 cant, there is usually some tolerance +/- so once you do zero your scope for your ammo, set the zero stop and spin those turrets to the top to identify just how much elevation you have from zero. But even at your elevation max, remember you still have the reticle to use as well

 

[AuNEagle]

Thanks for the feedback everyone.

I discussed a cantilevered mount with Richard at CS Tactical when I ordered the scope. It was his opinion that I wouldn't need one even though this rifle is an AR-15. So I'm trusting him at this point. And I'm sure if it turns out to be an issue he'll work with me to get it right.

Also, thanks for the advice regarding using angle measurements rather than inches for bullet drop. I didn't notice it at first, but both of the apps I used were able to output the bullet drop in mils which obviously would have saved me some math as I already knew the elevation adjustment range of the scope in mils. On the other hand, I'm a mechanical engineer by trade and a glutton for mathematics (punishment to a lot of people). And that little exercise did solidify my understanding of the relationship between inches. mils, and MOA. But I see how much simpler mils will be to use in the field (the ruler in front of you).

While we are kind of on this topic, I am considering downloading (buying) the Applied Ballistics phone (Android) app. Is that a good choice or are there better options? (If I need to post this last question in a different forum, please let me know.)

 

[Surly]

I opted for the 0MOA Tier-one mono mount. It will be going on a 20MOA base. This should meet my needs for now...

 

[Glassaholic]

Yes, Richard will definitely take care of you, so if the regular mount doesn't work to give you the proper eye relief (remember you don't want the mount forward of the upper picatinny rail even though the handguard looks flush, it is not a good idea to have part of the mount on the handguard and part on the upper) then return the mount he suggested and ask for the cantilever Spuhr.

With regard to ballistic apps, I highly recommend getting a Kestrel with applied ballistics built in, the 5700x/Elite is their top of line but if you only have a couple guns you can find the Sportsman or Ballistic series for a bit less (and can upgrade via firmware to the full Elite version later if need be). If you ever think you'll get a LRF like the Sig Kilo series or the Leica .com series, you'll want to make sure you get a Kestrel with bluetooth (Link) as you can sync these devices up to make for very quick solutions in the field. If you want a great comparison between the two units I've found Sam's review at Panhandle Precision to be excellent, and his video helped me greatly with figuring out how to set everything up:

Kestrel 5700 Sportsman: Review

We were set up on a Wyoming plateau as the sun broke the eastern horizon. Below us, a herd of antelope slowly grazed toward a distant fence line. As the lone pronghorn fell in line behind them, I r…

panhandleprecision.com

But if all you want is an app for now, Applied Ballistics is great. I think I have 5 different ballistic apps on my phone, but with the Kestrel and my Leica 2700.com I rarely use these apps anymore except for Ballistic-X, the reason I like this app is it has a feature that allows you to take a picture of your group on paper or steel and you can measure right on your phone, here is an example

(disclosure, this is the best 5-shot group I've ever shot and definitely not the norm for me, I'm usually a .5 - .75 MOA shooter )