This is one of the last posts covering the detailed data collected over the past 4 months for an epic scope field test focused on long-range, tactical rifle scopes in the $1,500+ price range. This represents an unprecedented, data-driven approach to evaluating the best tactical rifle scopes money can buy. Hundreds of hours have gone into this research, and both the scope line-up and the tests I conducted are built on advice and feedback from some of the most respected experts in the industry. My goal with this project was to equip fellow long-range shooters with as much hard data as I could reasonably gather, so they could see what they’re paying for.
I’ve already touched on optical performance, ergonomics, reticles, advanced features, and warranties. This post looks at mechanical performance, including how precisely calibrated the adjustment clicks were, internal adjustment range, travel per revolution, and other aspects. I surveyed over 700 shooters, and mechanical performance was rated as the most important feature of a scope. In fact, mechanical performance received 30% more votes than optical performance. A scope that doesn’t track, or have repeatable adjustments seems to be viewed as the biggest flaw a scope could have.
Mechanical performance is a critically important topic, but has been largely neglected in the shooting press. Here is what Dennis Sammut, Founder/President of Horus Vision, has to say on the subject:
“Yearly, a virtual mountain of written information is spewed forth from the word processor of gun writers. … When the subject is “riflescopes,” the writer’s primary focus is on external looks, dimensions, weight, reticle, image resolution, power range, and similar physical characteristics. It is impossible to find an article that evaluates a particular riflescope or runs a test on a group of a riflescope’s ability to accurately respond to elevation and windage knob adjustments.
Since long-range shooting requires elevation and windage adjustments to accurately engage distant targets, it is apparent that a riflescope’s elevation and windage adjustment knobs have to yield precise and accurate adjustments. When a rifleman engages distant targets and misses, he usually blames the ammo, the rifle, and finally himself. The riflescope is almost never looked at as contributing to errors. The rifleman has spent a lot of money on his riflescope. He falsely assumes it is a perfectly calibrated optical instrument for shooting.” – Dennis Summat
Well, Dennis you got your wish! I talked to Dennis a few months ago as I was planning this test. He has a ton of experience in testing the mechanical precision of riflescopes, and was a wealth of knowledge. In fact, Dennis created an entire line of calibration targets, which are designed to be a simple, inexpensive way to reveal any flaws in a scope’s mechanics (more on those later). He was very excited to hear someone was thinking about performing a serious evaluation of mechanical performance, especially when it involves such a large sampling of the best scopes available. It is surprising how little has been written on this topic, and I originally thought that could be because they all perform so well that there wasn’t a lot to differentiate between or talk about … wrong. I found a surprising amount of variance among the 18 scopes tested, so let’s dive into the results.
Precisely Calibrated Clicks
If you’ve read any of Bryan Litz’s books, you know how much he stresses the importance of actually checking to see if your scope tracks as advertised. It’s such a notable topic, Bryan talks about it several times, and here is just one excerpt from Applied Ballistics for Long-Range Shooting:
“If you need to adjust the scope by a precise amount in order to account for gravity drop on a long range shot, it’s imperative that you know exactly how much your crosshairs actually move when you turn the knobs. Simply assuming that each click is what it’s advertised to be is a bad policy, and will cause misses at long range. What’s worse, this problem can erode a shooter’s confidence in his firing solution, and leave him guessing about how much to adjust his sights.” – Bryan Litz
Bryan hits on this subject again in his 2nd book, Accuracy and Precision for Long Range Shooting:
“Un-calibrated sight adjustments are one of the most common problems in long range shooting. Many shooters take for granted that when they dial up or hold a certain correction in a reticle, that they’re getting exactly the intended correction. In real life, it’s more often the case that there is some amount of error in a scopes turret or reticle. … The reality is; that dial or reticle, like every other measurement instrument, needs to be verified before it can be trusted.” – Bryan Litz
Did you catch that? Bryan said more often than not, scopes have some amount of error in them. This test was designed to quantify that error, and I feel like it did that extremely well. It produced a clean set of data that was completely repeatable. In my continued tradition of 100% transparency on where this data came from, first let me explain how I performed the tests.
The Mechanical Calibration Test Method & Setup
The basic idea of how I would test this started with a relatively simple test Bryan defines in two of his books, which is referred to as the tall target test. The test goes something like this:
- At a measured distance of 100 yards, set up a 4 foot tall target with the aim point near the bottom.
- Using a level, draw a vertical line extending from the aim point to the top of the target.
- Fire a 5 shot group at the aim point with your 100 yard zero.
- Adjust the scope up 10 MOA and fire another 5 shot group.
- Adjust the scope up 10 more MOA and fire another 5 shot group.
- Adjust the scope up 10 more MOA and fire another 5 shot group. At this point, you should be hitting 30 MOA above your aim point.
- Measure the distance between the centers of the groups and see if they’re truly 10 MOA apart (should be 10.47” at 100 yards).
This approach is an outstanding test, and what most shooters to do. However, since this is an extreme field test, I changed a few aspects to ensure that the data collected was as complete and accurate as possible.
First, I removed the inherent dispersion of the rifle, ammo, and shooter from the equation. Although, I have custom rifles capable of averaging 0.3 MOA groups, even with that tiny spread the exact center of the group could still vary by a fraction of an inch in one direction or another from the precise spot the scope was pointing. Instead of mounting the scope on a rifle, I placed it in a Spuhr mount, and attached that to a custom fixed mount. This was essentially like putting it inside a vise, and it allowed me to manipulate the knobs up and down with the scope body held securely in a fixed position. There was no play in the mount, which was further confirmed by completely repeatable results, regardless of how many times I performed the test. The idea for this mount came from Tim K at Sniper’s Hide.
I decided early on to use Spuhr mounts for all of the mechanical tests, because I believe they’re the most rock-solid mounts money can buy. I’ve used them on my personal rifles for a couple years, and they’ve proven themselves in the field. Although Spuhr mounts are expensive (typically around $400), I wanted to go to extreme lengths to know with certainty that any point of aim shift recorded was NOT due to movement within the mount. Spuhr mounts provide that confidence.
Spuhr mounts have a couple features that were especially helpful for these tests. First, they’re a one-piece mount that are precisely machined from a single billet of aluminum, which means there is no need to lap the rings. The rings are perfectly aligned, which ensures more surface contact with the scope tube and also prevents stress on the scope tube, which can dent the tube, distort the reticle, and cause adjustment problems. Spuhr mounts also feature a bubble level built into the rear of the mount, which I used to ensure the mount was completely level during the tests.
Although Spuhr offers 29 different models of one-piece picatinny mounts, there were a few scopes with irregular dimensions that wouldn’t work in a standard size mount. The Valdada IOR RECON Tactical 4-28×50 has a proprietary 40mm tube, so I used the rings made by American Rifle Company Valdada included to mount that scope. The US Optics ER25 5-25×58 has an unusually long turret box, and it wouldn’t work in any the 6 Spuhr mounts I had. So I used the US Optics rings they provided to mount that scope. While these other rings may not have all the bells and whistles of the Spuhr one-piece mounts, they seemed very solid and the manufacturers obviously believe in them (because it’s what they sent me for testing).
Instead of a 4 foot target with a hand drawn line, I used Horus Calibration and Training System (CATS) Targets, which were designed for testing optical equipment just like this. For this test, I used their 0280F MIL/TMOA Series targets, which are enormous at 8 foot tall by 3 foot wide. They feature a 25 mil ladder (and an 83 MOA ladder) in the vertical direction. This target was specifically designed to validate the accuracy and repeatability of the numerical values and the click adjustment on a scope’s elevation knob. It also provides an extremely accurate method to check cant.
Horus has their CATS targets printed by a drafting company, instead of a typical printing company. Although drafting companies are much more expensive, they have intense tolerances to ensure the scales are ridiculously precise.
The enormous CATS target allowed me to more than double the elevation range tested. Since all of these high-end scopes are designed for long-range, I didn’t want to just test up to 30 MOA. Instead, I tested in 5 mil increments up to 20 mils (i.e. 5 mils, 10 mils, 15 mils, and 20 mils). I had similar increment sizes for the few MOA scopes I tested, with those going up to 70 MOA. 20 mils is 72” at 100 yards, and 70 MOA is 73.29” at 100 yards. And the Zeiss Victory scope actually had clicks that were 1/4 inch at 100 yards, which is more commonly referred to as Shooter’s MOA. I found a way to accurately calibrate that scope using this target as well. So the elevation adjustments tested were similar regardless of the units. Any error present in a scope’s adjustment is compounded with each turn of the turret, so I wanted to push these scopes to see what they’re capable of.
The setup of this test is extremely important. First, the distance to the target has to be precisely 100.00 yards. To do that I used a Leica Disto E7400x Laser Distance Meter, which is accurate to ± 0.1 mm. That should do! This isn’t a typical rangefinder, because it only reads out to 400 feet. It is a precision instrument used in the construction industry, and it’s far more accurate than using a steel tape or survey chain that could deflect or follow the contour of the land.
So, do I measure that from the scope to the target or the muzzle to the target? I’ve read that different scope manufacturers may use different approaches on this, so their calibration could be tuned towards one way or the other. Luckily, the guys at Horus had already thought a lot about this, and had a good approach itemized in the user manual for their calibration targets:
The question usually arises: Do I measure from the middle of the riflescope or from the muzzle to the target? Both are equally important as the rifle does the shooting and the scope provides calibration adjustment. To resolve this issue, establish an imaginary point located midway between the middle of the scope and the rifle muzzle. If you place your rifle at this shooting position, you have approximately ±10 inches to adjust your rifle to a comfortable position. Remember, there are 3600 inches in 100 yards; this 10 inch zone produces a +/- error of approximate 1/3 of 1% (= .0033).
Since I wasn’t mounting on the scope on a rifle, I didn’t need the ± 10 inches of variance to adjust the rifle, so this should be even more accurate than what was explained above. I simply setup my fixed mount so the scope would be the correct distance behind that imaginary line. I used a common 24” barrel for calculating the exact distance.
It is not only important to ensure the target is perpendicular with the shooter (see right angle in previous diagram), but the vertical ladders on the grid should also be precisely vertical as well (see right angle in the next diagram). That ensures if the scope is level, it should track straight up the line on the target. Once again, a very long level was used to set and double-check that the target was vertically plumb.
I also “broke in” the scope knobs before I started any of these tests, by rotating each knob through its entire range 50 times! This ensures any quirks from new, stiff mechanics should be settled down. I’m not sure there would be any on these high-end scopes, but I definitely didn’t want to take a chance of it skewing the results.
Each scope started at the bottom of its elevation travel. Once I had a scope secured in the fixed mount, I aligned them with the 20 mil reference line towards the top of the target using fine adjustments built into my custom fixed mount. You can see what the view from the scope looked like in the diagram below. When the crosshairs were perfectly aligned with the 20 mil horizontal line and the center vertical line, I would start turning the elevation knob to increase the adjustment. When you increase the elevation adjustment on a scope, this causes the reticle to lower on the calibration target. This might sound counterintuitive, but if your reticle goes down you have to raise the barrel to get to the same aiming point, giving your trajectory more arch. I’d continue to turn the knob until the crosshairs were aligned with the mark that was 5 mils below the original aiming point. Once I was satisfied that the crosshairs were perfectly even with the 15 mil mark (as shown below), I’d raise my head and see how many clicks it actually took on the turret to get that 5 mil adjustment, and I’d record that value. Sometimes it might be exactly 5.0 mils, other times it might be 4.9 or 5.1. Occasionally the crosshairs might be just short of the line at 4.9 mils, but past it at 5.0. In those instances, I’d record 4.95 mils to indicate the precise adjustment was “in between clicks.”
After the first 5 mil adjustment, I’d get back behind the scope and continue to turn the knob until the reticle was perfectly even with the 10 mil line on the target. Then I’d look up and record how many clicks it actually took to get it there. I’d repeat this for 3rd and 4th adjustments.
This “no live fire” approach worked well because all of these scopes have extremely high magnifications. If you were testing a typical 3-9x hunting scope, this may not have worked. But the lowest power scope in my group was 18x, with most around 25x and some up to 30x. Even at 18x, you could still clearly see the Point of Aim (POA) with precise granularity.
This seemed like a very clean approach to testing mechanical calibration, especially because each time I adjusted the scope to a point on the calibration target, I wouldn’t raise my head to check the knob until I was satisfied the crosshairs were perfectly aligned. This seemed like a very honest approach, and ensured I wasn’t inserting some kind of bias into the results. I ran through this test at least twice for every scope, and found my results were completely repeatable. This gives me a lot of confidence in the data.
While several scopes performed very well, only 4 scopes were perfect all the way through 20 mils of adjustment:
I can’t say how impressive that is. After I had tested several scopes from big-name brands, I started to doubt whether it was even possible for a scope to be 100% accurate all the way out to 20 mils. I was recording variances down to a ½ click, which was 0.05 mils on most scopes. So at the extreme adjustment of 20 mils, that means an error as small as 1/4 of 1% was identified (0.05 mils ÷ 20.0 mils = 0.0025). But, even with that absurd level of scrutiny, there were still 4 scopes that were flawless all the way through 20 mils of elevation adjustment. Wow.
Most of the scopes had adjustments in mils/mrad, but a few were MOA, and the Zeiss Victory scope was actually in Shooter’s MOA. All were tested to approximately the same amount of overall travel and increments.
Once again, you can see the Hensoldt, Kahles, US Optics, and Valdada all tested perfectly at 5, 10, 15, and 20 mils. But, you can see most of the scopes tested very well. The Leupold Mark 6 was only off by 1 click at 20 mils, and the Leupold Mark 8 was just 1/2 a click off at both 15 and 20 mils … which is very close to perfect. The Nightforce BEAST was off 1/2 click at 10 mils and 15 mils, and a full click at 20 mils. The Nightforce ATACR was dead on at 5 and 10 mils, but was off by 1 click at 15 mils and 1.5 at 20 mils.
I asked Nightforce how much the erector tube actually moves inside the scope body with each click of the turret, and while they said the exact amount varies by model, it would be around .007 inches per click for these scopes. That means that with each click the erectors are moving the tube by the width of a single hair. Honestly, considering that each click is making those microscopic adjustments, most of the scopes performed impressively … although some were better than others.
Many shooters don’t need to adjust beyond 10 mils, because that is enough adjustment to take most modern cartridges to 1,000 yards. Here is a little larger list with scopes that performed perfectly up to at least 10 mils:
- Hensoldt ZF 3.5-26×56
- Kahles K 6-24×56
- Leupold Mark 6 3-18×44
- Leupold Mark 8 3.5-25×56
- Nightforce ATACR 5-25×56
- US Optics ER25 5-25×58
- Valdada IOR RECON Tactical 4-28×50
And here are few scopes that were very close to perfect up to 10 mils. These scopes weren’t off by more than a 1/2 click at either 5 mils or 10 mil adjustments, which is still great performance:
- Bushnell Elite Tactical 3.5-21×50
- Nightforce BEAST 5-25×56
- Nightforce NXS 5.5-22×50
- Schmidt and Bender PMII 5-25×56
- Valdada IOR 3.5-18×50
- Steiner Military 5-25×56
You might notice that the Leupold Mark 6, and Nightforce ATACR both have “2nd scope” by their label, and the March 3-24×42 scope has “Average of 2 scopes.” The first time I ran through the mechanical tests, those 3 test scopes showed more error than others in the test. I thought the results might be a result of a defective unit, so I contacted each manufacturer. First, I completely understand that it is impossible (and impractical) for every scope to be perfect, so I always want to give a manufacturer a chance to fix something like that before I publish results that may not be representative of the typical unit. At the same time, I’m committed to being completely transparent and honest with my readers. So if I run into something like this, I give the manufacturer a shot at fixing it, and then in the article I mention the issues I ran into and how it worked out in the end. That seems like the most respectful and fair approach for both the manufacturers and readers.
So Leupold, March, and Nightforce were all kind enough to send me another test scope (I didn’t have time to wait on the units I had to be repaired, since this project was already running behind schedule). When I retested the new Leupold Mark 6 and the Nightforce ATACR scopes, they both performed considerably better than the original scopes. The first Leupold Mark 6 had an average of 3.7% of error in the elevation adjustment through 20 mils, while the replacement performed stunningly with an average of just 0.1% of error. The Nightforce ATACR followed suit with the original coming in with an average of 1.8% of error in the elevation adjustment through 20 mils, and the replacement coming in with 0.4% of error. In both of those cases, I feel like it was an issue with the particular scope and the original results were not indicative of what you can reasonably expect from Leupold or Nightforce. Either of those companies would quickly repair any scopes that performed like the original set of scopes I tested. So in both cases, I’ve only included how the second scope performed in the charts and scoring.
However, the replacement March scope that Kelbly.com sent unfortunately didn’t follow that same pattern. In fact, while the 2nd March scope performed similar to the original, it was actually slightly worse overall. The original scope had an average of 2.2% of error in the elevation adjustment through 20 mils, and the replacement had an average of 2.7% of error. I really didn’t know exactly what to do with those results, because with similar results this didn’t seem to simply be due to a defective unit like the Leupold and Nightforce scopes. I decided the best approach was to simply average the results from both scopes and publish that as my results for the March scope.
Here is another way to look at the same data. In this chart, I looked at what percent each scope was off at each of the 4 adjustments and then averaged those together.
One note here is that the Zeiss Victory Diavari 6-24×56 didn’t have enough elevation travel to reach the 4th adjustment. It had less overall elevation travel than the other scopes, and only adjusted 58” at 100 yards. The 4th adjustment here was around 72” at 100 yards. I didn’t want to decrease the range I was testing all the other scopes at just because the Zeiss didn’t have enough travel to get to the last adjustment, so I averaged the 1st, 2nd, and 3rd adjustments for the Zeiss here and just wanted to note that.
Does a 1% error matter?
While 1% isn’t much, this might depend on who you ask. Let’s look at a practical example to wrap our head around what that means. If it takes exactly 10.0 mils of elevation adjustment to hit at 1,000 yards (ballistics similar to a 308 Win), what does a 1% error do to our point of impact?
For this example, 1% error essentially means you’re off by 1 click, and 2% error would be 2 clicks off. If you were shooting at a relatively small 1 MOA target, being off 1% would still result in a hit … as long as you perfectly accounted for all other variables. It would be 1.5” from the edge of the target, so there isn’t much margin for error. At 2%, you’d be well off target. In this example, a 1.5% error would push you off the edge of the plate.
Here is another example showing a 1.5% error for a 20 mil adjustment at a 1 mile target (ballistics similar to 338 Lapua Magnum). This example is shown with a larger 2 MOA target, since that’s more typical at that distance. You can see you’d be off plate at that distance, even on the larger target. Being off by 1.5% of 20 mils, is the same as being 3 clicks off (assuming 0.1 mil clicks).
Although we’re talking about small numbers, there could be a hidden danger with these small errors. Bryan Litz explains:
“The importance of understanding sight adjustments can be illustrated with a very typical example that’s played out countless times in all disciplines of long range shooting. Let’s say a serious shooter diligently measures his muzzle velocity and all the atmospherics for his given location. He’s using a very accurate BC (hopefully referenced to the G7 standard), and he’s accounted for the sight height and even knows the cold bore zero of his rifle. He’s got a target at 1000 yards, and the carefully generated, ultra accurate firing solution tells him his bullet will have 314.1” of drop, which is exactly 30 MOA at that range. So he carefully turns his scope knobs up 30 MOA and fires. As he watches his bullet sail 2 feet over the target, he scoffs at the supposed accuracy of his expensive software and PDA and gives up on the possibility of reliable trajectory predictions altogether. The fall of the shot is noted in a log book, and revered as the true drop of the bullet at 1,000 yards for that rifle in those conditions, while the firing solutions of the PDA are from that day on, treated as an unreliable guideline of uncertain accuracy.” – Bryan Litz in Applied Ballistics for Long-Range Shooting
Even if the error isn’t enough to throw you off target, it still makes you question the accuracy of your ballistic solution. Error in scope adjustments is one of the most common reason someone’s firing solution doesn’t match up with their impacts in the field. Most shooters immediately start changing the inputs of their ballistics until it matches the number on the turret when they got a hit. They call it truing, but really, they’re adjusting the solution to better fit their erroneous turret. This can actually work … mostly. But it can also have unintended consequences, not the least of which is undermining your confidence in the computer-generated trajectory predictions.
Actual Results May Vary
I want to make it clear that these results shouldn’t be taken as universal. I tested one or two scopes of each model, and while this may provide a rough, ballpark idea of the mechanical calibration you can expect from different brands … you shouldn’t assume every scope will match these results. Actually testing your scope using the tall target test is one of the first steps of any serious shooter. There is no substitute for knowing how your scope tracks.
Other Post in this Series
This is just one of a whole series of posts related to this high-end tactical scope field test. Here are links to the others:
- Field Test Overview & Rifle Scope Line-Up Overview of how I came up with the tests, what scopes were included, and where each scope came from.
- Optical Performance Results
- Ergonomics & Experience Behind the Scope
- Part 1: Side-by-side comparisons on topics like weight, size, eye relief, and how easy turrets are to use and read
- Part 2 & Part 3: Goes through each scope highlighting the unique features, provides a demo video from the shooter’s perspective, and includes a photo gallery with shots from every angle.
- Summary: Provides overall scores related to ergonomics and explains what those are based on.
- Advanced Features
- Reticles: See every tactical reticle offered on each scope.
- Misc Features: Covers features like illumination, focal plane, zero stop, locking turrets, MTC, mil-spec anodozing, one-piece tubes
- Warranty & Where They’re Made: Shows where each scope is made, and covers the details of the warranty terms and where the work is performed.
- Summary: Overall scores related to advanced features and how those were calculated.
- Mechanical Performance
- Summary & Overall Scores: Provides summary and overall score for entire field test.