I apologize again for the lack of frequency in my posting lately. I still have a lot going on, and a moderately high constant level of stress, which has put the tasks of writing and making charts lower on the priority list. As always, when you notice that things seem to be back to ‘normal’, they probably will be.
Links to Individual Optic Test Results:
The intent of this final test was to take 4 shooting systems, manifested by the same rifle wearing 4 different scopes, to the commonly accepted limit of effectiveness of the 5.56 NATO cartridge, and determine the ease and accuracy that the systems (scopes) could be utilized to engage targets at distance. I should mention that I understand that there are good reasons to re-think the conventional wisdom on maximum distance of effectiveness of that cartridge, depending on application. In my case, the context of my shooting has been within the confines of the goal that I have set, which involves a 4” target within 200 yards. This test exceeded that distance, so this test viewed in that context can be classified as “long range”.
The idea of the test was to evaluate the scopes in terms of how well I could see targets at longer distances, how effectively I could use the reticles to hold over, and how easy it was to do those things. I tried to eliminate any variables that did not address those things. To that end, I shot from bipod prone with a rear bag and began in the shooting position with the rifle loaded, a round chambered, a spare mag within easy reach, my holdovers written down, and me wearing a diaper to eliminate the possibility of distraction for the 6 minute or so duration of the course of fire (and my new nickname is “Pampers”).
The target distances were 170, 230, 270, and 330, within a couple yards margin of error. The targets were arrayed in a different order, left to right, for every test. 9 shots were fired at each target, for a total of 36 rounds for each optic. The sequence of engagement, left to right, was optimized to balance the permutations of transitions from each target to each target, and this sequence was maintained for each optic. In other words, the physical order of targets changed while the shooting order left to right was maintained.
The targets were placed between a relatively narrow corridor, defined by a vehicle gate between a large field and a pasture, the gate being approximately 100 yards downrange. All of the targets were visible within a single sight picture, as my goal was not to test my ability to physically transition, but simply to align the sights on a new target with an appropriate hold and fire as quickly as possible. Actually, for each shot I needed to check the sequence number, verify holdover, acquire sight picture, press trigger, grab my pen, mark the shot on my sequence list, and repeat. The magnification for each scope was set at the maximum possible for the given scope.
The size of the ~4.188” targets in MOA at each distance, closest to farthest, was 2.35, 1.74, 1.48, and 1.21 (avg: 1.695 primary target diameter, radius: 0.8475). Note that the mean radius from the previous test over the course of 30 rounds per optic, in MOA, was between 0.834 and 0.968 (mean diameter up to 1.936 MOA, which means of course that some of the rounds were outside that diameter). That means that the dispersion of the average shot would put it outside the target at the 230 yard mark for all of the optics except the Z6i, even with an absolutely perfect zero (a rarity).
I have had samples of some ammunition shoot from this rifle with a mean radius in the 0.3ish range, so it could have been possible to increase my odds of success with better ammo, but as I noted previously, I only had sufficient quantities of XM193 on hand for testing. Would a finer comparison have been possible with better ammo? Probably, but I only have what I have.
My zeroes were fine tuned using the data from the previous test, which measured only precision (group location was irrelevant). I measured the deviation of the center of a 30 round shot group from the center of the target using On Target TDS and corrected accordingly. During that step I was wishing for finer adjustment increments in all the scopes with the exception of the SWFA, which has 0.1 mil adjustments. I would prefer even finer adjustments to get my zero just right. Instead, the scope makers are providing the scopes with coarser adjustments for the folks who like to dial and want to do it quickly. Or is it that they see the AR as a coarse instrument? I’m not sure, but for this application I would only touch my knobs for zeroing, and to my way of thinking, let me get the best zero I can. On the SR-4c, which has 0.2 mil adjustments, I went so far as to program the zero offset into my ballistic computer, because I just wasn’t happy with how close to center I could (couldn’t) get.
Each rifle system (as designated by the scope the X15 was wearing) was evaluated for accuracy, precision, with the measurement of speed noted to get at the element of ease. Accuracy was expressed by the deviation of the group center from the target center, as expressed in MOA. Precision was expressed as mean radius, also in MOA. Points on the target were measured, and serve as a combined measure of accuracy and precision. Speed will be expressed as an average split time.
After graphing the results I found that although the precision and deviation results were interesting, they don’t mean much separately. The points are much better in that it gives a total measure. I also will add a montage of each target at each distance and make a note of which scope is subjectively most intimidating as the one I’d like least to be shot at with. Take the last one how you will. There is often a fine line between brilliant and stupid.
170 yards. Target Size (5 point hit zone): 4.188”/2.35 MOA (radius = 1.175 MOA)
This target seemed pretty close subjectively. My holdover was only 0.1 mils. At this distance the precision for the scopes that I have good data for doesn’t show that significant a difference. The SR-8c was the most precise, but even with a perfect zero would not have been good enough to keep all the hits inside the ~4.2” target.
I’ll explain the format of the above graph, although I think it’s probably obvious. The wide bars illustrate mean radius. The narrow bars illustrate extreme spread. The target’s dimensions are illustrated on the right for comparison. All the values are in MOA.
The deviation showed that both the SR-8c and Z6i were very close to the point of aim, both well within the correctable amount of their turrets’ adjustment value. The SWFA had considerably more deviation. I look to the scopes’ reticles as the primary attribute that affected this measure of performance. Note that the SWFA scope has a floating dot in the open center of the crosshairs (that don’t cross). I think this may have made the rather small holdovers at the closer ranges less precise in terms of deviation.
The format of the deviation graph should be obvious, but also note that the scale matches the graph measuring precision above it (despite the difference in the frame size), so when they are both viewed together you could get some idea of what the group size was and how far off it was. Or just look at the targets, which follow.
The points showed that while the SR-8c and Z6i pretty much stayed together closely, the SWFA really fell off the chart. When you combine the worst precision with a considerable amount of deviation, the results really show in the points.
The actual targets are below. The first array is different than the rest in that they are out of the order I tested them, because the SR-4c was not a valid group due to some of the hits being off paper and not accountable. In the following photo the targets, left to right correspond with the following optics: SR-8c, Z6i, SWFA, and SR-4c.
For the “poking the head up out of cover” measurement, I count the SR-8c as the most intimidating, and the Z6i a close second. After that I rate the SWFA over the SR-4c.
230 yards. Target Size (5 point hit zone): 4.188”/1.74 MOA (radius = 0.87 MOA)
This distance was really the last point of comfort for the magnification level of all the scopes except for the Sr-8c. My hold at this distance was about 0.4 mils. It may have been 0.5 for the scopes that I used the lower Nightforce mount on, but I can’t remember for sure. For whatever reason, this distance was the Z6i’s opportunity to shine. This was the closest that any of the scopes came to having a group extreme spread that would fit inside the target.
Of course fitting the group in also depends heavily on how well centered it was. One constant with the Z6i was that its deviation from the target center was never more than 0.11 MOA, and in this case was 0.07 MOA!
This, predictably played out well in terms of points for the Z6i. I can’t say that it exactly dominated, because the SR-8c was close behind, both of them well ahead of the rest.
The targets from here on out will be, left to right, SR-8c, Z6i, SR-4c, and SWFA.
I would say that I find them from most intimidating to least, the Z6i, SR-8c, SWFA, and SR-4c, which in this case mirrors the point rankings.
270 yards. Target Size (5 point hit zone): 4.188”/1.48 MOA (radius = 0.74 MOA)
Something interesting began to happen at this distance. Note that all these were shot in a randomized “round robin” sequence, so it’s not really accurate to say that it “began to happen at this distance”, it just feels natural to say it that way. Anyway, the interesting thing was that the SWFA scope began to perform better and the Z6i started dropping off a bit. These are both 6 power scopes, so I find that interesting. I think the main difference is the complexity of the reticles- the SWFA is quite complex while the Z6i is quite simple. The SWFA also has an open center with a fine dot for aiming, which of course I wouldn’t have been using at these distance due to the holdover required. I think that the reason the SWFA started improving was that the holdovers at this range were well clear of the open centered portion of the reticle. Also note that the Z6i dominated throughout in terms of deviation of group center from target center, but tended to be worse as far as precision. The limited power of the SR-4c was also a huge liability at these distance with such a small target.
Oddly, I find the Z6i target to be most intimidating. I’m basically looking at hit rate here, probably for the obvious reasons. A hit rate graph would be nice wouldn’t it, but I’m sick of making graphs for the time being.
330 yards. Target Size (5 point hit zone): 4.188”/1.21 MOA (radius = 0.605 MOA)
The extra magnification of the SR-8c allowed it to dominate at this distance. The Z6i showed an incredibly low amount of deviation from target center to group center, sufficient to score it a decent amount of points, even with its less than stellar precision. The SWFA seemed to do fine while the SR-4c was just out of its element, not due to group size but due to deviation.
When taken as an average, the precision varied little between the systems, with the SR-4c lagging just a bit. What made the scopes perform better in general was the balance of low group deviation and precision. If the Z6i would have shot a bit tighter it would have ruled the entire thing, but the SR-8c just did a little bit better job of balancing everything.
The SWFA suffered by its relatively larger deviation, especially at the closer ranges. The fact that it performed comparatively better at longer distances indicates to me that the reticle is optimized for longer distances, which makes sense given its complexity. What is puzzling about that scope in my opinion is that with a 6 power maximum magnification it will never be optimized as a long distance optic, which, coupled with that reticle makes the scope something of an oddity.
The SR-4c, while a superb scope inside 100 yards, seemed to be simply outside its element. I should note again that the target I used is small for most uses, and that a person could probably double the distances for most applications.
Finally, I included the average split times of each optic to indicate ease of use. There really isn’t much difference. Note that the SR-4c wasn’t difficult to use for this test. It was actually easy because I just had to accept what I had, just like with irons. It just didn’t work as well as the scopes with adequate magnification for the task, as exemplified by the SR-8c. There must have been something about a 6 power scope, because they were the same down to the hundredth of a second.
If price were no object, I think that the obvious choice for rapid transitions at what most people would consider mid-range distances is the U.S. Optics SR-8c. It wasn’t always the best at each distance, but it was pretty consistently in the top (or close enough to still hang in there), and consistent enough across the board to score the most points. While I find the Z6i compelling for its amazing image and field of view, the simplicity of its reticle and because the second focal plane makes a lot of sense to me, it just seemed to lose its luster past the 230 yard mark for some reason.
I’ll sum up my thoughts of the performance of the optics as a whole in the next, and last article in this series. Thanks for reading.