Drag Variability Reduction Technology
Experience unrivaled ballistic consistency that produces smaller groups at longer ranges.
Introducing DVRT™ - Drag Variability Reduction Technology
Using Doppler radar and Schlieren imagery, Hornady engineers have developed and patented Drag Variability Reduction Technology (DVRT) to increase the uniformity of bullet drag from shot to shot, resulting in less dispersion at long range.
While analyzing thousands of Doppler radar drag curves, ballisticians isolated a bullet tip design that would reduce the variation in drag from bullet to bullet. Specifically, the meplat must be flat – not pointed – and the diameter of the flat meplat is a specific ratio to the bullet diameter.
Upon refinement of this design feature in late 2018, DVRT was implemented into all bullets using the Heat Shield® Tip and the A-Tip® Match bullet. While DVRT was patent pending, shooters quietly benefited from this design for several years.
Now, with the patent issued, we can publish the science and benefits of Drag Variability Reduction Technology.
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Products with Drag Variability Reduction Technology
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The Discovery
Many long-distance shooters will have experienced the long range “flier.” When shooting at short range, very small groups are common with precision rifle systems, but when shooting at longer ranges, many have observed shots impacting noticeably outside of the group. Without an attributing source many have described them as an anomaly - a “flier.”
In 2016-2017, during the continued implementation of the Heat Shield Tip, Hornady ballisticians started to correlate Doppler radar recordings to the “flier” that shows up on long range targets but was never present at shorter ranges. While analyzing drag curves of several consecutive shots, an irregular drag curve would be measured that differed from the rest of the test samples. Each time this was observed the impact of that shot was significantly different than the other shots of the group. Over the next year, testing continued to identify the cause of these errant shots across multiple bullet manufacturers.
In 2017, after extensive research and development, and thousands of shots fired over Doppler radar, Hornady engineers isolated the cause of the variability in drag. Upon this discovery, tens of thousands of shots were recorded in 2018 to define the aspects of the bullet that contributed to the measured drag variability. Ultimately, the ratio of the meplat size and its specific shape was identified as the primary cause of the bullet’s drag variability.
Drag Variability
Long range shooting has exploded in popularity in the last 20 years. This popularity, combined with the age of information, has provided substantial information and understanding regarding the more detailed nature of bullet flight. When attempting to impact a target at long range, each detail matters, particularly as the target distance increases. Drag variability is not a new concept, but it has lacked defining information compared to other metrics such as velocity variation, dispersion, bullet drag, or BC.
In simple terms, drag variability can be understood as the shot-to-shot variation in bullet drag. Just as muzzle velocity varies shot to shot, so does the specific drag of each bullet. Differences in drag will result in different rates of velocity loss as the bullet travels to the target. Although the distance to the target may be the same, these differences in the rate of velocity loss will alter the time it takes each bullet to reach the target. Variance in time-of-flight results in variable amounts of time exposure to gravity and wind, increasing long range dispersion.
Drag variability has many root sources and each can have varying degrees of contribution to the total drag variability. The main sources of drag variability are:
- Bullet shape and/or dimensions.
- Muzzle exit and/or wear state conditions of the bullet influenced by:
- Barrel dimensions, rifling form, and twist rate.
- Muzzle device (flash hider, brake, suppressor etc.).
To properly characterize drag variability of the bullet alone, some defining information must accompany any drag variability measurements. Since the total drag variability is the sum of contributions from the barrel and or muzzle device, the contribution of each must be accounted for to isolate the drag variability of the bullet itself. This can be challenging as there are no set rules that a given characteristic of a barrel or muzzle device will produce “x” amount of drag variability. The answer lies in the combination of the unique components being used: barrel, muzzle device and bullet. To make comparative testing of one bullet to another, testing must be conducted with control samples of bullets fired across multiple barrel and muzzle device configurations. Simply looking at a single test of a bullet out of a barrel makes it impossible to determine how much of the total drag variability measured came from each source.
Drag, Muzzle Velocity, and Dispersion
The shot-to-shot variation in drag itself is not the sole cause of the long range “flier.” To understand why the “flier” shows up sporadically requires accounting for the additional factors of dispersion and muzzle velocity variation.
Dispersion is the randomized pattern produced by shot impacts at a given distance, also referred to as grouping or cone of fire. A group of sufficient sample size will have shots that impact high, low, left, right, and varying degrees of in between. When tested at shorter range, the shot that is highest in the group will continue to be the highest impact of the group at longer distances. The patterning of the shots will maintain orientation relative to the center but grow away from the center as the distance increases.
Muzzle velocity variation is the shot-to-shot variation that occurs in velocity and results in variability in the time it takes the bullet to reach to the target. The combination of two or more of these factors in the same direction is the source of the “flier.”
Shots that go high
Each of the three considered factors, drag, velocity, and dispersion can align to have an effect in the same direction. If the highest shot impact of a group is also the highest muzzle velocity, these two factors will work in the same direction making the shot impact higher. If the drag of this shot is on the lower end of the variability, it will impact higher yet. However, if the drag of this shot is on the higher end of the drag variability, it will move back toward the center and have some amount of cancellation of the effect of high velocity and corresponding highest impact within the group.
Shots that go low
The inverse of the prior example is the source of shots that drop well below the rest of the group at longer ranges. If the shot with the lowest muzzle velocity is also the highest drag, both aspects will increase the time of flight to the target and increase the time the bullet is affected by gravity resulting in a low impact. Combine this with the shot also being the lowest within the cone of fire of dispersion and this shot will impact lower yet.
Shot’s that go left or right
A shot that impacts left or right at long range is typically attributed to the effects of crosswinds. Although this is usually the largest contributor, the horizontal elements of dispersion cannot be ignored as a contributing factor. In no wind environments, some shots impact left and right of center naturally due to dispersion. If crosswinds are present however, their effect on the point of impact can far outweigh the left and right component of dispersion, especially at longer distances.
The horizontal impact shift observed when a crosswind is present is due to bullet drag. The higher the drag the more horizontal deflection will be observed from a given crosswind velocity. If a bullet had no drag (fired in a vacuum), there would be no crosswind effect. Wind deflection is a function of drag on the bullet. Therefore, if there is significant amount of drag variability from shot to shot, there will be a measurable difference in wind deflection within those shots, despite being fired in the same wind condition. Drag variability not only impacts shot locations in the vertical plane, but in the horizontal as well when crosswinds are present.
Frequency of the “Flier”
Outside of environmental factors, long range shot impact locations can be accounted for with high levels of accuracy if the variations in shot location (dispersion), drag, and velocity are known. All three aspects are at play for each shot and most of the time their individual high or low bias will cancel each other out. In other words, the infrequent and long held mythical “flier” can be understood and accounted for by the infrequent combination of known factors. Unfortunately, the shooter does not get to pick which shots will have higher, lower, or average drag, velocity, or shot location. Instead, the shooter must select components (bullets, ammunition, barrels etc.) that exhibit low variation in drag, velocity, and dispersion to increase hit probability or shrink long range dispersion.
Figure 1 provides a representative grouping at 1,000 yards. Color coded and numbered boxes highlight the distribution profile of the shot locations vertically. The center box (6) shows that most of the shots fall within its bounds. The table below the graphic shows the basic combination of factors that can result in a shot landing within the group distribution. The probability of average and/or high and low cancellations are 64% of the possible combinations, and portray the basic association of most of the shots landing within box 6. Boxes 3 and 4 are the result of the combination of two high or low factors and areas 1 and 2 are the combination of all three factors aligning in the same direction (high or low).
Figure 1.
The graphic of the 1,000 yd group and the corresponding number of shots in the numbered color boxes show a basic example of where the high and low “fliers” come from. The colored boxes and numbers correlate the combination of average, high, and low possibilities for impact, drag, and velocity.
The Benefit
By implementing the patented shape and ratios of the meplat and bullet diameter, Drag Variability Reduction Technology results in more consistent drag from shot to shot. This significantly reduces the chances of getting an impact within box 1 and 2 of Figure 1. and has a limiting effect on the outlying shots of box 3 and 4. This translates to consistently smaller groups at extended time of flight ranges. Drag Variability Reduction Technology was implemented into all Hornady bullets using the Heat Shield Tip and the A-Tip Match bullet in 2018-2019. Shooters have been benefiting from this technology for many years and many have reported that they do not experience the vertical “flier” that they do with other bullet designs. Notification of this improvement was withheld until the U.S. patent was granted.
Comparing Drag Variability
Comparing drag variability performance is an important consideration and can lead to decisions that have a large impact on long range dispersion capabilities. It is important to keep in mind that drag variability is a sum of contributions from the bullet, barrel, and muzzle device. The ability to gather conclusive data of one bullet compared to another requires significant and laborious testing. For generalized conclusions, each bullet must be tested across multiple, unique barrel conditions and muzzle device configurations to make a generalized statement as to being better or worse. In addition, this testing must be conducted with sample sizes that exhibit stability of results from test-to-test. If two different bullets are tested out of the same barrel, with the same load, on the same day, in the same conditions, a valid claim can be made regarding which bullet is better within those specific components. Making a broad conclusion based on this data would ignore the possible differing relationships that can exist across different barrels and muzzle device configurations. On many occasions, Hornady ballisticians have observed favorable drag variability of “bullet” 1 vs “bullet 2” out of “barrel 1,” and more favorable drag variability of “bullet 2” vs “bullet 1” out of “barrel 2.”
Environmental conditions can also play a role in the measured drag variability. Head or tailwinds that are present during drag measurements but are not accurately accounted for can result in higher drag variability measurements. Head or tailwind components will cause a change in the rate of velocity loss compared to no wind conditions. If the effects of wind are not accounted for, the measured data will show the wind induced velocity decay variability in the form of drag. This is particularly challenging when conducting long range drag testing as a level of wind uncertainty is nearly always present to some extent. To attempt to mitigate this uncertainty, it is imperative to conduct side-by-side testing in as close to the exact same environmental conditions as possible so that the uncertainty is equally present in both datasets.
Just as the presence of a head or tailwind can change the rate of velocity decay of a bullet, so too can bullet weight variation. If the weight of each bullet is not accounted for, and weight variation exits shot-to-shot, the rate of velocity loss will be slightly different even if the drag is identical shot-to-shot. Although the amount of weight variation is generally small in modern high-quality, long-range bullet manufacturing, it is worth noting. As a percentage, 1 grain of bullet weight variation of a 100 grain bullet is significantly higher than a 1 grain variation of a 300 grain bullet. If bullet weight variation is not accounted for, a perceived level of drag variability will be associated with the weight variation.
A Note on BC Variability
BC variability is not a synonymous term with drag variability in all aspects, assuming so can lead to invalid comparisons between bullets. Ballistic Coefficient is a single value used as a scaled reference to a standard drag curve to characterize the drag of a bullet. A given BC value is only valid for the point at which it was calculated at, or the average of a range of distance or time it is calculated over. Regardless of the method to arrive at a calculated BC, it is a single number. If the BC of a bullet is calculated at multiple different points in the bullet’s trajectory, the BC value will commonly change. This is normal and due to the mismatch in the standard bullet’s drag curve shape (Cd values) compared to the bullet being calculated. As such, a single shot can exhibit changes in BC value (variability) which can be counter intuitive. For variation to exist, multiple samples must be present to be variable. Within a single shot, the BC can and usually will change in BC value at different points, or over different ranges of time / distance. This is compounded by the relationship of BC to Mach number, or the speed of sound. Since most ballistic testing is done at a given range (distance), it is possible to conduct testing at the same distance but have two different ranges of Mach numbers represented simply by changes in air temperature. In other words, it is possible to conduct BC testing to 800 yds on a 90-degree day, and a 10-degree day and get changes in BC value and variation simply due to the differences in Mach number. The lack of stability of the singular BC value as a representation of a bullet’s drag must be acknowledged and accounted for when comparing shot-to-shot variation in BC.
Comparing drag coefficient (Cd) values at a given Mach number, or across a defined Mach number range is less prone to unassociated effects causing erroneous results. In the case of the BC test over 800 yards, the use of Cd vs Mach normalizes the differences in Mach number at different temperatures being masked as the same data over the same distance. Each data set at different temperatures will result in a difference in the Mach numbers the Cd values are measured over, even though the range distance is the same.