Tag Archives: ballistic coefficient

RELOADERS CORNER: Understanding Ballistic Coefficient

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Math and myth both get involved in bullet Ballistic Coefficient discussions. Keep reading to separate the two and learn exactly what BC is, and what it isn’t. MORE

bc

Glen Zediker

Years ago I explained in great detail to a fellow here all about ballistic coefficient and how it was calculated and how it could be used and how it can change and so on, and he stopped me: “So you mean it’ll hit furtherer on up the hill…” That’s it.

A “ballistic coefficient,” or “BC,” is a number assigned to a bullet that suggests its aerodynamic performance.

That’s a key word, “suggests.” The main suggestion is how well this bullet will fly compared to that bullet, and the one with the higher BC ought to fly better. Fly better means less drop and drift, and those, factually, are a product of the higher-number BC. My best all-inclusive definition what a higher BC does for us: less speed lost over distance. Regardless of the muzzle velocity or the distance, one bullet with a higher BC will lose relatively less velocity over the same distance.

bullet blueprint
Here’s a blueprint. All the information needed to calculate a BC is contained here. It doesn’t have to be a real bullet because a BC model is not a real bullet either. Design factors that influence BC are virtually every design factor: length, ogive, boat-tail, meplat, weight. These factors, in this instance, calculate to a G1 BC of 0.560. By the way, there’s about a 5 point BC increase for each added 1 grain of bullet weight.

BC is calculated based on a standard bullet model. There are 7 of those. Two are normally used to determine BC for conventional rifle bullets, like what the most of us reading this use. Ballisticians and designers know which model to apply to different bullet types. The common model is a “G1” (another is G7, which is becoming the popular standard for boat-tail bullets; G1 is based on a flat-base). The flight of this G1 bullet has been calculated at varying velocities and distances. It’s “all math” because a G1 does not in fact exist. BCs are derived by comparison.

g1
The older standard for most rifle bullets was the G1. The newer, and better, standard is the G7. However! BC is never chiseled into stone regardless of the model. It’s a way to compare bullets, and a place to start figuring yours out.

g1 and g7

The standard bullet of any form-factor has a BC of 1.000. An actual bullet that’s compared to the model at points downrange will either be flying faster or slower than the model. If it’s moving faster, its BC will be greater than 1.000. If it’s going slower, it will be less than 1.000. It’s a percentage of the standard or model bullet’s performance.

Now. That is also all that it is!

BC is not an infallible factual statement about precisely what a bullet will be doing when it’s loaded and fired at that target than moment with that rifle. Not nearly, not hardly.

To me, BC gives us a place to start estimating drop (elevation) and also clues to how much it will get moved by a wind. It’s a way to compare bullets.

BC changes! Day to day, place to place, hour to hour.

Some bullet makers publish a BC for a bullet based on actual testing (chronographs) but now it’s pretty much “just math.” That’s fine. Which — math or measure — provides the best information? Some believe that a measured, tested BC is more realistic and, therefore, more valuable. But, if the point is to compare bullets, calculated BCs is more reliably accurate.

We (NRA High Power Rifle shooters) have gone to difficult and frustrating lengths to collect data to calculate “real” BCs (chronographing at 500+ yards hain’t always easy). Measured BCs are quite often lower, and they are quite often higher. Reasons follow.

The accuracy of drift and drop tables clearly revolves around what the actual, at that moment, BC performance is from the bullet you’re shooting (compared to what it’s “supposed” to be).

Anything that can influence bullet flight influences the actual, demonstrated BC performance.

BC uniformity is important. Bullets that show uniform BC performance produce less elevation dispersion. A source for variation is the meplat (bullet tip). Hollowpoint match bullets are notorious for inconsistency in this area. There’s a tool, a “meplat uniformer,” that fixes it. That’s pretty much the point to the plastic points on bullets like Hornady’s A-Max line.

Atmospherics, which add up as a list of factors, have a huge influence on BC performance. Air density is probably the most powerful influence. Any conditions that allow for easier passage of a bullet through the air don’t detract as much from its stated BC as do any conditions that serve to disrupt its headway. BCs are based on sea-level so can easily show as a higher number at a higher elevation. I can tell you that bullets fired at The Whittington Center in New Mexico have a noticeably better BC than those shot at Port Clinton, Ohio.

Range reality is that the demonstrated BC changes from morning to afternoon and day to day and place to place. The calculated BC is not changing, of course, but the mistake is assuming that a BC is a finite measure of bullet performance.

Bullet stability is even a factor. For a stated BC to be shown on a shot, the bullet has to be “asleep.” If it’s not stable, it’s encountering disruptions that will slow it down. The rotational speed of a bullet in a test can influence BC. We’ve seen differences comparing different twist-rate barrels, and the faster twists often show a little lower tested BC.

Factors that don’t matter in BC? Caliber. I’ve been argued at often over this next, but it is perfectly and absolutely true: BCs work the same regardless of caliber or bullet weight. Two bullets that each have a 0.550 BC, for instance, behave the same. That’s helpful, and at one time was more helpful than it is now. When we had to use paper tables to get drift and drop data and there was a new bullet that didn’t yet have those tables done, all you had to do was find data for another bullet with the same BC, go to the same muzzle velocity, and that data was 100-percent accurate. A .308 and .224 that both have the same BC share the same table. Remember, it’s not “real,” it’s a mathematical model.

So if you take a load to the target one day and you’re putting on more elevation than the BC-based calculation says you should, the BC isn’t wrong. The day is just different.

Finally, does it matter (really) if a bullet BC is based on a G1 or G7 model? Debates continue. But, not really, and I say that because BC is still only a suggestion. G7 is a more closely matched model to what we’re usually shooting when we think of a “high-BC” bullet, but all the same factors day to day also influence its accuracy. Given access to the data, I definitely, though, go with G7 calculations to have a place to start from. My experience has been that there is less difference in varying conditions, but, again, it’s still (plenty) enough change that you cannot dial it in and win anything…

The preceding is a specially-adapted excerpt from Glen’s book Handloading For Competition. Available HERE at Midsouth Shooters Supply. Visit ZedikerPublishing.com for more information on the book itself, and also free article downloads.

RELOADERS CORNER: Bullet Ballistic Coefficient

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Ballistic coefficient is a term that’s often used but sometimes not fully understood. Keep reading to find out exactly what it is, and what it isn’t…. HERE

nosler rdf
BC is essentially a race between a real bullet and a mathematical bullet. Real bullet never wins… The closer the real bullet gets to the “standard” bullet, though, the higher its BC and the better it’s going to fly. I’d love to get a Kroger-sack full of G1s… Until then, one of these Nosler RDFs will do nicely.

Glen Zediker

A “ballistic coefficient,” or “BC,” is a number that suggests a bullet’s aerodynamic performance.

BC is a component in bullet design that matters much, and it matters more the farther it travels. Bullets that flat out fly, fly flat far out, are of great interest to any longer-range shooter. A bullet with a high(er)-BC is also an advantage at shorter distances, especially when there are variations in the shooting distance. A flatter-shooting (one of the traits supported by a higher BC) bullet means a more flexible zero, a smaller difference in the elevation hold from, say, 100 to 300 yards. BC is influenced by sectional density, bullet weight, and, mostly, its shape or profile.

BCs are derived by comparison. Here’s how that works: There are “standard” bullets that are mathematical models. Bullet designers and ballisticians know which model to apply to different bullet styles. Pistol bullets, for instance, are calculated from (compared to) different models. For the majority of rifle bullets we’ll encounter, one common model is a “G1” (there are others, like G7, which is becoming the popular standard for boat-tail bullets; G1 is based on a flat-base). The flight of this G1 bullet has been calculated at varying velocities and distances. It’s “all math” because a G1 doesn’t exist in a tangible sense.

vld blueprint
Here’s a bullet blueprint. It’s the Bill Davis original 105gr 6mm “VLD” (very low drag). Design factors that influence BC are pretty much every design factor: length, ogive, boat-tail, meplat, weight. All these factors, in this instance, calculate a BC of 0.560. By the way, there’s about a 5 point BC increase for each added 1 grain of bullet weight.

The standard bullet has a BC of 1.000. An actual bullet that’s compared to, for example, the G1 at points, distances downrange, will either be flying faster or slower than the G1 model. If it’s faster, its BC will be greater than 1.000; if it’s slower, it will be less than 1.000. So it’s a percentage of the standard or model bullet’s performance.

Comparing bullets with different BCs, the one with the higher number loses less speed over distance. Losing less speed means its flight time will be shorter and it won’t drift and drop as much as will a bullet with a lower BC. So, a 0.600 flies better than a 0.550.

Depending on the bullet-maker, assigned or published BCs are either calculated or measured. More mathematics than I can wrap my mind around can get these calculations done based on a blueprint. Measured BCs involve chronographing at the muzzle and then at other points on downrange, same bullet, same flight.

Which method — math or measure — provides the best information? Some, and this only “makes sense,” believe that a measured, tested BC is more realistic and, therefore, more valuable. But, if the point is to compare bullets, calculated BCs might be more reliably accurate. I know a number of very serious NRA High Power shooters who have gone to great lengths to “field test” different bullets. It’s not easy to chronograph at long range. Given that information, measured BCs are quite often lower, but not nearly always. Reasons follow.

All the drift and drop tables (whether printed or digital) you’ll see are based on a bullet’s assigned BC. The accuracy of those tables clearly revolves around what the actual, at that moment, BC performance is from the bullet you’re shooting. Also, some bullets have a different stated BC based on muzzle velocity to start.

A whopping lot of things affect the actual, demonstrated BC: anything that can influence bullet flight influences the actual BC performance.

Bullet stability is a factor. For a stated BC to be shown on a shot, the bullet has to be “asleep.” If it’s not stable, it’s encountering disruptions that will slow it down. The rotational speed of a bullet in a test can influence BC. We’ve seen differences comparing different twist-rate barrels, and the faster twists often show a little lower BC outcome.

Atmospherics, which add up as a list of factors, influence BC mightily. Air density is probably the most powerful influence. Any conditions that allow for easier passage of a bullet through the air don’t detract as much from its BC as do any conditions that serve to hinder its flight. BCs are based on sea-level so can easily show as a higher number at a higher elevation.

uniformed meplat
BC uniformity is important to a long-range shooter’s score (less elevation dispersion results). There will be variations in any box of hollowpoint match-style bullets, and a source for variation is the meplat (tip). These variations are the result of the pointing-up process in manufacture. I’ve measured as much as 0.020 inches sorting through a box of 100. A “meplat uniformer” tool eliminates this variance. Uniforming reduces BC 3-4 points, but it’s a trade many serious long-range shooters say is worth the effort. Uniformed on right.

meplat uniformer

Range-realized reality is that the demonstrated BC changes from morning to afternoon and day to day and place to place. The calculated BC is not changing, of course, but the mistake is assuming that a BC is a finite measure of bullet performance. If you’re interested, there’s some valuable information from David Tubb (visit DavidTubb.com). He’s done a volume of work on calculating influences from atmospherics as it applies to his DTR project, which, in one way of seeing it, gets down to understanding why it’s really rare to dial in what a ballistics table says for a particular bullet and speed and distance, and hit the target.

One last (for now) bit of information I’ve always found valuable: a BC is a finite thing in one regard, and that is that any BC derived from a G1 model, for instance, fits all bullets with that same BC. This was helpful before ballistics apps were as common and easy as they are now. For instance, if there was a new .224-caliber bullet with an advertised BC, but no tables, just find another bullet, of any caliber, with that same BC, plug in the velocity, and the drift and drop figures will be accurate.

The information in this article is from Glen’s newest book, Top-Grade Ammo, available HERE at Midsouth. Also check HERE for more information about this and other publications from Zediker Publishing.

REVIEW: A Long-Range Story: Hornady 4DOF Ballistics Calculator

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Here’s a new ballistics calculator that takes four important ballistic factors into account, not just BC, to provide radically more precise calculated bullet flight figures. Here’s how it works…

4DOF

by Richard Mann

The new Hornady 4DOF ballistics calculator is so precise because it combines what Hornady calls the Four Degrees of Freedom. In other words, it takes into account windage, elevation, range, and angle of attack to generate a drag coefficient.

4 DOF

Recently, a few magazine editors visited for a week. Egos were on display and opinions were as thick as brass on the range at Gunsite Academy. The purpose of this get-together was to test about two dozen rifles, some purpose-built for connecting at extended distances. I have access to a 1,700-yard range and we spent the day there. My 17-year-old son, Bat, served as the official “range rat.”

After our 500-yard testing was complete, I told my associates I needed to get the DOPE (data of previous engagement) on my son’s African rifle. This would save a trip back to the range and give him some time behind the gun as payment for the support role he’d been filling.

The previous evening we had chronographed the Hornady Precision Hunter ELD-X load for the 6.5 Creedmoor my son would be using. That velocity, along with the bullet and related specifics were entered into Hornady’s 4DOF ballistic calculator, which is available online. I’d printed the results and our goal was to confirm elevation come-ups out to 500 yards. Amazingly, this was done with 5 shots; my son connected center target at 100, 200, 300, 400, and 500 yards. The data generated by the Hornady 4DOF calculator was spot-on.

Bat was having fun and shooting well, and since he now had the attention of the visiting editors, I figured, what the heck, he might as well try 700 yards. His first shot at 700 was about 2 inches high so he made a .25-MOA correction and fired again. Center hit! Now he really had their attention.

The next farthest target was at what I was told was 1,100 yards, and Bat asked if he could take a poke. I was skeptical and worried he’d blow the impression he’d already made on these experts, but figured the boy deserved a chance. The Hornady 4DOF ballistics calculator data called for a 38.25-MOA adjustment at 1,100 yards. I got on the spotting scope and told him, “Send it.” He did, and he missed high, by what appeared to be several feet.

I Instructed Bat to walk the reticle in the Bushnell 2.5-10X Engage riflescope — yes, this was a 10X riflescope — down 1 MOA at a time. At 3 MOA below center, I called the shot just left. (Wind is a terrible thing at 1,100 yards.) My instructions were to keep the same elevation hold but to also hold 2 MOA off the right edge. He pulled the trigger six times and achieved six hits. The onlookers were stunned, I however, was confused.

With the 4 DOF calculator from Hornady you can input your data and go to the range with total confidence it will be precise. Of course, remember, garbage in, garbage out. You have to input the right information.

4DOF printout

How could the Hornady 4DOF ballistics calculator data be so correct out to 700 yards and be off so much at 1,100? A range finder and a return to the Hornady 4DOF ballistics calculator answered the question. Instead of 1,100 yards, the target was at 1,048 yards. Resetting the Hornady 4DOF calculator to display come-ups in increments of 10 yards, it showed the proper correction for that distance to be 35.25 MOA. With our original 38.25-MOA correction we were 3 MOA or about 33 inches high. Had we known the correct range to the target, the 4DOF-generated data would have allowed for an easy first or, since we had a bit of wind, second-round hit.

What makes all this possible is the math and mechanics behind the Hornady 4DOF ballistics calculator system. Its four degrees of freedom, taking into account windage, elevation, range, and angle of attack, allow trajectory solutions to be calculated with a drag coefficient instead of a ballistic coefficient (BC). It’s also the first publicly available ballistics calculator capable of determining the accurate vertical shift a bullet experiences as it encounters a crosswind, which is known as aerodynamic jump.

By using Doppler radar and actually shooting bullets, Hornady calculates the exact drag curve for every projectile in the 4DOF Bullet Library. (Currently there are more than 100 projectiles from Hornady, Lapua, Berger and Sierra.) BC can change as velocity changes, a drag curve doesn’t. Explained simply, instead of using BC, which gives you a snapshot of a bullet at various distances; Hornady has created a video of the bullet’s flight. This allows the 4DOF calculator to predict drop with perfection at any distance, every time.

The takeaway from all this — the one that’ll matter to you and your ammo — is that the Hornady 4DOF ballistic calculator is extraordinarily precise. Taking data this exact to the field on a first try is as rare as 17-year-old boys who can hit at 1,100 yards, six times in a row.

Check it out HERE

Download the app HERE for iOS

Download the app HERE for Android

Shooting Skills: Shooting The Breeze, 3

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Putting it together: follow these suggestions and lose your fear of the wind!

Glen Zediker

Up to here we’ve talked over the influential factors wind brings with it. Here’s how to take it right back to the wind.

First, there are two essential “types” of shooters with respect to how they adjust for the wind on each shot. Dopers and chasers. I’m a chaser. A doper, wind doper, is one who carefully studies inputs and makes what amounts to a unique correction for each round fired. I say unique because it takes more time. They constantly evaluate and calculate the influence and often do much of it using one of the hand-held wind-meters talked about earlier.

I’m a “spotter-chaser,” which is actually a tad amount demeaning term branded on my style by the dopers. Technically I’m not really “chasing the spotter,” which means adjusting based solely on the position of the last shot. No. I’m anticipating a needed change based on observation between shots, but I’m doing it quickly, and I use the spotter location to confirm or modify my setting. That tells me if I’m seeing what I think I’m seeing. (A spotter is an easily-visible disk on a spindle that’s inserted into the location of the last shot hole by the folks pulling targets in the pits.)

Remember what was said last time about wind cycles? Usually there’s between 6-8 minutes before a cycle repeats, a little more or a little less. I want to get all my rounds downrange, if target pit service allows, during one cycle. Shooting into a build-up, watch for indications of a wind velocity increase. If the wind is moving left to right, I don’t want to see anything too close to the right edge of the 10-ring; I hedge a half-minute of angle or so to guard against losing a shot that direction if there’s an increase I missed, but not hedging so much that I’ll be too close to the left edge if I misread and overcorrect for a pick-up.

Pick one indicator, stay with it.

David Tubb
Most good shooters use mirage as their leading indicator to spot changes in the wind. With well-designed stand, the scope can be set it up where you can see the wind with the left eye and see the sight with the right without anything more than a visual focus shift. That gets the shooter back on the trigger with the least chance of missing another change. David Tubb demonstrates.

There are resources that give clues or evidence of wind direction and strength: wind flags, observation of grass and trees, and mirage.

Almost always I use mirage as my leading indicator. Mirage (heat waves) is always present but you’ll need a scope to read it. For 600 yards I focus my scope about halfway to the target. Mirage flows just like water and the currents can be read with respect to wind speed as well, but it’s not clearly accurate beyond maybe a 15 mph speed. The thing is that mirage shows changes, increases or decreases, and also direction shifts, really well.

A couple more things about mirage flow: when mirage “boils,” that is appears to rise straight up, either there’s no wind or the scope is dead in-line with wind direction. And that’s a quick and accurate means to determine wind direction, by the way, move the scope until you see the boil and note the scope body angle. It’s also how to know when a “fishtail” wind is about to change, a boil precedes a shift.

I use a long-eye-relief 20X to 25X wide-angle eyepiece. That setup shows the flow best. And pay attention to where the wind is coming from! See what’s headed your way, because what’s passed no longer matters. That’s true for any indicator. Right to left wind? Read off the right side of the range.

wind zero
Shooting into and through a buildup is a good strategy. My plan is to hedge against losing a shot “out” so I normally have an “insurance click” on to guard against missing an increase in wind value, and also hoping a sudden decrease doesn’t bite me and land one inside the wind. 10s win. Clearly, being able to honestly and precisely call a shot is a huge asset. That’s the only way to get good feedback from the last shot location.

Once I get on target then all I am doing is watching for changes. It’s really uncommon to make a big adjustment between shots. Once a string starts it’s ones and twos, back and forth. The fewer condition changes you are enduring, the easier it is to keep everything on center. That’s why I shoot fast, and that’s why I start at the low point in a wind cycle.

Speaking of getting on target. If it’s an NRA High Power Rifle event, you’ll get two sighters. I put my best-guess correction on before the first sighter, plus two clicks extra into the wind. Example: it’s quartering left to right and I’m guessing 2MOA, so that’s 8 clicks in the “left” direction, so I put on 10. That’s how I find out if I saw what I thought I saw. Then, and this is very important: Make a full correction off the result of that first sighter! Put the clicks on that would have centered that shot. The exception is if there was a notable change sensed between the first and second, but, even so, first sighting shot location lets you know if you got the value (what the wind is worth) under control. There’s one more round to go before you’re on record, so interpret from that and start the string.

sighter correction
Make a full correction off the first sighting shot location! Even if there are minor changes afoot, that’s how to know how well you assessed condition influence pre-shot. Don’t second-guess. After the second sighter you should be on target and then simply watching for changes. Pay attention, correlate visible cues to the results of prior shots, and if in doubt, click into the wind.

If you’re not at an organized event, having a spotter helps! Getting someone to watch for impacts while you shoot is a huge time-saver.

Information in this article was adapted from material in several books published by Glen Zediker and Zediker Publishing. Glen is a card-carrying NRA High Master and earned that classification in NRA High Power Rifle using an AR15 Service Rifle. For more information and articles available for download visit ZedikerPubllishing.com

Shooting Skills: Shooting the Breeze, 2

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Adjusting for wind effect first comes from collecting information. There are two main components and one very important key. These three steps are essential. Keep reading to learn more.


Glen D. Zediker


Learning to shoot well on a windy day involves inputs. A lot of inputs.

Pretty much: wind speed and wind direction are the combining key factors that determine how much sight correction or “hold off” (if you prefer) is needed to get to target center. Speed and direction inputs combine to make a decision on the correction amount. Speed and direction, in tandem, have compounding or offsetting influences on the amount of correction. If either changes, the correction changes.

For instance: if the direction changes and the speed stays the same or the speed changes and the direction stays the same, it’s just more or less correction. But it’s imperative to keep in mind that these are linked.

Most shooting ranges, if construction plans made it reasonably feasible, are set up facing North. That helps. Head- and tail-wind components are less influential than the cross-wind component.

1. Estimate Speed
Being a competitive shooter and, therefore, an admittedly unashamed gamesman, employing some sort of short-cut electronic trickery comes first to mind. A wind meter is the fastest and surest way to get a start on a number. There are very good hand-held meters available, and these range in cost, convenience, and complexity levels. Some provide vauable additional information (such as density altitude), the use of which will be talked on another time.

wind meter
Learning to read wind speed comes only from experience, but something like one of these Caldwell-brand units jumps the learning curve way on up in a hurry. It’s simple, accurate, and well worth the less than $100 it costs. This is the Cross Wind Professional Wind Meter. See more HERE.

Visible indicators are simply observations. If it’s a shooting range, and if there are wind flags, look at the angle the wind is standing a flag out to, divide that by 4 and that’s a close approximation of wind speed. Of course, that depends on the flag material, and so on. Wind flags mostly help sense direction.

I know this is a serious cop-out, but experience is really the only teacher. There’s an old-school wind estimation guide first published eons ago that provides some input on guessing wind strength based on environmental clues. Click HERE to download an updated copy of the “Beaufort Scale.”

Stop! The wind doesn’t always blow the same the entire span of the range. Especially in the West, it’s plenty common to see faster or slower velocity areas between the firing line and the targets. Trees, ground clutter, topography, and so on, all create either passages or obstructions to the flow of the wind. Up to 600 yards, wind nearer the shooter should be given more weight; beyond that distance, wind strength nearer the targets is likely to exert disproportionate influence on the bullet. Reason is a matter of bullet velocity at the point of more or less wind impact. To be clear: even if we’re seeing relatively calm conditions at, say 500 yards, but it’s a tad amount gusty up close to the muzzle, early deflection of the bullet compounds to exert a stronger influence the farther the bullet travels.

range wind speed
Wind doesn’t always blow the same across the full depth and breadth of the range. Up to 500-600 yards, give a little more weight to the wind behavior (speed mostly) nearer the firing line. And, keep in mind that you’re shooting down a one-target-width corridor! Pay attention where it matters.

2. Determine Direction
This should be easy. However! Direction can change just as can speed. It’s not normally going to swap, but rather will vary in fractional shifts. A ticklish wind is a “fishtail” that waffles between 11 and 1 o’clock.

range flag
If there are flags on your shooting range, they mostly function to indicate wind direction, but can be a clue to wind speed: divide the angle by 4 and get an approximation of speed in miles per hour. Call this one 18 mph.

3. Find The Pattern
This may be the most important advice I can give on wind shooting. Wind cycles. Rarely does it blow at a constant and steady rate for very long. Wind cycles every 5-10 minutes. It builds, then peaks, then drops, then as implied, it runs the cycle again. That doesn’t necessarily mean it goes from calm to windy; it goes from windy to windier. But it will change, and most often will do so predictably. Watch the wind for a spell, running a stopwatch, and make notes on what you’re estimating for values at the high and low in the cycle.

At a tournament I want to shoot into a build-up, or, in other words, start my string at the low point in the cycle. And I also want to shoot all my rounds within the timeframe of the cycle! We have 20 minutes at the 600-yard-line, so scheduling can be an important part of strategy for this yard-line.

wind cycle
The most important thing I can tell you about wind: It cycles! Pay attention before you shoot and time the highs and lows you see. Chances are this pattern will repeat over and over at least for the next hour or so. This knowledge is also a huge help to varmint hunters.

If you know what amount a 10-mile-per-hour crosswind will (is supposed to) move your bullet at some distance, interpret the initial correction from that. If you guess the wind at 5 mph, take half of it; if the angle is less than full-value, reduce the correction as discussed last time by the fractional value, like half of the estimated amount for a wind that’s moving from 4:30 to 10:30.

clock face
For reference…

None of this is finite. Reading wind is more art than science. Next time I’ll talk about how to put all the inputs to use and keep all your shots on target.


Information in this article was adapted from material in several books published by Glen Zediker and Zediker Publishing. Glen is a card-carrying NRA High Master and earned that classification in NRA High Power Rifle using an AR15 Service Rifle. For more information and articles available for download visit ZedikerPubllishing.com

Shooting Skills: Shooting the Breeze

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Longer-range rifle shooting isn’t easy, and it’s more difficult when the wind is blowing. Here’s a head start on learning to determine and correct for environmental conditions.


Glen D. Zediker


When I very first started up working with Midsouth, I had quite a few folks writing and requesting to learn more about shooting, and, specifically, NRA High Power Rifle competition. It did my heart good to learn that these folks knew my name and associated it with that venue. HPR has been the main focus of my shooting career. That background is the reason I began the “Shooting Skills” portion of the newsletter, and for a few installments upcoming I will oblige to further go a little deeper.

Wind.

That’s one of the first things that comes to anyone’s mind when High Power is the topic. Describe the tournament course of fire and when you get to “…then 20 rounds at 600 yards…” that one creates a tad amount of anxiety in the imagination.

600 yard shooting
t’s a big, wide, windy world out there. There are several influential factors beyond wind speed and direction, and this series will piece them all together to provide a picture of how to anticipate wind effect on your bullet.

First comment is almost always, “How do you shoot that far with iron sights?” And that’s easy: the target is huge! The aiming black or bullseye is scaled up to a diameter that provides a clear reference to position the sight. And then the next is, “What about the wind…” Well. First, it’s really not that difficult. Second, it’s also really not that easy. You need to know a few things, so here’s where we’ll start.

To be sure, organized competition is not the only venue where learning to shoot in the wind helps. It’s a skill that anyone who fires across more than 200 yards worth of real estate needs to develop. It’s a little easier in a shooting contest because there’s some feedback to work with: holes in the target.

There are two influential components to wind, and, “influential” means the effect on moving the bullet. Speed + Direction. There are good ballistic programs and apps now that provide approximate values: input the points (bullet ballistic coefficient and wind speed) and get a fast answer. That answer is liable to be incomplete, and by that I mean it’s rare indeed to dial in the given solution and hit the target. One at a time we’ll look at other factors which, taken all together, will get you a whole lot closer on that first shot.

The better apps allow also for angular extrapolation, and that is important. Otherwise, if you’re looking at a table the drift amount will be for a “full-value” wind, which is blowing at a right angle or perpendicular to the rifle barrel. Straight crosswind, 9-o’clock to 3-o’clock, or vice versa. If there’s an angle involved, reduce the amount of anticipated drift based directly on the angle: if the wind is angling from, say, 8-o’clock to 2-o’clock we’d say that was a “half value.” From 7-o’clock to 1-o’clock that’s closer to a “quarter value.” So if the drift table says 12 inches, half is 6 and a quarter is 3. At 600 yards it doesn’t really matter if the wind is coming in or going out: head- or tail-winds have little unique influence on the bullet.

And speaking of, there is a different set of “rules” for 1000 yards and more, or maybe I should say different applications or emphases. The reason is because the bullet has slowed down that much more.

At minimum you’ll need to know the advertised BC or ballistic coefficient of your bullet and its muzzle velocity. I wish I didn’t have to continually offer up all the “maybes” and qualifications, but I do because they exist. The actual realized or demonstrated BC of any bullet varies day to day, often during the day. Velocites can also change a bit for varied reasons. However! None of this honestly really matters to the score and that is because the combination of BC and velocity just gets us “close” and finds a place to start from. Ballistics is a finite science, but there are no finite results. With experience you’ll see that BC is really mostly a way to compare different bullets; its value in making truly accurate and finite corrections is limited.

David Tubb 115 RBT 6mm
High-BC profiles are a big bonus, but there’s no magic bullet. The reason better bullets are better is not because there will be less correction on the sight. That doesn’t really matter all that much. Why they are better is because they are less affected by an immediate and perhaps unforeseen change in the wind stats. They are deflected less by, say, a 1 mile-per-hour shift. Shown is a 115 RBT 6mm developed by David Tubb. It’s slick…

All this is affected by air density and that’s a whole other topic for a whole other time. And there’s another list of inputs that each have an influence, and that, again, is why this little series is a series.

Dang. There’s a lot to talk about and I’m pretty much out of space. That’s what “next times” are for. I’ll keep this going long enough to provide some genuine help.

Understand that arriving at a sight solution that keeps the shots in the center involves more input that any “drift/drop” equation can provide.


Information in this article was adapted from material in several books published by Zediker Publishing. Glen Zediker has worked professionally with some of the greatest shooters on the planet, and he does pretty well on his own: Glen is a card-carrying NRA High Master and earned that classification in NRA High Power Rifle using an AR15 Service Rifle. For more information, please check ZedikerPublishing.com