Wind - Near or Far?

One of the questions which comes up occasionally on internet boards and which can cause a bit of consternation is whether greater allowance should be made for wind conditions nearer the shooter or nearer the target. A surprising number of people believe that the wind nearer the target will have a greater effect, after all the bullet is going much more slowly when it gets to the other end.

Let's look the ballistics of a shot fired by a target rifle shooter on a flat, open range with a 10 mile per hour crosswind from 3 o'clock. (S)he is using ammunition with an old-style Sierra 155 HPBT bullet (part number 2155) with an average real-world BC of 0.417 (vid. Brian Litz's superb experimental data) which achieves a muzzle velocity of 2925fps*. Using the JBM Ballistics page, we get the following results:

Range	Muzzle	100x	200x	300x	400x	500x	600x	700x	800x	900x	1000x
Velocity / fps	2925	2711	2505	2306	2117	1937	1764	1596	1443	1307	1193
Wind Drift / Inches	0	0.7	2.9	6.8	12.7	20.7	31.2	44.6	61.4	81.8	106.1
Time Elapsed / s	0	0.107	0.222	0.347	0.482	0.630	0.793	0.972	1.169	1.388	1.629

EDIT: The tables in the figures are now correct! I transposed the times of flight from the 1307fps muzzle velocity calculation onto the data for the 2925fps calculation.

We see that the last 300 yards account for more than 50% of the wind difference. Clearly the wind closer to the target is more important, right?

Not so fast!

I was taught that the wind closer to the shooter has a greater importance, and the various books I've read tend to agree on this point. My experience on most rifle ranges tends to agree; although there are notable exceptions. Let's perform a thought experiment:

Scenario 1 - The same shooter fires a shot on the same flat, open range at a target 1000 yards away. For the first 900 yards, the air is perfectly still. In the final 100 yards, there is a 10mph/16kph wind running at 90 degrees to the line of flight. We know that the wind drift will be zero for the first 900 yards; however we need to calculate what the drift will be in the final 100 yards, which we can do using the ballistic calculator. Using the results from the JBM ballistics page the bullet will be going about 1307fps at 900 yards. Re-entering this value as the muzzle velocity allows us to calculate what the wind will be over the final 100 yards of the range.

Range	Muzzle	100x
Velocity	1307	1193
Wind Drift / Inches	0	1.9

This gives us a total effect of about 1.9 inch or 0.2MOA from the perspective of the shooter 1000 yards away, which is roughly equivalent to the contribution of the final 100 yards to our hypothetical shooter's first shot; therefore the wind in the last 100 yards accounts for only 2% of the total deviation.

It would be interesting to know, by way of contrast, how much wind the first 100 yards would account for. To understand this, let us return to our hypothetical shooter:

Scenario 2 - Our shooter fires another shot at a target 1000 yards away; however this time for the first 100 yards, there is a 10mph/16kph wind running at 90 degrees to the line of flight. In the remaining 900 yards, the air is perfectly still. What will the deflection of the bullet be? We know from our original calculation that the bullet will have drifted about 0.7 inches in the first hundred yards.

This is where is gets interesting. Even though there is no longer any wind, the bullet will continue to move sideways even as it flies downrange because of Newton's 1st Law of Motion**. Thanks once again to Sir Isaac, we can estimate the sideways velocity of the bullet as it transitions from the windy 100 yards into the remaining, still 900 yards; and therefore the total deviation.

If we calculate the acceleration on the bullet over the first 100 yards given the known displacement and time of flight, we can then calculate its sideways velocity at the end of the 100 yards. The bullet will continue to travel sideways at this velocity as it flies down the range, but no faster because there is no more wind.

Following a series of calculations, I make this about 20.6 inches*** however because of errors in assumptions this could be as much as twice the actual contribution. Even so, it is between 5 and 10 times the effect of the wind nearest the target.

Conclusion
Hopefully I've provided a reasonable argument that as a general rule, the wind nearer the muzzle has a greater effect than the wind nearer the target on a flat, open range; however ranges are not always (often?) flat or open in the real world!

Clevedon rifle range is situated just outside Auckland, lies between a series of low hills, and points towards a ridge with several deep ravines leading down to the butts. Particularly at 600 yards, the flags closer to the butts appear to have a greater effect than the ones closest to the firing point. While it is entirely possible that we are mistaken in this; I and other club members think that the funneling effect from the ravines coupled with the shelter of the hills alongside the range leads to this rather odd observation.

The 500x point on Clevedon rifle range near Auckland. Not flat or open!

Indeed, most ranges have their own quirks which must be learned: it is for this reason that top-level teams frequently send advance parties to recce ranges the year before major championships, the Palma Match in particular. I have no doubt that GB, the US and other teams will be sending shooters and coaches to New Zealand to learn the inimitable character of the mighty, frustrating and rewarding Trentham Rifle range.

* This is roughly equivalent to RUAG or GGG.
** A body will remain in constant motion unless an unbalanced force acts on that body.
*** Actually, it will be a bit less because of wind resistance but this is going to be reasonably close.

Addendum - Scenario 2 Calculations
To calculate the acceleration due to the wind on the bullet, let's use one of Newton's equations of motion...

s = ut + 1/2 at^2

Where:

• s = sideways displacement of 0.7 inches
• u = initial sideways velocity of 0 (the bullet isn't moving sideways when it exits the bore)
• a = acceleration that we want to calculate
• t = time elapsed of 0.107s

s = 1/2 a t^2

2s = at^2

a = 2s / t^2

a = 2 * 0.7 / 0.107^2

a =  122.1 inches per second ^ 2

Using this acceleration and the time of flight for the first 100 yards, we can calculate the sideways velocity of the bullet at the end of the 100 yards.

v = at

Where:

• a = Acceleration of 122.1 inches per second ^ 2
•  t = 0.107 seconds

v = 13.1 inches per second

We can calculate the total wind drift by adding to the 0.7 inches of drift in the first hundred yards the sideways drift over the next 900 resulting from this velocity.

s = 0.7 + 5.8 x (3.158 - 0.241)

s = 20.6 inches

NB - There are two limitations that I can think of to this: Firstly, this discounts wind resistance; and secondly, the acceleration on the bullet will reduce as it approaches the wind velocity. Both of these will tend to over-estimate the effect. By applying a similar calculation to the whole 1000 yard range it is possible to see that the over-estimate is at worst 100%.

Trials and Tribulations

The process of actually getting to go to the Commonwealth Games is a long and often frustrating one; even after you have notionally been selected by your NGB*, there may be a whole host of other criteria to be fulfilled and indeed as one person once put it to me: you're not 100% sure until you're sitting on the plane waiting to take off. You need to convince them that you're capable of a medal-winning performance on the day.

I cannot speak for the other countries involved in The Games, whose selection processes may involve anonymous committees in smoke-filled rooms and the reading of entrails following the ritual sacrifice of small animals for all I know**; however Team Wales, the WTSF and the WRA jointly have a fairly straightforward approach, which can be summarised from the point of view of an athlete thus:

1. Do lashings and lashings of individual and pairs training
2. Come in the top 2 in the nominated ranking events
3. Shoot as many minimum consideration scores as humanly possible, preferably during competitions involving other CWG-level athletes, whom you beat during the process

There is considerably more to the formal procedure than this from the point of the NGB, but this gets to the heart of what you actually need to do and can control in order to get selected. My legendary pardner CJW and I have achieved #2, have solid plans in place for #1, and are both working on #3. Unfortunately #3 involves shooting a total of 399 out of 405 for a full HM Queen's Prize course of fire, which is no mean feat; doubly so when you live in a country where no one ever shoots a full HMQPCOF. Fortunately, I also live in a country of fine, upstanding people who are willing to muck in and help out a fellow rifle shooter in need; and, to cut a long story short, I've been shooting alongside the NZ CWG ranking events which do involve shooting the full course of fire.

Fast forward to last week, when I got to spend a wonderful four days down at Trentham trying to shoot an MCS while simultaneously not cocking up anyone else's shoot. At this point enormous thanks are due to a moderate-sized cast of people who helped out by ROing, butt marking, logistics etc... etc... So 'nuff respect*** to Kevin Win, Tony Gore, Andre Doyle, Vic and Jared McMurdo of HotloadeD Kiwi fame, Eben Fourie, Darryl Crow, John McLaren, Brian Carter, John Snowden, Bevan Mehrtens, Malcolm Dodson, John Whiteman, Geoff Smith, Rob Johansen, Rick Fincham, Allen Owens, Henry Firmston, and all the others who helped out and made things run super-smoothly.

The downside is that I didn't get an MCS; I managed two 396s. Boo! The upside is that I did have some excellent groups and only one dodgy shoot. Yay!

35.6 at 300x in Trial 2

35.7 at 500x in Trial 1. Bring it.

35.6 at 600x in Trial 1. Tough to get on 600x ICFRA targets.

On the other hand, the second of my 396s would have been a 401 (and therefore a minimum consideration score by 2 clear points) had I not carelessly placed one of my shots on an adjacent target at 900 yards. Boo!

Shot #12 rather spoiled the look of the thing.

While I didn't ultimately get the result that I wanted out of the weekend, it was a really worthwhile exercise now that I have some emotional distance on the crossed shot: I got to shoot two full courses of fire with top flight shooters; had some great results; have confirmed that my brand new jacket does not fit; have confirmed that the tweaks I have made to my old jacket have helped; and it is clear to me that I can (still) shoot the groups and scores required. Roll on June, when I'll hopefully get a chance to shoot a full course of fire on Belmont Range in Australia, the 2018 Gold Coast CWG venue.

* National Governing Body. It actually may not be entire clear who your NGB is, or indeed there may be more than one body you need to satisfy during the process.
** You know who you are.
*** I may be up to date on shooting terminology, but my chat dates from the mid-90's.

The Trouble with Jackets

If there is one bit of kit which seems to present more problems than any other, and certainly the one about which I get the most questions, it is that of shooting jackets. Other things seems to be much more of a science: rifles are pretty well understood*; spotting scopes themselves are fairly easy, and positioning a mere matter of trial and error; mats ditto; hats a personal preference but still fairly hard to get wrong; gloves ditto. By way of contrast, nothing but nothing seems to be so perversely difficult to get right as obtaining and maintaining a properly-fitting jacket. Unfortunately, this is one area where I definitely do not have all of the answers.

My personal bugbear in this regard is that I appear simply to require that I get a new custom-fitted jacket made every two to three years, or at the very least have my existing jacket retailored. This is expensive and a logistical pain in the arse. I have mentioned problems I have had with jackets in other posts but that was really the result of a one-off change in my body shape; what I'm really referring to in this post is what I shall term jacket fatigue.

Understanding that you need a new jacket or that your existing jacket needs a spruce up is only the start! Tales abound of recut jackets fitting even worse, and the sheer worry of sending off your order to Switzerland or Finland with the best part of 500 quid spent only to get something entirely unusable back drives many to despair. Believe it; it happens.

Why, Dear God, why is it so hard?

Shooting jackets must fit well across the shoulders and the backs of the arms to allow proper position and relaxation of the supporting arm as well as consistent positioning of the sling. Tension in this arm, or a sling which gradually slides down, pulling the jacket with it, is not a recipe for top notch accuracy. Even if you are able to maintain a good hold and release for individual shots, the shifting position will also shift your natural point of aim, which is very likely also to shift your point of impact.

Shot with a jacket which allowed the sling to slip. Each individual shot is good, with low trace and release numbers but the overall group is shoddy because of inconsistent NPA.

Firstly, jackets wear and stretch over time: Even the best materials are slowly distorted by the forces imposed on them during shooting. Secondly, our bodies also change in shape over time**. I have both lost and subsequently redistributed weight, but others will gain it or will change shape in other ways because of exercise, injury, illness or the aging process.

Possibly more than this, at least in fullbore where serious coaching may be a rare commodity, shooters don't always know as much as they might about how it is that jackets actually fit and commit a variety of misdeeds. I've certainly been guilty of this in the past and one of the only upsides to having to go get refitted every so often is that I learn more each time. Chief among these crimes is the idea that the jacket should fit as tightly as possible, most particularly in the padded shoulder, whose straps are cinched to twanging point. While this is an occasionally-useful hack to make an oversize jacket work, it is not really a sustainable solution and can result in further stretching and distortion.

Note the straps in the right shoulder have taken up the slack, but aren't so tight as to completely distort the fit of the jacket.

While I'm hesitant to give hard recommendations on this issue because I seem to have so many issues with it personally and I'm not going to recommend a particular brand or style of jacket because all of them can be made to work if they fit appropriately, a few of the lessons I have learned are:

When buying a new jacket...

1. Take the time to get jacket fitting right - Jackets are very expensive and even more so when they don't work because of time taken to get them sorted, wasted training hours etc...

2. Don't necessarily expect it to fit perfectly first time - I have been fairly lucky in this regard so far**, as only 1 of the jackets I ever had just outright didn't fit. It was still an expensive experiment and wasted a year of my time before I got it sorted. Friends, particularly females, have sometimes had serious issues in getting jackets fitted correctly. This seems to be more of an issue in ladies with an impressive decolletage.

3. Think about a local supplier who can make alterations - When #2 is an issue, you're going to need to get it recut. If at all possible, find someone local to fit it to you who can make minor tweaks to the fit as this will save a long lead time if your jacket is made abroad. I recognise that this may not always be possible.

4. Consider whether your existing jacket just needs a refit - Sometimes there's nothing really wrong with the old jacket that some new pads and a bit of a recut won't sort out. Many shooters out there run with the same jacket for many, many years before needing a new one. (Just not me, apparently.)

5. Do not get rid of your old jacket - A well-known shooter and former world champion of my personal acquaintance got a new jacket (supposedly an upgrade) and proceeded to have a miserable season; however because he still had his old jacket available, he was able to swap back and saw his scores climb back up to what they had been previously.

6. Buy your jacket at the end of the season so you have the winter to get used to it and have time to sort out any logistical cockups. Ordering a new jacket to arrive the week before the Nationals is not a risk-free exercise.

More generally...

7. Jacket fit is driven by bodyweight and body shape. Most of you will change in your body weight but relatively little in shape once you're in your twenties; however be aware that major changes in lifestyle can effectively change your bodyshape semi-permanently***.

8. The jacket doesn't need to be as tight as you can possibly fit into; it should be snug but allow you to breathe. The fit across the shoulders is more important.

9. Do NOT have the straps in the right shoulder as tight as they will go because this will tend to loosen the jacket in the opposite shoulder.

10. If you find your SCATT tracelengths increasing, or if you find you have to adjust your position during a shoot with your groups enlarging as a result then your jacket may be coming out of fit.

In summary, buying a jacket can be expensive, difficult and time-consuming. My suggestions above do not in any way guarantee success because jacket fit is an art not a science; however I'm hoping that they may reduce the frustration a little.

* Although I admit that stock fit can sometimes present a few issues.

** Hold this thought, I'm in the process of having a new Kurt Thune Prone 600 jacket made at the moment. Review to follow.

*** Try going from no significant exercise in over a decade to running 60+ miles per week. That ought to do it.