Air Gunner reader Peter Yeats researches just how the wind affects our pellets
Air Gunner reader, Peter Yeats, shares his findings on how wind speed affects pellets
Dear Phill, Your comments on longrange hunting prompted me to write to you on this subject. I offer this information to illustrate my support for your views, and my new appreciation of just how little wind it takes to change a pellet’s POI ( Point Of Impact) dramatically. I fully endorse your comments about excessive range, because windage is an unpredictable variable and stable shooting from a bipod isn’t always available. Your comments prompted me to think more deeply about how a hunter, using a PCP, laser rangefinder and bipod, could make more precise assessments of windage, improving accuracy and understanding how gusts of wind MUST limit range significantly. If the difference between highest and lowest gusts lead to a windage variation of more than half the size of your target zone, then it doesn’t matter how brilliant you or your equipment are – you can’t be certain of hitting the kill zone and the shot can’t be taken humanely.
So, how can a shooter calculate/ estimate the windage as accurately as possible? The first realisation was that my estimation of wind speed is exactly that – an estimation, and little more than an educated guess. Following this conclusion, I used Hawke Chairgun software to calculate windage for various distances and wind speeds, to produce a quick reference graph to carry in the field. This shows that had there been only a 3kph side wind for a successful long shot at 65 yards, the required aiming point would have moved about 4cms, and I’d have missed the shot. I don’t know anyone who can estimate windage with a resolution of 3kph/2mph, so accuracy in knowing wind speed is critical, even to relatively short- range hunting shots. My next step was to purchase a pocket anemometer to measure wind speed, and then to compare its readings to all the other environmental indicators, before deciding on whether or not a shot should be taken. The last part of my calculations was to prepare a table showing windage for my scope, at my preferred magnifications of x6 and x12, in mils and half- mils, at various distances. These I also combined in my graph.
I have checked this out at my permission at 55 metres, and with a crosswind of 8kph; windage was 9cm or one mil- dot at x6 magnification; the target was a red onion about 4cms in diameter; my gun was rested and I fired eight shots. The aiming point was exactly the same for all eight shots; six were hits and two missed. The maths clearly are accurate and with more practice I know I’ll be able to shoot with greater accuracy and confidence in correcting for windage. Will this greater accuracy mean greater range in hunting? Definitely not. It will mean greater confidence out to 40 metres, that’s all.
These calculations are for my kit alone; a .22, running at 11.4 ft.lbs, shooting RWS Superfield (15.9grains, 0.031BC). I hope that the maths, the graph and explanations show that even doing all you can to adjust for windage,
with any significant wind speed, the margins for error beyond 40 metres mean that one- shot accuracy drops away very quickly indeed, ending any real certainty of humane long- range hunting. At distance, very small variations in wind speed greatly change point of impact.
The greatest limiting factor in longrange accuracy is windage, and that’s not a black art; it’s science. What science shows is that if there is the SLIGHTEST variation of wind from the assessment for the shot, beyond 45 metres the shot will miss the kill zone.
I believe I have looked at this issue objectively and carefully, to conclude that you are correct; it is not possible to take humane shots consistently at over 40 metres, at live quarry, in real- world hunting conditions, no matter how carefully you prepare for the shot.
Best regards, P. YEATS.
The editor responds:
I’m delighted that Peter went out and tested his equipment and theories in the real world so that he could see for himself exactly what goes on as our pellets fly down range. It’s clear to me that he applied himself very seriously to the challenge and has thought deeply about the subject. I disagree with him on just one point, and that is the size of his target. I think that a 4cm onion is too large because a rabbit’s brain is nearer 2cm, and a hit outside that vital area would wound and not kill cleanly. Having discussed this with Peter, he says that he agrees with my thinking on this, and it presents the question – of the six hits he observed from his eight shots in his test, how many more would have been misses on a 2cm target? It’s all well and good reading about a subject, but there’s no substitute for running tests yourself with your own rifle. In this way, you can be confident that what you’ve read is right – or deserves to be challenged, which is also important. By pooling all the knowledge and experience we have as an airgun shooting community, we can continue to learn and improve the sport.
ABOVE: Reader, Peter Yeats did the testing himself to find the real facts
LEFT: 4cm is too big a target to represent a rabbit’s brain. 2cm is closer
LEFT: Clever reticles are a help but not the answer
FAR LEFT: Your anemometer tells you the wind speed where you are now, not when your pellet is fired