SPEED READER

Air Gun­ner reader Peter Yeats re­searches just how the wind af­fects our pel­lets

Air Gunner - - Contents -

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.

GREATER CON­FI­DENCE

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.

LIM­IT­ING FAC­TOR

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

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