Is faster always better in the wind? New slug info page3

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About point #2

I always say that SOME of us need more than 20-24x. If I can't see it, I can't hit it. These old eyes just ain't what they used to be. I put a 10-50x60 and usually shoot at the lowest X that allows me to see what I'm shooting. Usually between 24 and 30. But the 50 is handy at 100 to see where a stray pellet hit :)

@CampFussell

Amen Crusher, that's what I like as well. A 10-50x60 Sightron on 30 power works perfect for me at 100 yds. I can usually see where the pellets hit even on 30 power. 24 power would be my absolute minimum for those long shots at the 100 mark
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I hear both of you, however... I have a word for you - GLASSES! Now, I know they are something new and experimental, but they actually improve your vision... ;)
 
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So why does the projectile drift? Obvious answer would be. Because the wind is pushing on it. However it could be the air mass the projectile is in is moving and just carrying the projectile along with it, a combination of the two or something else. I think nature prefers to push things over pulling them. Like gravity doesn't pull things down from below but actually pushed them down from above.
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I am not an expert, but I believe with pellets that make sence. Pellets are incased in a "bubble" with turbulant air surrounding them as they travel downrange. The faster the pellet moves, the bigger that bubble will get. So if we think of that bubble surrounding the pellet acting as a sail, for the wind pushing it out of course, it is probably benefitial to have a smaller bubble with more moderate speed.
 
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Thanks @hoople. Very interesting that the sweet spot for slugs is in the 900 to 950 FPS range, and wind performance actually decreases significantly above 1000 FPS. 

Below, from the Hard Air Magazine article referring to slugs with a BC of 0.1, which seems to be about ballpark for most of our Airgun slugs.

{Note that the least wind drift occurs when starting with a muzzle velocity of about 900 fps, and increases when the MV is either slower or faster. This chart is quite a shock to most slug shooters. It shows an increase in drift of about 10% by increasing the MV from 1000 fps to 1100, and an even greater increase above that. Combined with how much more air it takes to reach 1100 fps, if shows that even for slugs there is little point striving for much over 1000 fps.}
 
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Did you guys & gals not read up on the math at the link provided for Didion's equation?

It's pretty clear, wind deflection is proportional to the time of flight.

The summary quote is "While equation (6) is not intuitive, it clearly shows the Deflection behaves to Muzzle velocity inversely proportional."



I also believe that for PELLETS, when velocity approaches Mach, stability suffers and groups open up.
 
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Ahhh, a conceptual error... wind drift is proportional to the differential time of the pellet in a vacuum, and the pellet in actual flight. It has nothing to do with actual flight time. Differential flight time is directly proportional to the BC of the pellet at that speed. This is why wind will affect a standard 18.1 grain pellet (or any other diabolo pellet really) more at 1000 FPS than at 900 FPS because the BC starts dropping at around 950 or so FPS. Yes, very counterintuitive, but science is science backed up by real world testing...
 
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"Ahhh, a conceptual error… wind drift is proportional to the differential time of the pellet in a vacuum, and the pellet in actual flight" Bzzzt, sorry, wrong.



The SPEED of the pellet will reduce the differential time so the duration of effect is lessened.

Note the quote again "Deflection behaves to Muzzle velocity inversely proportional."- no differential time in that quote -- all about VELOCITY.



Ignoring SPIN - just using basic kinematics of time, force and distance.

If you travel 100m in 1 second you have 1 second of side force which will push you some amount of distance sideways.

If you travel the same 100m in 0.5 seconds, you have 0.5 seconds of exposure to THE SAME side force.

Why would half the duration of THE SAME side force yield MORE movement? It won't. It can't. 




 
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Not going to argue. You’re reading it wrong, and making assumptions based on perceived logic, and not Physics. Sorry. Do me a favor. Go into Strelok or Chairgun. Choose 50 yard zero and 100 yard range. Then input a pellet, say .25 Kings with BC of .042. Now choose 10 mph wind drift at 90 degrees. Pellet speed 900 FPS. It will show wind drift at 100 yards in inches, Mil or MOA. Now change nothing else and make the 900 into 1050 or even 1000 FPS. Now look at what happened to total wind drift. It got LARGER. Funny how the math backs up the facts. Actually, I truly hope it’s windier than normal at EBR, and the Daystate Team are all shooting their .25 Safaris at 1070 FPS. Gives all of us shooting at 900 to 950 an advantage...

;)
 
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Ahhh, a conceptual error... wind drift is proportional to the differential time of the pellet in a vacuum, and the pellet in actual flight. It has nothing to do with actual flight time. Differential flight time is directly proportional to the BC of the pellet at that speed. This is why wind will affect a standard 18.1 grain pellet (or any other diabolo pellet really) more at 1000 FPS than at 900 FPS because the BC starts dropping at around 950 or so FPS. Yes, very counterintuitive, but science is science backed up by real world testing...
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Yep, all about the delta vacuum. Better bc wins every time. Don’t believe us? go ahead and punch the numbers in a good ballistics calc.
 
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Bingo! +1 to you... It’s such a difficult concept that some shooters would rather try and “logic” their way into the “faster is better”. I even posted the derivation of the calculus required to prove the actual observed data. Yep, Earth is flat, Moon is made of cheese, the Sun revolves around the Earth, and Electrons are the smallest particles...

;)
 
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Pretty plain and simple here's some calculations straight from Chairgun

1564202318_17294225345d3bd54ebb9321.08768088_Screenshot_20190726-213634.png


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I love to shoot long range with PCPs, but I live in a region that is plagued with lots of wind for most of the year. I read into Bob Sterne's velocity and wind drift threads a little while back, and what he says on paper is pretty accurate.

That said, I have found that there's a lot more to a projectiles performance in the wind. The form factor and cross section plays a huge role in that (as do the rifle and barrel).

An important thing that I have come to accept, is that every projectile is going to have a maximum velocity that sits on the edge of the drag coefficient "curve", before it begins to drift exponentially. I have seen this to be as dynamic as:

  • 910fps with .217 shooting 24gr (BC of 0.11 muzzle > 100m)
  • 930fps with 50gr / .300 (BC 0.08)
  • 870fps with 34gr / .250 (BC 0.07)
  • 990fps with 28gr / .217 (BC 0.094)

Every one of those rifles were sub-MOA shooters in calm/light winds. I had tested every one of them extensively to find their maximum velocities that they could be tuned for to shoot the tightest groups possible in the wind.

The science of external ballistics is fascinating, and one that has more parameters and variables than most of us (or anyone) could record shooting outdoors. I realize this, and while I'm trying to soak up all that I can in this realm - results are far more practical towards shooting accurately, and having fun. Read less, shoot more ;-)
 
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MtnGhost- Best piece of advice yet! READ LESS,SHOOT MORE!
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Great info!

What's also interesting is look at how much faster the higher speeds sheds there fps proving the BC suffers in that transonic zone. Starting off with a 150fps "head start" it's down to only 60fps by the time it reaches 100yds. At only 900fps the fps loss is 290fps while at 1050fps the fps loss is 380fps.
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These two posts sum it up totally IMO. The trans-sonic zone crossing seems to be the critical point in the issue. And one should shoot more in the wind to learn how your gun and projectile work.
 
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