Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
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Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
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Topic: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels? (Read 852 times))
rsterne
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Bob and Lloyd
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
«
Reply #20 on:
September 22, 2021, 07:52:04 PM »
I have asked Miles about the idea of initial yaw affecting the BC, and his conclusion is that initial yaw is related to group size, so for any gun shooting good enough to not hit the Chronograph probably isn't showing enough yaw to affect the BC.... Another reason must be found....
Bob
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1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
mobilehomer
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
«
Reply #21 on:
September 22, 2021, 08:52:50 PM »
From Wikipedia Magnus Effect
In external ballistics
The Magnus effect can also be found in advanced external ballistics. First, a spinning bullet in flight is often subject to a crosswind, which can be simplified as blowing from either the left or the right. In addition to this, even in completely calm air a bullet experiences a small sideways wind component due to its yawing motion. This yawing motion along the bullet's flight path means that the nose of the bullet points in a slightly different direction from the direction the bullet travels. In other words, the bullet "skids" sideways at any given moment, and thus experiences a small sideways wind component in addition to any crosswind component.[24]
The combined sideways wind component of these two effects causes a Magnus force to act on the bullet, which is perpendicular both to the direction the bullet is pointing and the combined sideways wind. In a very simple case where we ignore various complicating factors, the Magnus force from the crosswind would cause an upward or downward force to act on the spinning bullet (depending on the left or right wind and rotation), causing deflection of the bullet's flight path up or down, thus influencing the point of impact.
Overall, the effect of the Magnus force on a bullet's flight path itself is usually insignificant compared to other forces such as aerodynamic drag. However, it greatly affects the bullet's stability, which in turn affects the amount of drag, how the bullet behaves upon impact, and many other factors. The stability of the bullet is affected, because the Magnus effect acts on the bullet's centre of pressure instead of its centre of gravity.[25] This means that it affects the yaw angle of the bullet; it tends to twist the bullet along its flight path, either towards the axis of flight (decreasing the yaw thus stabilising the bullet) or away from the axis of flight (increasing the yaw thus destabilising the bullet). The critical factor is the location of the centre of pressure, which depends on the flowfield structure, which in turn depends mainly on the bullet's speed (supersonic or subsonic), but also the shape, air density and surface features. If the centre of pressure is ahead of the centre of gravity, the effect is destabilizing; if the centre of pressure is behind the centre of gravity, the effect is stabilising.[26]
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
«
Reply #22 on:
September 22, 2021, 10:31:37 PM »
Percentage changes are often used for emphasis. 20% sounds significant. However, if wind drift increased from 0.1" to 0.12", then I question measurement accuracy and the noise normally present in group size. (I assume the drift was larger than this, but don't recall absolute values. Not providing that would be a mistake)
If we are talking 1" VS 1.2" wind drift with different barrels, then that is more like it, but still not conclusive. The way to show what is going on would be to shoot at a longer distance. If that increases wind drift to 2" and 2.4", then the 20% observation would seem to have merit. Else, something else is going on...
If the absolute numbers are small, then even large percentage changes are probably not very meaningful...
In any event, if you want to test the effect of one barrel VS another, you should swap out barrels on the same system. Certainly, the same projectiles should have the same muzzle velocity ideally, or within 5% if possible. If muzzle velocities are different by over 10 % then what is being compared may not just be the effect of the rifling style.
What else is different between the systems? Rifling style and velocity. What about twist rate? The faster the effective twist rate, the greater the aerodynamic jump.
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rsterne
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
«
Reply #23 on:
September 22, 2021, 11:44:12 PM »
Wiki is not always correct.... There is a Magnus effect with regards to bullets, but it does not account for vertical deflection in a crosswind.... It does affect bullet stability, however.... If you want an excellent resource on bullet stability, I suggest this one....
http://ffden-2.phys.uaf.edu/212fall2001_Web_projects/Isaac%20Rowland/Ballistics/Bulletflight/index.htm#Contents
I mentioned before that velocity, twist rate, etc.etc. would have to be the same for the 20% to mean anything.... Also, you are correct, if the drift is not larger than the average group size, then 20% means nothing.... as it would be overwhelmed by the (in)accuracy of the testing....
Bob
«
Last Edit: September 22, 2021, 11:50:09 PM by rsterne
»
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Coalmont, BC, Canada
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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
«
Reply #24 on:
September 26, 2021, 11:49:35 AM »
Subscriber and Bob, great thread here. Nothing to add other than following.
Psst I go LW and have great accuracy with them.
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Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?