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Author Topic: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?  (Read 439 times))

Offline Gear_Junkie

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Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« on: September 18, 2021, 04:59:19 PM »
I was doing some testing today to see how much the wind affects a pellet fired from a LW poly barrel vs. a traditional rifled barrel.  I've heard that the wind has a noticeably smaller effect and I wanted to test this out to see how much.  I used a flag and a wind meter to measure the wind speed and ensure that the wind was going as close to 90° to the path of travel as possible.  I also did all of my tests at 40 yards, since this is the farthest that I can easily shoot.  I compared my wind drift results with that of Chairgun.  Based on my hoaky test, it looks like the poly barrel may reduce the effects of the wind by about 20%.  I realize that this is only 1 pellet, shot at 1 distance, and basically a pretty hoaky test, so I'm mainly using this as a primer to see what anyone else has found.

Thanks!
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Offline ranchibi

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #1 on: September 18, 2021, 06:25:03 PM »
Zack, very interesting results! Were the pellets going the same speeds? I would think with a choked barrel, the projectile slows down at the choke while a non choked poly barrel wouldn’t (if you are speaking of a non choked poly as there are choked poly’s). Also I would think that the spin would be also be reduced because of this but I’m just guessing and probably making wrong guesses as usual! LOL! All I know is that the non choked poly barrel Martin picked for my .22 RAW is waaayyyy more accurate than I am by far! Anyway, interesting find!
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Offline Bayman

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #2 on: September 18, 2021, 06:42:26 PM »
Can you please explain why a poly barrel changes the effects of wind on a projectile?
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #3 on: September 18, 2021, 07:48:41 PM »
IF (and that's a big if) the drag is less when shot from a Poly barrel, then the wind drift would be less as well, assuming the muzzle velocity is exactly the same.... However, if the MV is different, the drag will be different as well, and depending on what part of the drag curve you are, that velocity change may change the drag and drift as well.... Wind drift is proportional to pellet drag, assuming the weights are identical.... However, a heavier pellet (of the same caliber) with the same drag will have less wind drift....

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Offline Bayman

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #4 on: September 18, 2021, 10:32:09 PM »
IF (and that's a big if) the drag is less when shot from a Poly barrel, then the wind drift would be less as well, assuming the muzzle velocity is exactly the same.... However, if the MV is different, the drag will be different as well, and depending on what part of the drag curve you are, that velocity change may change the drag and drift as well.... Wind drift is proportional to pellet drag, assuming the weights are identical.... However, a heavier pellet (of the same caliber) with the same drag will have less wind drift....

Bob
I don't understand. Once a projectile leaves the barrel isn't the drag or BC dependant on the projectile rather than the barrel it came from?
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #5 on: September 19, 2021, 01:43:26 AM »
Once a projectile leaves the barrel isn't the drag or BC dependant on the projectile rather than the barrel it came from?

If the barrel significantly changes the shape of the pellet, then the barrel can have an influence on projectile drag.


That said, I would like this kind of evaluation to be done "double blind" so there is no human influence on the result.  In this case, timing of the shot during gusty wind, for example. 


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Offline Franklink

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #6 on: September 19, 2021, 03:29:49 AM »
Similar experience here.

Less drift with poly barrel, in the context of field target legal (sub 20fpe) .177.

I did a bunch of comparisons between 12 land&groove LW, poly LW, and cold hammer forged BSA barrel, including pics of pellets pushed through those barrels.
https://www.gatewaytoairguns.org/GTA/index.php?topic=169326.40

Much smoother imparted rifling marks on pellets through the poly barrel. Logic says less edges on the pellet for air molecules to interact with->more "slipperyer" in flight -> less deflection.

Reply #48 in the above link is probably the most conclusive experiment I did on this.
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Offline Franklink

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #7 on: September 19, 2021, 03:33:00 AM »

[/quote]
I don't understand. Once a projectile leaves the barrel isn't the drag or BC dependant on the projectile rather than the barrel it came from?
[/quote]

Yes, but that projectiles flight shape was created by the barrel it passed through, so there's the net effect of the air blast expanding out the skirt (obturation), as well as the rifling marks imparted into the pellet.

I always think about boat propellers when this comes up. Small little trolling motor doesn't have very big or aggressive blades on the propeller. High speed outboard motor has much more aggressive "fins" on the propeller. With pellets, the medium through which it is passing is air instead of water though.
« Last Edit: September 19, 2021, 03:39:23 AM by Franklink »
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #8 on: September 19, 2021, 04:01:13 AM »
Frank,

LW barrels with conventional rifling have groove depths 20 to 50 % greater than typical airguns in .177 and .22 caliber.  I suspect that is why the wind drift for BSA conventional rifling barrel was similar to the Poly barrel:  The BSA barrel's rifling is probably shallower.
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #9 on: September 19, 2021, 04:13:32 AM »
Frank,

There is another reason why the BSA barrel is shooting pellets with a less wind drift:  The effective BC is higher because the pellets have less frontal area.  This is because the nominal caliber of the BSA barrel (or the choke) is a smaller diameter than the other two barrels.  It can be seen by the pellet head engagement with BSA barrel groove diameter - your pictures below.





I couldn't quite get the detail I wanted in the above pics so took the following as well.






(added some arrows here because it's just so hard to see the engravings with the poly)









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Offline Doug Wall

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #10 on: September 21, 2021, 08:51:39 AM »
" I realize that this is only 1 pellet, shot at 1 distance, and basically a pretty hoaky test"
You're right about that. Unless you had a continuous wind profile all the way down range, one shot can't possibly tell you that. Try 20 shots from each type of barrel in the same session (10 of barrel 1, 10 of barrel 2, 10 of barrel 1, 10 of barrel 2), and then get back to us.
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #11 on: September 21, 2021, 08:56:28 AM »
Doug,

I think Zack meant one distance, and one pellet type.  Not just one shot.  At least I hope that is what he meant...

Else, I agree that the test needs to be split back and forth to average out unsteady wind.
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Offline Franklink

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #12 on: September 21, 2021, 10:46:24 AM »
Mine was a comparison of a couple hundred shots. If memory serves, I think I shot 7, 10 shot groups from each type of barrel, rotating through them to gather a cumulative effect of variances in whatever the wind was doing during the test.

Less scientifically, in monthly FT events I went from a 12 l&g LW barrel to the poly and saw that at FT distances (10-55 yards), the poly barrel simply requires less hold-off for wind. Also have compared hold offs to my poly gun and squad mates at ft events and the traditional barrel guys always seem to report having to hold off for wind more than my poly gun, on the same targets.  In that last example we're of course taking our shots 5-10 minutes before or after each other, but I possess no magical wind-controlling abilities to improve conditions for my shots and worsen wind conditions for their shots.
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Offline Gear_Junkie

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #13 on: September 21, 2021, 06:16:42 PM »
Doug,

I think Zack meant one distance, and one pellet type.  Not just one shot.  At least I hope that is what he meant...

Else, I agree that the test needs to be split back and forth to average out unsteady wind.

Yes, you are correct - I should have provided a little better explanation.  I shot about 10 - 20 shots at the 40 yard target.  I would wait until my wind flag showed a fairly consistent 5 mph wind, and would then take a shot.  Frank's testing is MUCH more exhaustive and useful.  Really, I was just hoping to hear what results other people have found using the poly barrels.
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #14 on: September 21, 2021, 09:54:35 PM »
So, here are a few silly questions:

Won't aggressive marks on a projectile cause vertical dispersion in a cross-wind? 

Why would different rifling marks on the projectile cause more or less wind drift, unless the marks somehow change the projectile BC?

I still think that different choke diameters are affecting the effective sectional density and thus the BC more than the rifling style.

I can see shallow/gentle marks on the projectile reducing the vertical dispersion in a cross-wind.

If the different rifling styles have different twist rates, the average projectile yaw could for a given twist could also affect the effective frontal area of each projectile.  Thus their drag.  Thus their effective BC.  Thus their wind drift.
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Offline rsterne

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #15 on: September 22, 2021, 12:17:00 AM »
Rifling marks, or serrations on the skirt, have been suggested to cause vertical dispersion in a crosswind due to the "Magnus effect".... However, this is not possible, as projectiles turn to face into the "apparent/relative wind", which is the vector sum of the forward velocity and the crosswind.... This means that as far as the pellet is concerned, there is no crosswind, so the Magnus effect cannot apply....

Years ago I had this wrong, too.... until I was set straight by British Ballistician Miles Morris.... Reading Reply #35 in this thread will make this crystal clear, along with explaining that drag is the cause of wind drift.... Once the projectile yaws into the wind, a portion of its drag is directed downwind, causing the drift....

https://www.gatewaytoairguns.org/GTA/index.php?topic=169459.35

There is a vertical dispersion in a crosswind due to "aerodynamic jump", which is a gyroscopic reaction to the slug turning into the apparent wind.... but it is not Magnus effect.... The yaw into the crosswind causes a gyroscopic reaction at 90 degrees to that, up or down, depending on wind and twist direction, and whether the CG is ahead or behind the CP.... Pellets react in the opposite direction to bullets for that reason.... Aerodynamic jump causes groups to be sloped (angled across the target) in gusty winds, rather than being strictly horizontal....

Notwithstanding the above, if the pellet has higher drag, it will have greater drift.... Conversely, if the SD is greater (smaller frontal area) it should have less drift.... However, even a 0.004" smaller diameter (in a .22 cal), due to a choke for example, would only increase the SD by 3.6%.... and the drift by a similar amount.... Therefore, if there is indeed 20% less drift, I would suspect a large difference in drag.... Rifling depth and/or smoothness may be the reason, but it still seems like a lot of difference to me.... A significant difference in the initial yaw exiting the muzzle, and how quickly that damps down, so that the pellet isn't wobbling as much.... would seem a more likely suspect for that sizeable extra drag.... A close look at the squareness of the crown (tipping/yawing the pellet on exit) may be in order.... Wobbling projectiles have a lot more drag....

Bob
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #16 on: September 22, 2021, 01:20:40 AM »
Thanks Bob,

If pellet wobble as it emerges from the muzzle is driving the BC down, might one see that as velocity loss in a windless indoor range?  Either measured with a chronograph, or as a lower POI.

If a reduced BC outdoors explains the wind drift when using some barrels, would the pellet drop over range outdoors not also indicate a greater velocity loss?  Perhaps two similar chronographs can be placed at 1 yard and 50 yards to measure a number of shots.  Then the chronographs can be swapped, and the results used to null out chrono calibration.

Of course, it is easy to design burdensome tests for someone else to do :)
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Offline Bayman

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #17 on: September 22, 2021, 08:46:12 AM »
Thanks Bob,

If pellet wobble as it emerges from the muzzle is driving the BC down, might one see that as velocity loss in a windless indoor range?  Either measured with a chronograph, or as a lower POI.

If a reduced BC outdoors explains the wind drift when using some barrels, would the pellet drop over range outdoors not also indicate a greater velocity loss?  Perhaps two similar chronographs can be placed at 1 yard and 50 yards to measure a number of shots.  Then the chronographs can be swapped, and the results used to null out chrono calibration.

Of course, it is easy to design burdensome tests for someone else to do :)
This thread is way over my head. I have calculated BC using a single chronograph. By doing ten shot strings then moving the chronograph 30 yards and repeating the ten shot strings. I would use the average velocity of the near and far measurements to calculate BC.
Because I was using a very stable "archaic" springer with single digit extreme spreads the results were pretty plausible..
You can use two chronographs and skip the calibration if you use the results for comparison only. The numbers may not be exactly right for the occasion, but then again the BC of a specific projectile isn't a fixed number. As you know BC changes with velocity and the specific number would change depending on the testing velocities anyway.

I always hated the idea of using POI drop as a measure of BC because harmonics can throw bullets (and pellets) high or low (as well as left a right to a lesser degree). That skews the results possibly more than using uncalibrated chronographs.

Just my 2 cents in a million dollar thread. I'll shut up now.
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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #18 on: September 22, 2021, 09:26:27 AM »
Thanks for the input, Ron

I am happy with your single chrono use.  The reason for my elaborate suggestion is to satisfy those that would throw data out for not being "collected properly".
« Last Edit: September 22, 2021, 09:30:55 AM by subscriber »
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Offline Ribbonstone

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Re: Wind Drift Effect 20% Less on Pellets Shot from LW Poly Barrels?
« Reply #19 on: September 22, 2021, 12:30:36 PM »
First I thought...”BS”...rethought it, and perhaps not.

Claim for 20% lest drift didn’t list any strict testing methods...but it’s possible.

The old “our take” tests would shoot the same pellets in various airguns, and list the BC achieved.  Was the occasional test rifle that would show a large change in BC for the same pellets used in all the other test rifles.

My owne tests (two chronographs at different distances) also show a difference in BC between rifles, just not as much (then again, didn’t have that many rifles to test).  Same pellets, different BC’s just by what rifle shot them.


Because two individual rifles could have a pretty drastic change in BC, I’d now just assume that it was the barrel’s rifling that produced the change in drift.

Playing with a program….looking at drift @ 50 yards…. Would NOT take a giant numberic change in BC to earn 20% less drift @ 50 yards.  More like  a BC of .020 gong to .028.


Can go after it with velocity….but it takes a lot more.  Could get the same 20% less 50 yard drift with the same BC pellet  by boosting the velocity from 700fps to 950fps.

So maybe he really did see that kind of 20% change….but pinning it all on the bore shape is suspect.
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