6,10,12, what effect does more/less have on projectiles, diablo or non waisted,
thank you.
thank you.
lands grooves numbers effects
- Thread starter harrymoreland
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Hmm looking at it from a pellet perspective too many may distort the pellet as there is increased pressure from the lands. Were I feel for a slug too many hurt speed as there is a lot more slug surface touching the lands and causing more friction. Hopefully someone with machining experience will drop their two cents.
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The number of rifling impressions and their geometry affect a projectile's flight by way of the Magnus effect.
https://en.wikipedia.org/wiki/Magnus_effect#In_external_ballistics
A couple of intriguing demonstrations:
https://www.youtube.com/watch?v=2OSrvzNW9FE
https://www.youtube.com/watch?v=K6geOms33Dk
It is perhaps helpful to think of the rifling impressions as little rudders wrapping around the perimeter of the projectile. As the bullet spins, these little rudders catch the air and exert a force on the bullet. So for example imagine two bullets, one with a smooth uninterrupted perimeter and another with several very deep, squared-off impressions. Intuitively, which one will be affected more by a crosswind?
https://en.wikipedia.org/wiki/Magnus_effect#In_external_ballistics
A couple of intriguing demonstrations:
https://www.youtube.com/watch?v=2OSrvzNW9FE
https://www.youtube.com/watch?v=K6geOms33Dk
It is perhaps helpful to think of the rifling impressions as little rudders wrapping around the perimeter of the projectile. As the bullet spins, these little rudders catch the air and exert a force on the bullet. So for example imagine two bullets, one with a smooth uninterrupted perimeter and another with several very deep, squared-off impressions. Intuitively, which one will be affected more by a crosswind?
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The above videos seem to illustrate the maximum effect possible from Magnus effect-direction of rotation ALONG the axis of travel. A bullet (or pellet) with it's rotation PERPENDICULAR to the axis of travel would seemingly experience many magnitudes less effect compared to those illustrations. A barely detectable breeze will have profoundly more effect on any projectilie, IMO.
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I agree 100% and the Wikipedia article linked above states:
”Overall, the effect of the Magnus force on a bullet's flight path itself is usually insignificant compared to other forces...”
I figure that’s why it is a topic that seldom intrudes upon the conversation.
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I have machining experience, but its not needed for this topic. Shooters have proven over the centuries that a smoothbore can be slightly faster than a rifled bore, but the rifled one is typically more accurate. Its more an issue of salesmanship as to how many grooves gives best accuracy, if there are at least two, as anyhing from two to over twenty grooves has worked in target guns.
I think its harder to make two or three groove barrels due to the extra metal to be pushed around or even removed, but I am a proponent of 2 grooves becuase its easier to inspect to determine if both grooves are identical. But few machinists in their right minds are making their own rifled barrels, since really good ones can be purchased for relatively little money by companies with expensive tooling and good skills to make such specialized stuff. I can make an airgun, but I buy the barrels.
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I think It depends on the power level and projectile weight/mass. Airguns show at far lower power and speed and therefore should be affected more by the magnus affect. It still should be relative small unless we are taking about 100 plus yard due to the amount of time the projectile in the air. Also slugs might see more affect Freon it just because the rifle marks are much longer and catches much more air than just edge of the skirt.
But it is obvious sharp edge will have significant aerodynamic affects compared to smooth edges, just look at the air plains or missiles. However it is hard to quantify in our application unless there is side by side test with identical everything. Sounds like fun experiment though.
But it is obvious sharp edge will have significant aerodynamic affects compared to smooth edges, just look at the air plains or missiles. However it is hard to quantify in our application unless there is side by side test with identical everything. Sounds like fun experiment though.
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Here's a wind drift diagram that has been shared on the forums. I've added a couple of markups to highlight the effect we are talking about:
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Sorry, I incorrectly attributed the vertical shift in the above diagram to the Magnus effect. A respected ballistician explains it is the result of aerodynamic jump which is related to the projectile yawing slightly in an attempt to align itself to the crosswind. I suppose that is more reason to not concern ourselves with the Magnus effect.
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L= Lands, G = Grooves.
I was wondering if , say, 12 sets of L/G each set , say 3mm* (1mm of L, 2mm of G) would impart more or less twist upon the projectile (while in the barrel) than 6 sets 0f 6mm (2mm 0f L, 4mm of G).
Also, would the number effect the speed the projectile would achieve, again while still in the barrel.
There is some information regards this subject in relation to power burners, ie, less grooves = more speed.
However little info I can find regards the effects (it any) it would have in air power world, and air power speeds, where (perhaps) more groove (less land = less drag) may = more speed.
*Note, please excuse the "3mm" "6mm" ect units of measure, I pulled them out of my A**, sorry, thin air.
Also, I am not an expert, in anything, so if this is all nonsense, don't be kind, Just put me right.
thanks
good luck.
I was wondering if , say, 12 sets of L/G each set , say 3mm* (1mm of L, 2mm of G) would impart more or less twist upon the projectile (while in the barrel) than 6 sets 0f 6mm (2mm 0f L, 4mm of G).
Also, would the number effect the speed the projectile would achieve, again while still in the barrel.
There is some information regards this subject in relation to power burners, ie, less grooves = more speed.
However little info I can find regards the effects (it any) it would have in air power world, and air power speeds, where (perhaps) more groove (less land = less drag) may = more speed.
*Note, please excuse the "3mm" "6mm" ect units of measure, I pulled them out of my A**, sorry, thin air.
Also, I am not an expert, in anything, so if this is all nonsense, don't be kind, Just put me right.
thanks
good luck.
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https://www.youtube.com/watch?v=CAR1myxvFjs&t=1538s
Great video from our buddy Matt Dubber (AirArmsHuntingSA) that addresses this. Very interesting what he has to say about it.... Specifically the 1st barrel he scopes. The standard (VERY popular) LW barrel with 12 lands and a 1:17.7 twist. All I can say is if you're striving for extreme long range accuracy with slugs out of this barrel, you're chasing the wind.
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Is the pedigree of successful long-range guns dominated by 2-groove barrels?
I suspect Matt is ascribing too much significance to the land/groove count.
(Twist rate is a different matter altogether. There is no good/better/best in the general sense. Rather, it is dictated by whatever projectile is being shot.)
I suspect Matt is ascribing too much significance to the land/groove count.
(Twist rate is a different matter altogether. There is no good/better/best in the general sense. Rather, it is dictated by whatever projectile is being shot.)
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Understood, and I agree with your last sentence wholeheartedly. . I wanted to focus in on the LW barrel only, and the land/groove count vs the twist rate. Since the majority of air rifle manufacturers use LW barrels, and the pinnacle of the sport is long range accuracy with slugs, I wanted the readers to know that achieving this goal with the stock LW barrel is going to difficult if not impossibl. FX has cornered the market of blending twist and land/groove design (if you even want to call the smooth twist barrels inner workings lands and grooves) to achieve fabulous short and long range accuracy with pellets and slugs.
But if any of you guys are interested in a barrel with a faster twist, or different inner dimensions than the stock LW barrels, then hit up Alex in the Russian Republic. His email address is [email protected] . He will make you a custom barrel and ship it to your door for cheaper than you can buy a stock barrel from the manufacturer. But you'll need to be patient for the process. The item gets hung up in customs, so after he ships it and sends you a tracking number, it may be 3-4 weeks before you see that it's in the hands of the US Customs.
But if any of you guys are interested in a barrel with a faster twist, or different inner dimensions than the stock LW barrels, then hit up Alex in the Russian Republic. His email address is [email protected] . He will make you a custom barrel and ship it to your door for cheaper than you can buy a stock barrel from the manufacturer. But you'll need to be patient for the process. The item gets hung up in customs, so after he ships it and sends you a tracking number, it may be 3-4 weeks before you see that it's in the hands of the US Customs.
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