When looking at slow motion videos of pellets traveling to a target, they sometimes "corkscrew" . Is that a problem with the pellet, or the barrel. Anyone know?
MOD EDIT: Moved to General Airgunning.
MOD EDIT: Moved to General Airgunning.
Why do pellets "corkscrew" ?
- Thread starter Mr.Gadgets
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I've seen this in some videos and from my understanding it usually happens with .177 or .22 being overpowered. The lighter pellets traveling at too great a velocity will encounter to much air turbulence for the weight of the pellet causing this effect. Now that I think about it Ted covered this in one of his videos.
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A dirty bbl. is often the culprit or just the wrong pellet for the gun. Also as FastEddie stated, over powering a pellet can cause it to be unstable. I recall an article on muzzle loaders where over powering caused the base of a soft lead bullet to mushroom. I wonder if over powering pellets causes the skirt to deform?
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I now have a ready-made reason for misses and fliers. I'm new to air gunning and didn't know about corkscrewing.
Thanks for posting the video.
Thanks for posting the video.
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These are the major problems...The first two are detrimental and the third sometimes is corrected after the bullet has reached some distance...
The "Corkscrew" is known as "Precession" ....Secong pic shows the cause for this.
The "Nutation' you can see in much in videos from the military shooting machine guns, etc...The circling sometimes gets smaller with distance while the bullet is finding its stabilizing mode.
Regards,
AZ
PS. Love your Dune Bug...Is it Meyers Manx over a shortened VW chasis?
The "Corkscrew" is known as "Precession" ....Secong pic shows the cause for this.
The "Nutation' you can see in much in videos from the military shooting machine guns, etc...The circling sometimes gets smaller with distance while the bullet is finding its stabilizing mode.
Regards,
AZ
PS. Love your Dune Bug...Is it Meyers Manx over a shortened VW chasis?
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I finally found it! I stumbled upon it years ago and luckily is still online. This is a nice flash "simulator" showing this precession and nutation effect. http://www.arld1.com/nutation.html
There are LOTS of other cool "simulations" too to understand better the theory behind airgunning.
There are LOTS of other cool "simulations" too to understand better the theory behind airgunning.
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That simulation is neat, but what actually causes this behavior? I've heard that commercial pellets are swaged from lead wire that may contain tiny voids or impurities, which would unbalance them. But this could just be marketing hype from people who want to sell you a pellet mold. A lot of people believe that pellet size makes a big difference, with oversized pellets being more likely to spiral. This seems like a sound theory. I've seen photos of oversize pellets pushed through a barrel where the rifling was clearly cut deeper on one side of the head, or the skirt was damaged in an asymmetric way by the choke or crown. A pellet damaged like that would tend to veer off to one side, but the fact that it's spinning keeps it in a spiral. A pellet with a thin skirt could probably also be bent if you seat it in the chamber by pushing on the skirt instead of using a probe to push it in by the head.
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It is know that too large of a pellet head diameter causes the cork screw flight. Even a too small head diameter isn't as bad as one that is too large. Also I have read that too high a velocity causes tumbling of the pellet. That's why I think you see reports of poor accuracy using PBA pellets.
When a pellet doesn't fly properly, you see really bad groups..like 3" at 50 yds. Even a too small head diameter isn't as bad as one that is too large.
When a pellet doesn't fly properly, you see really bad groups..like 3" at 50 yds. Even a too small head diameter isn't as bad as one that is too large.
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The biggest reason for a pellet to corkscrew, is that the head size of the pellet, is either too big or too small for your barrel.
I have a Steyr LG110 FT. I had great accuracy at short range, from like 10 to 25 yards. My best groups at 50 yards were like 5" to 10" group. At first I thought the barrel was dirty, and I would clean it untill I got a clean patch. Unfortunately it had no effect.
The pellets that I was shooting had a 4.52 head size diamator
then I saw the pellet sorting that Ted Bier did on Youtube, I went and bought different head size pellets in JSB. 4.50, 4.51, 4.52.
The berrel had it's best accurate groups with the 4.50 pellets. Now I shoot sub .2" groups at 50 yards.
Finally I have the accuracy that I have been expected from my rifle.
Biagio
I have a Steyr LG110 FT. I had great accuracy at short range, from like 10 to 25 yards. My best groups at 50 yards were like 5" to 10" group. At first I thought the barrel was dirty, and I would clean it untill I got a clean patch. Unfortunately it had no effect.
The pellets that I was shooting had a 4.52 head size diamator
then I saw the pellet sorting that Ted Bier did on Youtube, I went and bought different head size pellets in JSB. 4.50, 4.51, 4.52.
The berrel had it's best accurate groups with the 4.50 pellets. Now I shoot sub .2" groups at 50 yards.
Finally I have the accuracy that I have been expected from my rifle.
Biagio
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Spiraling at long range is because the translational velocity is slower than the rotational velocity, which does not slow down as much as the forward velocity, and past the apex, there is no upward component countering the downward gravitational force, only the gravitational component and the excess velocity in the rotational component goes past the counter balancing force of the translational force velocity.
Short range, use a high twist rate like 1:12 and translational velocity of well over 1,000 fps of a light pellet.
The farther the range you shoot; either, or reduce the twist rate like 1:48, heavy pellet, and velocities of well under 1,000 fps.
If you over spin a powder burner copper jacketed lead bullet, it will explode about ten yards ahead of the muzzle; unless it is a solid metal like CNC machined copper projectile.
The slightest irregularities in the pellets metallurgy alloy is greatly exaggerated the faster it is spun and a jump occurs, what we call spiraling.
In essence, the farther the range, the heavier the projectile, the slower the twist and translational velocity, and vice versa with short range like Olympic 10 meters, indoors, no wind component with a very light weight wadcutter, which has one of the worst ballistic coefficients, but at such short range and at approximately 567+/-10 fps, it does not matter because the pellet never reaches the apex of the trajectory.
Using mechanical statistics, spiraling can be predicted, the variables needed are the following:
Type of pellet
mass of pellet
dimensions of pellet
B.C. of pellet
Barrel active rifling length
Twist Rate
number of lands and grooves
dimensions of lands and grooves
choked or not choked
ambient temperature
relative humidity
barometric pressure
elevation above mean sea level
latitude
elevation shot angle
azimuth
wind velocity
wind direction
and a few others, and the range of spiraling can be predicted.
For example, a caliber sphere projectile of lead material needs a minimum of a 1:48 inch twist rate, where the caliber is equal to the diameter of the sphere ball.
Dry air is approximately 1/825 the density of water at room temperature, so imagine that every 825 feet (22.9167 yards) the pellet travels is like hitting a cube of one inch of water. The angle of hitting that one cubic inch of water is the wind velocity, so now imagine 2 x 825 inches (45.8333 yards) is like hitting two one cubic inch of water.
Do you think that would affect the pellets trajectory and maybe, just maybe cause it to start to spiral?
keep in mind that the pellet is not going through the whole one cubic inch of water, but just the caliber area.
density of an air molecule is 28.966 daltons, water is 18.016 daltons, which is why humid air has less density when the water molecules are in a gaseous state. A lead molecule density is 207.2 daltons, so using ratios and proportions you should be able to visualize the blob of lead we call pellet, flying through the air and water molecules.
In addition, shooting out to 100 yards, the pellet will fly through approximately 4.36 cubic inches of water, so do you think that will affect the pellets trajectory and performance?
In conclusion, numbers do not lie, but you can lie with numbers, and the laws of physics are not just really good ideas.
******!
Short range, use a high twist rate like 1:12 and translational velocity of well over 1,000 fps of a light pellet.
The farther the range you shoot; either, or reduce the twist rate like 1:48, heavy pellet, and velocities of well under 1,000 fps.
If you over spin a powder burner copper jacketed lead bullet, it will explode about ten yards ahead of the muzzle; unless it is a solid metal like CNC machined copper projectile.
The slightest irregularities in the pellets metallurgy alloy is greatly exaggerated the faster it is spun and a jump occurs, what we call spiraling.
In essence, the farther the range, the heavier the projectile, the slower the twist and translational velocity, and vice versa with short range like Olympic 10 meters, indoors, no wind component with a very light weight wadcutter, which has one of the worst ballistic coefficients, but at such short range and at approximately 567+/-10 fps, it does not matter because the pellet never reaches the apex of the trajectory.
Using mechanical statistics, spiraling can be predicted, the variables needed are the following:
Type of pellet
mass of pellet
dimensions of pellet
B.C. of pellet
Barrel active rifling length
Twist Rate
number of lands and grooves
dimensions of lands and grooves
choked or not choked
ambient temperature
relative humidity
barometric pressure
elevation above mean sea level
latitude
elevation shot angle
azimuth
wind velocity
wind direction
and a few others, and the range of spiraling can be predicted.
For example, a caliber sphere projectile of lead material needs a minimum of a 1:48 inch twist rate, where the caliber is equal to the diameter of the sphere ball.
Dry air is approximately 1/825 the density of water at room temperature, so imagine that every 825 feet (22.9167 yards) the pellet travels is like hitting a cube of one inch of water. The angle of hitting that one cubic inch of water is the wind velocity, so now imagine 2 x 825 inches (45.8333 yards) is like hitting two one cubic inch of water.
Do you think that would affect the pellets trajectory and maybe, just maybe cause it to start to spiral?
keep in mind that the pellet is not going through the whole one cubic inch of water, but just the caliber area.
density of an air molecule is 28.966 daltons, water is 18.016 daltons, which is why humid air has less density when the water molecules are in a gaseous state. A lead molecule density is 207.2 daltons, so using ratios and proportions you should be able to visualize the blob of lead we call pellet, flying through the air and water molecules.
In addition, shooting out to 100 yards, the pellet will fly through approximately 4.36 cubic inches of water, so do you think that will affect the pellets trajectory and performance?
In conclusion, numbers do not lie, but you can lie with numbers, and the laws of physics are not just really good ideas.
******!
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This thread looks at the root cause of pellet spiralling and what could be used to prevent it.
www.airgunnation.com
Pellet Spirals
Recently I got to thinking about shooting to ranges of 100 yards and the problems with pellet spiralling at the longer ranges, so I thought I would try to have a look at it for a couple of pellet designs. The two pellet designs are JSB pellets, not because they have particularly bad problems...
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Not necessarily
Couple weeks ago was testing a "TEST" barrel for KARMA AG's in .25 caliber shooting JTS 25.4 pellets.
We were at 1060 fps !!! and shooting straight and quite flat with shots at @ 40 & 66 yards sequentially showing ZERO spiraling, then took a few more shots near 100 yards ( Limited ability to do so safely as we had some folks out near the 100y target/s ) Had several others shoot the rifle with all present being pretty astonished that a pellet could be shot that fast and remain that stable
This was a personally pre prepped barrel having been hand lapped and bore waxed prior
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When my guns do this I just slow the pellet down and it pretty well cures the spiralling , Now I would really like to get some of those one off barrels like Motorhead has got,
Mike
Mike
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I would need both the barrel and a gun that could drive that pellet that fast. But Scott provided some interesting information which seems to pretty much prove a lot of speed does not have to lead to spiraling. The other theory I've heard is that cross wind can contribute to a tendency for spiraling. Theory is that the pellet may fly true in low wind but spiral if it encounters a cross wind. It would be interesting to hear what the wind was like in the example Scott provided and the twist rate of the subject barrel.
I do not have stability for pellets resolved in my brain at this point. For "bullets" stability is spin rate versus length of a projectile. Longer bullets have to spin faster to be stabile at long range. Slugs for air rifles are kind of like bullets but they seem to come with cavities on the front and back making them also a bit different. The "hybrid" design is quite different with an unusually large front cavity. But pellets can be at least somewhat stabile in flight without spinning due to their shape. Like a badminton shuttlecock. But we spin them. Seems more complicated. I've seen the stabilizing effect of pellet shape described as drag stabilized. While slugs have a bc that is higher numerically than pellets it is still low by bullet standards. Is that to preserve some drag stabilization?
I also agree with the comments describing spiraling as a reason to try a lower velocity. It seems like you need to shoot at 50 yards or more and film the flight of the pellet so you can slow it down to directly see the spiraling. That makes an investigation a bit more difficult. But given my inability to understand and predict spiraling checking for it seems like the rational choice. I've only shot at 100 yards occasionally. I get groups of 2-3 inches in normal a little bit windy weather. To me that does not suggest I am getting spiraling. I hoped for smaller groups than that but after looking at wind much more closely at my most typical 30 yard shooting distance I am not surprised at my 100 yard group size. A higher bc projectile would undoubtedly help.
I do not have stability for pellets resolved in my brain at this point. For "bullets" stability is spin rate versus length of a projectile. Longer bullets have to spin faster to be stabile at long range. Slugs for air rifles are kind of like bullets but they seem to come with cavities on the front and back making them also a bit different. The "hybrid" design is quite different with an unusually large front cavity. But pellets can be at least somewhat stabile in flight without spinning due to their shape. Like a badminton shuttlecock. But we spin them. Seems more complicated. I've seen the stabilizing effect of pellet shape described as drag stabilized. While slugs have a bc that is higher numerically than pellets it is still low by bullet standards. Is that to preserve some drag stabilization?
I also agree with the comments describing spiraling as a reason to try a lower velocity. It seems like you need to shoot at 50 yards or more and film the flight of the pellet so you can slow it down to directly see the spiraling. That makes an investigation a bit more difficult. But given my inability to understand and predict spiraling checking for it seems like the rational choice. I've only shot at 100 yards occasionally. I get groups of 2-3 inches in normal a little bit windy weather. To me that does not suggest I am getting spiraling. I hoped for smaller groups than that but after looking at wind much more closely at my most typical 30 yard shooting distance I am not surprised at my 100 yard group size. A higher bc projectile would undoubtedly help.
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