Correct speeds for pellets shooting for accuracy

[GHairgunner]

A recent discussion on speed of pellets for best accuracy at 100 yards, was great with a friend but I thought I would open it up and see what everyone else opinions might be. What flies everyday and finds the most stable and comfortable flight? Well airplanes for sure. Most fly around 600mph or 880fps. Looking at a website I looked for speeds of planes flying over storms, 624mph or 915 fps seemed to be the average. I'm guessing that some where in that range is the best place to be for speed shooting for accuracy.

Knowing that is that the average speed from gun to target?

Is it better to be at that speed the last quart of the distance?

Any other speed things to think about?

 

[Solo1]

Red wolves seem to all come shooting 22-25.4 @ 970 ?

 

[GHairgunner]

Red wolves seem to all come shooting 22-25.4 @ 970 ?

Mine come at least 970 or faster. Some of that is Utah sits around 5000 ft compared to 2000 at AoA. Our discussion went around just the pellet and not so much what it came out of. Let's say the wake of the air coming off the head and how it comes back to the skirt. Does the wake miss the skirt or does it reconnect with the skirt? Does wind change the shape of the wake? Does that change in the wake hit more on one part of the skirt and then affect the stability of the flight?

 

[Solo1]

Mine come at least 970 or faster. Some of that is Utah sits around 5000 ft compared to 2000 at AoA. Our discussion went around just the pellet and not so much what it came out of. Let's say the wake of the air coming off the head and how it comes back to the skirt. Does the wake miss the skirt or does it reconnect with the skirt? Does wind change the shape of the wake? Does that change in the wake hit more on one part of the skirt and then affect the stability of the flight?

I wish i knew all the dynamics but what i do know is 177 mrd’s are the same profile and seem to shoot the same way but then you said the jts shot better but they are shorter than mrd’s

 

[GHairgunner]

Interesting thought. I wonder if the curve of the head is different as well.

 

[Solo1]

Their also .01-.02 mm smaller head size

 

[Miles_M]

Forget aircraft, they fly in totally different environments under very different circumstances with very different deciding factors, such as fuel economy. Even shells from artillery weapons have a different set of conditions to consider, though they are affected in the same way by many of the variables, such as wind, yaw etc.

Pellets use a different method of stabilization to most projectiles, but they are still subject to the same laws of aerodynamics and ballistics. The aerodynamics are complicated by the combination of size and speed, which affects something called the Reynolds number and the effects of the Mach number. As an aside, pellets are not drag stabilized, as I hope to explain in a future thread.

Bob Sterne has shown that there is an optimum speed for minimizing cross wind effects. If the pellet is stable, the wind, even a crosswind, will not change the stability at all as the pellet will face into the total airflow direction and the wind will not blow onto the side of the pellet. The optimum speed to minimize wind effects is therefore driven by something called the lag time, which is the difference in flight time between the pellet with no drag and the real flight time in air, which is mainly affected by the pellet BC, which in turn is affected by the pellet design.

Group size is affected by pellet yaw, which in turn is affected by what happens in the gun and how the pellet reacts to it in flight. The gyroscopic stability factor is a major influence on how the pellet reacts, particularly at long range where spiralling can kill group sizes. It is all too easy with pellets to have too much stability for good group sizes. Again this is affected by pellet design.

Group size is affected by a large number of factors and is not simple to optimize. Speed on its own is not a major factor unless the speeds are getting close to sound speed, but other things which accompany getting and maintaining certain speeds can have major effects on how the pellet leaves the gun.

 

[rsterne]

IMO, the biggest variable beyond our mortal control is the wind.... If you know the drag of the pellet at various velocities, you can calculate the optimum muzzle velocity to minimize the wind drift.... For pellets, that is around 850-920 fps, depending on the range to target.... For slugs, which have significantly less drag, particularly in the low Transonic region (Mach 0.8-0.95), it is somewhat higher, around 980-1050 fps.... Because the drag curve is pretty flat around those velocities, you can edge upwards a small amount to flatten the trajectory without suffering too much of an increase in wind drift.... but don't go much beyond 950 for pellets or 1070 for slugs....

Bob

 

[hameditor]

Miles and Bob, thank you both for your explanations!

 

[Solo1]

Well this is what surprised me with the 22 barrel i got for the ghost. At 960 fps i was getting tight groups but with the 33.9 that i tried at the same time and speed wind drift was much more and more varried even when i slowed them down some. The mrds just didn’t seem to be as affected by the wind

 

[GHairgunner]

IMO, the biggest variable beyond our mortal control is the wind.... If you know the drag of the pellet at various velocities, you can calculate the optimum muzzle velocity to minimize the wind drift.... For pellets, that is around 850-920 fps, depending on the range to target.... For slugs, which have significantly less drag, particularly in the low Transonic region (Mach 0.8-0.95), it is somewhat higher, around 980-1050 fps.... Because the drag curve is pretty flat around those velocities, you can edge upwards a small amount to flatten the trajectory without suffering too much of an increase in wind drift.... but don't go much beyond 950 for pellets or 1070 for slugs....

Bob

It looks like some believe air craft speeds are close to where pellets have the most stabilized flight. What I think is the wake off the head of the pellet either interfaces with the skirt for a stable flight or is leading cause of destabilization.

Can one find a speed that causes the wake off the head of the pellet to inter acts with the skirt in a positive manner? In this picture the wake hits the skirt. What if the speed created a wake that misses the skirt and creates an aero dynamic affect of a boat tail bullet? Don't care about slugs at this point as they are not part of competitions I attend.

 

[Solo1]

It looks like some believe air craft speeds are close to where pellets have the most stabilized flight. What I think is the wake off the head of the pellet either interfaces with the skirt for a stable flight or is leading cause of destabilization.
View attachment 3968
Can one find a speed that causes the wake off the head of the pellet to inter acts with the skirt in a positive manner? In this picture the wake hits the skirt. What if the speed created a wake that misses the skirt and creates an aero dynamic affect of a boat tail bullet? Don't care about slugs at this point as they are not part of competitions I attend.

Have a look at this

https://journals.sagepub.com/doi/10.1177/1754337119831107

 

[GHairgunner]

Have a look at this

https://journals.sagepub.com/doi/10.1177/1754337119831107

Interesting there isn't more studies done in terms of designing better pellets. This study was done at 200mps which is 656fps, very slow even for the field target guys. Still thinking the frontal area of the pellet can move the air in wake form to the rear of the pellet. Even at the right speed get the wake to fall onto a boat tail form stabilizing the flight and increasing the BC as it pinches the pellet forward.

 

[Solo1]

I think the speed problem lies in the fact that most of these pellet studies are done in Europe at a 12 fpe limit. We need some american scientists to study them at higher velocity

 

[MountainSportAirguns]

Finding an all around "standard" speed for a pellet is imo impossible, even with two of the same guns using the same ammo. Actually testing what pellets do on paper in said gun is all that matters in the big picture. I have found usually, not always that most of my guns shoot pellets really well at 100 between 880 and 915. Most of the successful Benchrest shooters I've spoken to and shot with are in those range of speeds.

 

[Miles_M]

Have a look at this

https://journals.sagepub.com/doi/10.1177/1754337119831107

Unfortunately, the results and conclusions drawn from this report are biased by the fact that all of the designs chosen are high drag designs, with resulting low BC values. The "low drag design" looks to be as Superdome type pellet, which hardly qualifies as low drag.

As a result, the drag breakdown results are highly skewed towards the head drag which is given a vastly higher proportion than it should have, particularly if you are looking at JSB type designs with much rounder head shapes. This is shown up with the high calculated drag coefficient value which is over 0.5 compared with the measured JSB flight value of just over 0.3, i.e. only around 60% of the experiment value.

I have not studied the report enough to determine what went wrong in the experiment to give such high values. Certainly if you use standard reference sources to calculate the drag of the separate components you get a total much closer to the measured flight values and a lower total than the experimental value.

 

[Miles_M]

It looks like some believe air craft speeds are close to where pellets have the most stabilized flight. What I think is the wake off the head of the pellet either interfaces with the skirt for a stable flight or is leading cause of destabilization.
View attachment 3968
Can one find a speed that causes the wake off the head of the pellet to inter acts with the skirt in a positive manner? In this picture the wake hits the skirt. What if the speed created a wake that misses the skirt and creates an aero dynamic affect of a boat tail bullet? Don't care about slugs at this point as they are not part of competitions I attend.

The air turns through about 5 degrees from the head and interacts with the flare (skirt) to produce a stabilizing moment about the CG. This is what makes pellets aerogyro stabilized. The centre of pressure position is governed by the aerodynamic moments about the CG due to lateral forces and moments from the different components.

Boattails are destabilizing for projectiles, not stabilizing. A correctly designed boattail will reduce drag but makes a projectile less aerodynamically stable.

 

[GHairgunner]

The air turns through about 5 degrees from the head and interacts with the flare (skirt) to produce a stabilizing moment about the CG. This is what makes pellets aerogyro stabilized. The centre of pressure position is governed by the aerodynamic moments about the CG due to lateral forces and moments from the different components.

Boattails are destabilizing for projectiles, not stabilizing. A correctly designed boattail will reduce drag but makes a projectile less aerodynamically stable.

Finally someone with a number! So I modeled a 34gr 25 cal JSB pellet to use for illustration. Using the assumed 5 degree wake given unknown speed. You get a wild assumption I modeled below.

Now imagine by simply changing the speed of your pellet you could change the 5 degrees into 6 degrees thus changing how the pellet stabilizes during flight.

Now the question becomes at what speed is your pellet most resistant to wind affects, so lets say 800fps is the most stable then I should shoot my pellet from the barrel at a given speed so that while the pellet is traveling the last 20-25 yards to the target it falls into the 800fps range and enhances my scores.

The boat tail instability appears to be only the first 6-12 inches out of the barrel due to blow by of the high pressure of the explosion once bullet is in the air it seems to self correct according to 2 of the studies I read.

There really isn't any good studies available for pellet flight.

 

[Miles_M]

Finally someone with a number! So I modeled a 34gr 25 cal JSB pellet to use for illustration. Using the assumed 5 degree wake given unknown speed. You get a wild assumption I modeled below.
View attachment 3978
Now imagine by simply changing the speed of your pellet you could change the 5 degrees into 6 degrees thus changing how the pellet stabilizes during flight.
View attachment 3979
Now the question becomes at what speed is your pellet most resistant to wind affects, so lets say 800fps is the most stable then I should shoot my pellet from the barrel at a given speed so that while the pellet is traveling the last 20-25 yards to the target it falls into the 800fps range and enhances my scores.

The boat tail instability appears to be only the first 6-12 inches out of the barrel due to blow by of the high pressure of the explosion once bullet is in the air it seems to self correct according to 2 of the studies I read.

There really isn't any good studies available for pellet flight.

Boattails are destabilizing full stop. There can be no argument about that, and it has been well known for many years, as they produce a negative lateral force. If you are reading something which says anything different, stop reading it, it is rubbish.

I am beginning to think that you are believing that a more stable pellet will somehow keep going in the same direction and ignore the wind. All the stability can do is turn the pellet to face into the total relative airflow, it does not in any way affect the down wind drift. The minimum down wind drift will be achieved at a speed governed by the shape of the projectile drag coefficient curve, and for pellets is at speeds around 900 ft/sec at the muzzle, around 1000-1050 ft/sec for slugs due to their different drag curve shape.

Just because you change the speed, it does not mean the airflow angle will change to a large degree, unless you are getting towards sonic velocities where larger changes may occur. If the angle does change and more of the projectile flare is exposed to the airflow, the projectile drag will increase, which will in turn increase the down wind drift. All wind induced errors at the target are more affected by the wind close to the gun than close to the target. Cross winds produce an angular error into the trajectory, so it is simple geometry that the angular error at the gun end of the trajectory will have a bigger effect than the angular error near the target.

I have an old thread which explains how a cross wind effects a pellet. Hopefully I can add it on this site sometime soon after the rest of the stability threads.

 

[GHairgunner]

Boattails are destabilizing full stop. There can be no argument about that, and it has been well known for many years, as they produce a negative lateral force. If you are reading something which says anything different, stop reading it, it is rubbish.

I am beginning to think that you are believing that a more stable pellet will somehow keep going in the same direction and ignore the wind. All the stability can do is turn the pellet to face into the total relative airflow, it does not in any way affect the down wind drift. The minimum down wind drift will be achieved at a speed governed by the shape of the projectile drag coefficient curve, and for pellets is at speeds around 900 ft/sec at the muzzle, around 1000-1050 ft/sec for slugs due to their different drag curve shape.

Just because you change the speed, it does not mean the airflow angle will change to a large degree, unless you are getting towards sonic velocities where larger changes may occur. If the angle does change and more of the projectile flare is exposed to the airflow, the projectile drag will increase, which will in turn increase the down wind drift. All wind induced errors at the target are more affected by the wind close to the gun than close to the target. Cross winds produce an angular error into the trajectory, so it is simple geometry that the angular error at the gun end of the trajectory will have a bigger effect than the angular error near the target.

I have an old thread which explains how a cross wind effects a pellet. Hopefully I can add it on this site sometime soon after the rest of the stability threads.

Close on the stable pellet. Wind will always change the direction, the better I get at reading the wind the better my scores. What I'm going after is the sudden 5 or 6 instead of a 8 or 9. Usually caused by a spiral or unusual jumps from intended target. This is where I believe the wind hits the skirt and makes the head spin off axis. The resulting low and high pressure created on the pellet and the resulting spiral or unpredicted movement. These weird direction changes never happen at the gun (although wind speed does have the greatest effect on accuracy at the gun) they always happen down range in the last 20-25 yards. My goal is to explore pellet speeds in conjunction to accuracy and a severe reduction in spirals and unexplained direction changes.