Supersonic Transition

[justin amateur]

The subject of supersonic transition and how it affects rimfire trajectories has caught my interest.
I've been trying to locate information regarding studies and articles with actual data, not anecdotal reports.
All the articles I've found go back to a study done on a Sierra bthp, which is not applicable to the typical 22lr, 22wmr.
A long slender bullet is unable to make it through the transition due to the shift in center of pressure.
Being stern heavy it begins to yaw or tumble which ruins results on target.
The 22lr and 22wmr are stubby round nose projectiles and appear to be minimally affected by the transition.
My target results at 200 yards show wind, gravity and cartridge defects being the major problems.

Any further information available documenting actual testing?

 

[rick137]

My post "BRL Study of RWS 50 and Tenex Exterior Ballistics" contains link to the document and may be of interest.

 

[justin amateur]

That's the Aberdeen rimfire ballistics study by McCoy.
Found that one, but it didn't really cover the transition from what I can tell.
Both cartridges are subsonic match ammo.

http://www.dtic.mil/dtic/tr/fulltext/u2/a229713.pdf

 

[rick137]

In what range of speeds are you interested? And what aerodynamic parameters?

 

[justin amateur]

At this stage, I'll read everything available.
What I know is the bare minimum from the original study with the SMK.
I see many blaming the transition for their results
but it could more likely be cartridge defects or wind related.
My own experience shows the 22lr has minimal deflection during the transition.
Vertical spread matches results calculated based on mv differences and time of flight.
If there were trajectory shifts during the transition there would be no match.
My thought is that the bullet shape of the 22lr does not suffer the dynamic instability as the SMK produced.
If the 22lr bullet is minimally affected, then most pistol and other short/round nosed projectiles
would be minimally affected by the transition also.

 

[JG26_Irish]

This is an interesting subject. The Aberdeen rimfire ballistics study by McCoy was using Eley, RWS and Ultra Match ammo loaded to std velocity mach grade specs but also included some custom loaded ammo both faster and slower. It was significant that the study recorded velocities up to 1.05 mach and that the spark shadow photos recorded trans-sonic shock waves on the bullets ranging from 0.97 mach to 0.85 mach indicating that the bullets were still transonic at those speeds. It was also interesting that the study observed bullets at 950fps exhibited 20% less wind sensitivity than the std velocity of 1090 fps.

A hypothesis or two may be made based upon that limited information:
1.) Since the match grade bullets are travelling smack in the middle of the transonic speeds of 0.85-0.95 mach for most of their effective flight, there is little evidence to show that the supersonic transition and its related shock waves are greatly hampering the bullets at those slightly subsonic speeds. My own use of supersonic 22lr hunting loads for 200y groups also seems to support a hypothesis that the transition is not making as much difference as other greater variables such as wind and muzzle velocity variances.

2.) Since the slower 950fps bullets exhibited less wind sensitivity than the faster 1090fps samples, this might indicate that the large shock wave surrounding the bullets traveling in the 0.90-1.00 mach range might be getting blown off course by the wind and dragging the bullet along with it. I am not being very eloquent with my words but you should get the gist of what I am saying. Is it possible that a bullet with an attached supersonic shock wave makes for a larger surface area to be blown around?

I have noticed before that the Eley nose bullet currently in use with the Match-Black and 10x product of today seems to be less sensitive to wind than the more traditional bullet used by RWS, Lapua and others today. This is anecdotal and not proven with a scientific method. I noticed in the study that the Eley nose bullet was harder (Brinell number = 10). I wonder if that is still true and if this results in a fired bullet will less deformation and thus less wind sensitivity? If you have every watched your 22lr bullets as they fly down range (the light must be just right to do so) you will observe that the bullet's path is like that of a curve ball as it arcs up and down in its rainbow trajectory, it is also arcing from left to right even if there is no wind whatsoever. It is worth pondering some more.

Irish.

 

[rick137]

This is an interesting subject. The Aberdeen rimfire ballistics study by McCoy was using Eley, RWS and Ultra Match ammo loaded to std velocity mach grade specs but also included some custom loaded ammo both faster and slower. It was significant that the study recorded velocities up to 1.05 mach and that the spark shadow photos recorded trans-sonic shock waves on the bullets ranging from 0.97 mach to 0.85 mach indicating that the bullets were still transonic at those speeds. It was also interesting that the study observed bullets at 950fps exhibited 20% less wind sensitivity than the std velocity of 1090 fps.

A hypothesis or two may be made based upon that limited information:
1.) Since the match grade bullets are travelling smack in the middle of the transonic speeds of 0.85-0.95 mach for most of their effective flight, there is little evidence to show that the supersonic transition and its related shock waves are greatly hampering the bullets at those slightly subsonic speeds. My own use of supersonic 22lr hunting loads for 200y groups also seems to support a hypothesis that the transition is not making as much difference as other greater variables such as wind and muzzle velocity variances.

2.) Since the slower 950fps bullets exhibited less wind sensitivity than the faster 1090fps samples, this might indicate that the large shock wave surrounding the bullets traveling in the 0.90-1.00 mach range might be getting blown off course by the wind and dragging the bullet along with it. I am not being very eloquent with my words but you should get the gist of what I am saying. Is it possible that a bullet with an attached supersonic shock wave makes for a larger surface area to be blown around?

I have noticed before that the Eley nose bullet currently in use with the Match-Black and 10x product of today seems to be less sensitive to wind than the more traditional bullet used by RWS, Lapua and others today. This is anecdotal and not proven with a scientific method. I noticed in the study that the Eley nose bullet was harder (Brinell number = 10). I wonder if that is still true and if this results in a fired bullet will less deformation and thus less wind sensitivity? If you have every watched your 22lr bullets as they fly down range (the light must be just right to do so) you will observe that the bullet's path is like that of a curve ball as it arcs up and down in its rainbow trajectory, it is also arcing from left to right even if there is no wind whatsoever. It is worth pondering some more.

Irish.

If your hypothesis is correct, then would the CRF of the Vudoo lead to bullets with less deformation and therefore less wind sensitivity?

 

[justin amateur]

Still hunting information, found this one
Army Research Lab 9mm

https://drive.google.com/open?id=16GK2lfmH1OZGu3B5VfmBSdcP_kpz_zFT


Below is the article folks use as an excuse as to the cause of poor target results.

http://www.accurateshooter.com/ballistics/transonic-effects-on-bullet-stability-bc/

Note, it relates solely to a long slender bthp, not stubby round nose bullets.
Bryan Litz comments that other projectile shapes will be affected differently.

 

[lash]

This is an interesting subject, as I am guilty of repeating the anecdotal axiom that the supersonic .22 LR loads do not transition well. Usually when someone is complaining about them at 200-300+ yards.

 

[justin amateur]

Which raises the question: How can you determine the cause of the trajectory shifts?
Outdoors, with rimfire of questionable quality, is it wind/turbulence related, cartridge defects,
asymmetric projectile deformed by the rifling/barrel? My interest was caught when I noticed
that the 50 shot group at 200 yards from a 42 grain Eley subsonic matched the spread
from a 42 grain Eley supersonic. If the transition through the sound barrier occurred
shouldn't there have been a measurable difference? Based on the ballistics chart
transition takes place in the first 50 yards, leaving the remaining 150 yards to amplify
any shift in the projectiles trajectory. Didn't happen.

 

[lash]

Still hunting information, found this one
Army Research Lab 9mm

https://drive.google.com/open?id=16GK2lfmH1OZGu3B5VfmBSdcP_kpz_zFT


Below is the article folks use as an excuse as to the cause of poor target results.

http://www.accurateshooter.com/ballistics/transonic-effects-on-bullet-stability-bc/

Note, it relates solely to a long slender bthp, not stubby round nose bullets.
Bryan Litz comments that that other projectile shapes will be affected differently.

Those are good articles, but without verified ballistic coefficient numbers for the snubby .22 projectiles at the various supersonic, transonic, subsonic and transition periods; still doesn’t get us any closer to an answer. There’s no valid way to model them without those verified inputs.

 

[kabarNC]

I'm guilty as well for spewing hearsay on the negative effects of supersonic transition and how it relates to 22LR. I'm also interested in learning more about this. Thanks for the thread..

 

[lash]

Which raises the question: How can you determine the cause of the trajectory shifts?
Outdoors, with rimfire of questionable quality, is it wind/turbulence related, cartridge defects,
asymmetric projectile deformed by the rifling/barrel? My interest was caught when I noticed
that the 50 shot group at 200 yards from a 42 grain Eley subsonic matched the spread
from a 42 grain Eley supersonic. If the transition through the sound barrier occurred
shouldn't there have been a measurable difference? Based on the ballistics chart
transition takes place in the first 50 yards, leaving the remaining 150 yards to amplify
any shift in the projectiles trajectory. Didn't happen.

Valid questions.

 

[rick137]

Those are good articles, but without verified ballistic coefficient numbers for the snubby .22 projectiles at the various supersonic, transonic, subsonic and transition periods; still doesn’t get us any closer to an answer. There’s no valid way to model them without those verified inputs.

And what about the many other aerodynamic forces besides the drag coefficient. Do they ever play a role in a 22LR trajectory? And if so at what range do they become important?

In "Rifle Accuracy Facts" H. Vaughn addressed some of these issues for centerfire ammunition in a rifle.

Remember what constitutes a good experiment/test: one independent variable, one dependent variable and all other variables either known quantitatively and effect accurately calculable or insignificant.

Fun to ponder but not as much fun as shooting.

 

[justin amateur]

How would you test for transition caused trajectories?
I can compute vertical spread based on mv differences.
So it would be possible to compare the vertical effects on target
as computed, versus as produced. Shoot indoors from a fixture.
Chronograph everything, but still won't eliminate cartridge defects
or asymmetric projectiles. How large a sample is needed?

 

[steve123]

Sure would be nice if the better ammo Co's made a 45 grain match bullet with higher BC that went 950 fps so we don't have to consider supersonic transition problems.

Might need a faster twist barrel though???

 

[MDrimfirerookie]

hopefully not throwing this thread too far off track but damn, if i would have known how it would play out in real life, i would have paid more attention in physics in school (and yes i know there is more than physics in play, just generalizing)

in all seriousness though thank you for starting this thread and the thought provoking questions herein. i'm watching intently

 

[justin amateur]

Another study with 9mm and 5.56

https://drive.google.com/open?id=11NWmh4V4YAy1v1_rRSdIqhTNqgqm6TYV

Checked the ammo locker, there's a box of Eley Hi-V in there.
Rated 1250 fps, 1128 fps is mach here at sea level.
The next calm morning, I'm going to send 50 at a single aimpoint
at 200 yards and compare chrony numbers to vertical spread.
It'll be a rough method to determine if there is a transition deflection.

 

[rick137]

hopefully not throwing this thread too far off track but damn, if i would have known how it would play out in real life, i would have paid more attention in physics in school (and yes i know there is more than physics in play, just generalizing)

in all seriousness though thank you for starting this thread and the thought provoking questions herein. i'm watching intently

No, there is not more than physics in play with mass x acceleration = force and moment of inertia x angular acceleration = torque the underlying equations. In full complexity calculation of the trajectory requires knowing the three components of the center of mass of the bullet and the three directions of the instantaneous rotational axis as a function of time from muzzle to target. So called 6 DOF ballistics. Same as with a football. A rifle bullet leaving the muzzle is rotating very rapidly, several hundred thousand rpm and may have a speed greater than speed of sound. Not only must the external geometry of the bullet be known but the density at every point in the interior. Any deviation of either the external geometry or from perfect cylindrical symmetry is definitely bad news. The force of gravity and at long distances the Coriolis force since Earth is rotating are well known. The really difficult forces result from interaction of bullet with the atmosphere. Each of these forces has an associated coefficient which must be know to calculate the effect of that force on the bullet. They can be measured or derived numerically through computational fluid dynamics on a supercomputer. Even if all that is known you are not home free. The bullet velocity must be known after passing through the ejecta field and gas generated by the shot. Then the thermodynamic properties of the atmosphere between the muzzle and the target. Then the killer, the three components of the wind velocity at every location of the bullet between the muzzle and the target.

Excluding the experiments the CalTech Jet Propulsion Lab could do the calculations for you. To appreciate the complexity look at McCoy's "Modern Exterior Ballistics."

 

[rick137]

Another study with 9mm and 5.56

https://drive.google.com/open?id=11NWmh4V4YAy1v1_rRSdIqhTNqgqm6TYV

Checked the ammo locker, there's a box of Eley Hi-V in there.
Rated 1250 fps, 1128 fps is mach here at sea level.
The next calm morning, I'm going to send 50 at a single aimpoint
at 200 yards and compare chrony numbers to vertical spread.
It'll be a rough method to determine if there is a transition deflection.

Aerodynamic jump if there is a crosswind.

 

[MDrimfirerookie]

wow, impressive. the older i get the more i regret taking "rocks for jocks"

So my reading list already has Bryan Litz's books on it, now I'll add your suggestion of McCoy.

Any others?

 

[rick137]

wow, impressive. the older i get the more i regret taking "rocks for jocks"

So my reading list already has Bryan Litz's books on it, now I'll add your suggestion of McCoy.

Any others?

On the other hand, I majored in geophysics and was a nerd without a date.

I learned about WEZ analysis from one of Litz' books. One of the most valuable items in my firearms conceptual tool chest.

If you want to learn physics from the ground-up study Feynman's Lectures of Physics although only Volume I would be of direct interest. Beware however that Feynman was a genius and takes no prisoners. Requires mucho intellectual perspiration. Directly relevant is "Ballistics - Theory and Design of Guns and Ammunition" by D.E. Carlucci and S. S. Jacobson.

H. Vaughn wrote "Rifle Accuracy Facts" to describe his research into the factors determining the accuracy of hunting rifles/ammunition. This guy was the real meal deal. Conclusions might be somewhat dated since book about 20 years old but the methodology never will be. Unfortunately book out of print and scalpers want royal ransom.

I do not learn quickly so have to return over and over to these books.

 

[justin amateur]

After 5 days of chasing linked articles, all the blame for 22lr and 22wmr inaccuracies
due to supersonic transition, link back to the original study of the SMK.
Nowhere did I find any information supporting the idea that the stubby round nose bullet is affected the same way.
All are using the SMK study as an excuse.
I wonder if the folks at Lapua might have any information?

 

[JG26_Irish]

If your hypothesis is correct, then would the CRF of the Vudoo lead to bullets with less deformation and therefore less wind sensitivity?

I have not had hands on the Vudoo yet. What is the "CRF"? I cannot respond since I do not know what that is. I have an old colleague at JPL in Pasadena if we need tech support. I have not talked to him since I escaped California, but I think he is still there working on the MARs exploration program. Also have another colleague who worked for Lockheed rocket systems and is now with Space-X. They are used to making long precision shots, lol.

I have noticed that even with the match grade ammo like Lapua or Eley, I see a pronounced wobble in the bullets as if the spinning bullet has some longitudinal misalignment with its flight path as if it is only marginally stable. Search youtube for video of 22lr bullets in flight. The wobble is noticeable. Another item not being considered is the bbl harmonics. There is a reason the bench rest crowd is using adjustable muzzle dampeners to reduce movement of those vibrations at the muzzle crown. I believe that a lot of the benefits of ammo lot testing is finding a lot of high grade match ammo whose velocity also matches the harmonic natural frequency of that given rifle barrel to naturally minimize these vibrations. I have also seen 20% group size improvements by installing such dampeners on the muzzle of a Remington match rifle which was already using a tested and optimized ammo lot. I further have seen an old Win Mod 52 which shot OK and 1/2" groups with a modern receiver mtd optic tighten up noticeable when I installed an old school bbl mounted optic. I think the optic bridged much of the length of the bbl making it functionally stiffer and reduced the natural vibrations of the bbl. Result was tighter groups.

 

[lash]

CRF = controlled round feeding

 

[rick137]

JG26_Irish

Everything you say is right on.

My understanding is CRF means round is chambered without bullet contacting any part of receiver or barrel. The case must be held by the rim once round picked-up by bolt?

The goal of interior ballistics is prediction of the speed and direction of the center of mass and longitudinal axis of rotation of the bullet at the muzzle. Also important is the actual bullet shape at the muzzle and how that differs from manufactured bullet shape. Next is the transition zone, which extends from muzzle to where bullet is traveling faster than the ejecta and high pressure gas generated by the shot. If the bullet is deformed the interaction of the bullet with the ejecta and high pressure gas will alter its trajectory. Dispersion results if the deformation varies between bullets. Finally exterior ballistics.

The interior ballistics of a rifle could be modeled using FEA, finite element analysis. The discretizing mesh would have to be fairly fine for precision but that is probably not half of the effort. The anelastic properties, i.e. elastic plus damping, for every component of the rifle must be known, barrel receiver, stock.... Even assuming the material properties of each component are isotropic, that means shear modulus, bulk modulus, shear attenuation coefficient, bulk attenuation coefficient must be determined. Then the external loading, i.e. how the rifle is support. This may be time dependent once the powder is ignited. FEA could also model the ignition and burning of powder given their physical and chemical properties. Finally the forces and torques generated by bullet traveling down the barrel.

All of the above create the barrel harmonics of which the most important are the vertical and horizontal flexural modes. At some level of accuracy perhaps it is sufficient to consider a barrel as a clamped tube and determine its vibrational modes. As you noted anything connected to or contacting the barrel will affect the harmonics for better or worse. justin amateur has duly noted the effect of ammunition on vertical dispersion from variations in muzzle velocity. Variations in harmonics from difference in amount and timing of energy released in combustion of the power will have an effect at some level of accuracy.

 

[trophyhunter]

So I’ll throw my $.02 into this conversation after reading it a few times. I don’t have all the info from articles but I have info on bullets and variances in ammo. So today after reading this the first time I decided to see what made “match” ammo as the name says. I weighed 20rds of golden bullets for giggles. Most the ammo weighed 49.2-50.4 so a difference of 1.2grains. Taking the bullet to be 40g the rest is case, primer and what little powder is in the case. I should’ve weighed a case. I will tomorrow. On SK standard plus I was getting a variance of .4g. The average and most common weight was 51.7g, I had 2 at 51.9 and 5 at 51.5g. So if i remove the bullet weight of 40g I’m left with 11.7g average for the bulk of ammo. If you figure out the .2 difference high or low it’s 2% I think in powder,primer,case weight. If you added that much to a centerfire rifle case for most calibers it would be ALOT.
Could that be the difference and variance that many are seeing.

Ok I’ll shut up now

Gilbert

 

[rick137]

G

So I’ll throw my $.02 into this conversation after reading it a few times. I don’t have all the info from articles but I have info on bullets and variances in ammo. So today after reading this the first time I decided to see what made “match” ammo as the name says. I weighed 20rds of golden bullets for giggles. Most the ammo weighed 49.2-50.4 so a difference of 1.2grains. Taking the bullet to be 40g the rest is case, primer and what little powder is in the case. I should’ve weighed a case. I will tomorrow. On SK standard plus I was getting a variance of .4g. The average and most common weight was 51.7g, I had 2 at 51.9 and 5 at 51.5g. So if i remove the bullet weight of 40g I’m left with 11.7g average for the bulk of ammo. If you figure out the .2 difference high or low it’s 2% I think in powder,primer,case weight. If you added that much to a centerfire rifle case for most calibers it would be ALOT.
Could that be the difference and variance that many are seeing.

Ok I’ll shut up now

Gilbert

Gilbert:

If my understanding is correct, conventional wisdom has the load achieving the best accuracy for centerfire ammunition does so because it generates the least flexural vibration at the muzzle at the time the bullet exits the barrel. So your hypothesis has much merit with the amount of energy released being the most significant factor causing flexural vibrations and differences in flexural vibrations from shot to shot. Another factor could be the rate at which energy is released. These two factors may be the reasons why rimfire rifles "like" one brand of ammunition. Either the flexural vibrations are small, the differences in flexural vibrations are small or both.

Other contenders are the differences in weight of the bullet, the homogeneity of its density and its geometry after it leave the muzzle. Are these differences greater in rimfire than centerfire ammunition?

 

[justin amateur]

I've dissected quite a few rimfire cartridges.
The 4 biggest differences I've found
between match quality and other rimfire
have been primer amounts, brass dimensions,
bullet symmetry (or lack of) and seating differences.
Visual inspection of the components
showed irregular seating depths and angle,
smeared driving bands, irregular heels,
varying brass diameters/lengths/widths
and varying amounts and locations of primer.

I've never found a brand of rimfire any of my rifle's liked.
I've found a box or two and an occasional brick that did very well,
but the next box or brick didn't, as evidenced by results on target and chrony numbers.
I think that "find the brand y'er rifle likes" cr*p
is a marketing gimmick parroted by retailers to improve sales.
Another internet "truism" that ain't.

 

[trophyhunter]

So I decided to dive further into this abyss to see why i have the random flyer at 300yds

What I found is the amount of variance. While it’s very minimal in general but based on the amount of powder and % that it increase or adds would lead to a big amount.

I weighed 25 cases and had 18 weigh 51.7g total then subtracted the theoretical bullet weight, and weighed all the cases. I was impressed that all except 1 was 10.1g.

The 7 I had were a spread of .2g or 12.5%

If that was a center fire and either bullet or powder was 12.5% more it would be brutal. For my BRA I use 31.6g that would be 35.55g of powder.....

So it would lead me to believe that weighing loaded ammo would add another level of accuracy to rimfire.

Next I am going to weigh, sort, mark and chrony to see if the variances show up in the speed.

 

[justin amateur]

If you have the time try this...

Box of 50 rimfire ammo of y'er choice.
Weigh a cartridge.
Disassemble the cartridge
Weigh the bullet, weigh the powder, weigh the primered brass.
Look inside the brass at the primer application.
Note where it's at and how much up the inside of the brass it runs.
Ignite the primer then brush out the residue so the interior is clean.
Weigh the empty brass.
The difference in before and after will give the primer amount.
Add the totals to verify it matches the original cartridge weight.
You might be annoyed by bullet and primer weight differences.

 

[lash]

If you have the time try this...

Box of 50 rimfire ammo of y'er choice.
Weigh a cartridge.
Disassemble the cartridge
Weigh the bullet, weigh the powder, weigh the primered brass.
Look inside the brass at the primer application.
Note where it's at and how much up the inside of the brass it runs.
Ignite the primer then brush out the residue so the interior is clean.
Weigh the empty brass.
The difference in before and after will give the primer amount.
Add the totals to verify it matches the original cartridge weight.
You might be annoyed by bullet and primer weight differences.

First of all, may I just say that I am impressed as all get out by someone who has the dedication to do all of that and record it. I make the assumption that you have already done so, especially after reading a number of your posts and your conclusions.

Now I’ll say that there’s is no way that I’ll ever have the persiverity to do as you suggest. Kudos to you for yours. As a shooter, I appreciate reading all and any information that researchers like yourself provide.

 

[justin amateur]

Being a touch OCD has it's uses.
I was frustrated by results from 17hmr and the chronograph numbers, ES almost 400 fps.
Another shooter had pulled a few apart and seen the differences in primer application.
I wondered how much. CCI still uses a punch plate and manually loads the plate to fill the brass.
Primer amounts varied, plus or minus 0.3 grains in the 50 dissected.

 

[trophyhunter]

I chrony 10rds at the end of the day to get a good base on my data for my kestrel. Of the 7 chrony (1039) I got SD of 6.5, ES of 13. I had 2 998-990 & 1 1051.

I don’t think I’ll take apart 50 to burn the powder but I am going to weigh, sort, then zero the rifle with the magnetospeed attached then shoot through my ShotMarker to see the results.

Will post findings shortly after