About the supersonic/subsonic transition...

[TruthTellers]

I know that as a .22 LR moves from being supersonic to subsonic down range it causes issues during flight leading to decrease in accuracy, but I am wondering does the transition have a detrimental effect on larger calibers or is the extra size and weight of those bullets enough to withstand the transition without any issues?

[Scorch]

All bullets going trans-sonic are affected, some more than others due to shape.

[TruthTellers]

Originally Posted by Scorch

All bullets going trans-sonic are affected, some more than others due to shape.

The bullet profile is a factor? I take it long and skinny ones are more affected than short, fat bullets?

That would be good because I'm wondering more about .40 or .45 caliber pistol bullets fired from carbines a bit over speed of sound, then going below it after 50 or 100 or 150 yards down range.

[fourbore]

It is also a question of "how much". I would need to do some research, I do not have an answer. But, if the "how much" was 1/4 moa, then on a 45 carbine you could never even see that. The Ruger KalTec stuff maybe 2-3 MOA guns. That maybe best case optimistic.

I shoot a lot of rimfire, I should know. But; I never did an experiment to measure the effect on 22LR. It could not be more than 1/2 moa. I guess, much less. My gut feel, is that it will not be significant on a pistol caliber semi carbine.

The Kaltec is on my long list and I would probably shoot 8" steel plates at 100 yards off hand. Ignorance is bliss.

[Jim Watson]

I doubt you will see an effect in a PCC.
Smallbore target shooters use subsonic .22 LR, it does matter to them.
A Long Range shooter will use high ballistic coefficient bullets to stay supersonic at the target.
BPCR shooters just put up with the transition, experiments in subsonics and attempts to cast boattail spitzers did not pay off.

[emcon5]

As I understand it, the issue is the shape of the boat tail. The example most long range shooters tend to be aware of is the Sierra .308 168gr MatchKing. With a 13º boat tail, it has a reputation for not handling the transition to subsonic very well, and is generally considered a 800 yard bullet. Other 168gr .308 bullets, like the Berger have a narrower boat tail angle, 7-9º and do not have the same issue.

More info here: http://bulletin.accurateshooter.com/...-and-accuracy/

[MarkCO]

A few points to ponder. First, transonic is not really a specific number, it is a range from 0.8 to 1.2 Mach. Second, a bullet from about .8 to 1.0 Mach will have air passing over it that is going over Mach. Consider what gives an airplane wing lift...same physics applies, but in 360 degrees. Third, the disruption magnifies the instability and it is compounding. While mass matters, sectional density seems to matter more practically.

As for PCCs, yes, it does have an affect, and I have been able to show it. Obviously, the less stability the bullet has from shape and spin, the greater the effect. While most .22LRs are 1:16 twist, there is data to suggest that 1:12 to 1:14 twist will give better accuracy out past 100 yards with subsonic ammo. The same is true of PCCs. Anyway, with 1300 fps or so 9mm, you go transonic just after 100 yards. My PCC shoots about 2 MOA out to about 10 yards past the transonic point (120 yards) then it starts to open up. 30 yards past transonic, I was up to 5 MOA and at 50 yards past transonic I was over 10 MOA (200 yards). Same exact bullet and PCC, started out at 950 fps (140 fps below transonic) I was getting a 4 MOA group at 200 yards. Granted I don't normally shoot my 9mm PCC with a Precision optic, bi-pods and bags, but I wanted to see what the practical limits of the 9mm PCC were for several ammo types and velocities. While I have a few loads I have been able to shoot out to 300 yards with good (4-5 MOA) accuracy, it is not practical nor is it fun. About 100 yards is, IMHO, the practical limit and with almost all PCCs and 9mm ammo combos, they should be 5-6 MOA capable at that distance, most better. But few combos can be expected to carry their 100 yard and in accuracy past 150 yards.

[Scorch]

As I understand it, the issue is the shape of the boat tail

The issue is the collapse of the shock wave created by objects at supersonic speeds. As a supersonic bullet slows down to the speed of sound, the shape of the shock wave changes. As the edges of the shock wave get closer to the projectile, the projectile is destabilized in flight. As the shock wave touches the projectile, the projectile's flight is upset and it will tumble in flight. There have been many, many experiments trying to develop a bullet that is stable in trans-sonic flight, and many "ideal" shapes developed that did not work out. Remember the to-do about truncated cones in the early 1980s and double angle boat-tails in the 1970s?

Consider what gives an airplane wing lift...same physics applies

No. Just no. Bullets are symmetrical, so they do not generate lift. That comes from cambered airfoils.

[emcon5]

The issue is the collapse of the shock wave created by objects at supersonic speeds.

OK, but the influence the shock wave has on the stability in transonic flight is affected by the shape of the bullet.

Can you find any reference that says the destabilization of Sierra 168 Matchkings when they drop subsonic is anything other than the shape of the boat tail?

No. Just no. Bullets are symmetrical, so they do not generate lift. That comes from cambered airfoils.

That is not what he said. He said "Second, a bullet from about .8 to 1.0 Mach will have air passing over it that is going over Mach. Consider what gives an airplane wing lift...same physics applies, but in 360 degrees."

And he is right. The shape of the bullet does cause air to pass over the surface of the bullet at a speed faster than the bullet is traveling, which is exactly the same physics of air traveling over the top of a wing creating lift.

Nowhere in there did he say bullets generate lift.

[TXAZ]

Higher BC and bullet weight (with all other variables and shapes being the same, and they never are) will have a significantly longer flight time before hitting transonic, assuming similar muzzle velocity.
A .50 BMG Hornady 750gr match won't go transonic till it gets out to 1.5 to 2 miles depending on the barrel and environment.

A .22 LR is likely transonic within 400 yards.

[davidsog]

Normal shock most certainly influences the path of a bullet.

https://pdfs.semanticscholar.org/f2c...2578caeae9.pdf

I am wondering does the transition have a detrimental effect on larger calibers or is the extra size and weight of those bullets enough to withstand the transition without any issues?

No, the influence of normal shock is independent of size and weight. Normal shock formation even influences things as large as the Saturn V rockets, SR-71, and any object that moves fast enough for normal shock formation.

[MarkCO]

Scorch, quote clip to make an errant judgement much? I said

Consider what gives an airplane wing lift...same physics applies, but in 360 degrees

Which is absolutely true as to the the airspeed and Mach. Shock waves don't collapse either and the edges, in supersonic flight are NEVER even remotely close to the base. They are only at the tip, "touching". Sure, there are other affects, but your explanation is not even remotely close to reality. Hundreds of hours in wind tunnels measuring and categorizing Mach numbers gives me a little inside edge maybe.

Mach is not the only issue. Sure Mach is a profound affect in the transition phase and form factors interplay, but the movement of air over surfaces is a big deal. It is what sheds the speed and causes us to have to compensate for other than a straight line with a constant slope. It is rather a curve with variables that are functions of each other. Some of the "math" that is done on your smart phones in the ballistic apps took me days to run on a Cray computer in the 1980s, and took months of hand calculations in the 1960s. Turbulence and laminar flow are in a constant state of change for any object moving through a medium. We affect those by shapes; angles and curves. Messing them up with a ring above the ogive from a seating die, or shaving off jacket due to a tight case neck that is not chamfered thus have a detrimental affect on not just the consistency, but the actual flight path of the bullet. Why flyers are such an issue...was it the shooter, or the loader.

[davidsog]

Shock waves ..........and the edges, in supersonic flight are NEVER even remotely close to the base.

You seem to be confusing the behavior of the Bow wave with normal shock or I am not understanding exactly what you are trying to say in the mechanics of this statement.

Normal Shock moves up and down a body in flight.

In aircraft, it is the movement of normal shock that causes compressibility, mach tuck, and other effects upon stability and control just like a bullet in flight.

In fact, "breaking the sound barrier" is the defined by the body passing thru the normal shock. That means the normal shock has passed the ends of the body in flight.

[MarkCO]

You are right davidsog, trying to oversimplify with what is practically significant and I did not do a good job. There are differences as to how each affects stability.

[Don Fischer]

I have read that the biggest problem with cartridge's for 1000 yd shooting is the inability of the bullet to stay super sonic. I can buy that. Get a top and spin it on the floor. As it slows down it start's to wobble. That I would think is about what happens when a bullet falls below super sonic. A wobbling bullet can't be very accurate!

[davidsog]

Thanks MarkCO. I was not sure if I just misunderstood the way you wrote it or the concept was wrong.

Given that you stated you are working in a windtunnel I tended to think I just misunderstood you.

Found a good photo of a bullet in flight that nicely illustrates the normal shock of supersonic flight.

[BeeShooter]

The properties of air changes as it moves in supersonic speeds and subsonic speeds. Air flow is considered compressible at sonic and supersonic speeds. The Opposite is true. Air flow is considered to be not compressible below sonic speeds( subsonic). This obviously is referring to relative airflow, lol. As the bullet, a conical shaped object of sorts, has its relative air flow transition into subsonic speeds the flow of air around the bullet will affect it more. The weight, shape and stabilizing spin is needed most when this happens. Long range shooters try their best to keep the bullet above supersonic for as long as possible but when the speed falls off the manufacturing quality and design of the bullet is about the only thing you've got going for you.

[davidsog]

As the shock wave touches the projectile, the projectile's flight is upset and it will tumble in flight.

This is the part causing contention and why MarkCO replied correctly.

Boundary layer mechanics dictate the normal shock will never touch a body in flight.

The influence of normal shock on a body in flight are caused by the characteristics of normal shock.

All of these effects are the result of what is called force divergence. As normal shock forms, the air in front of the shock is supersonic while the air behind the normal shock is subsonic.

This causes the boundary layer to seperate from the body in flight changing our force relationship about the Center of Gravity of a body in flight. Think of it like there is a vacuum formed right behind that normal shock line in the photo. There is nothing to push against in a vacuum.

The body in flight always attempts to move those forces to balance resulting in moments about the Center of Gravity causing your bullet flight path to change.

[Erno86]

Originally Posted by Scorch

No. Just no. Bullets are symmetrical, so they do not generate lift.

I agree to disagree...

Bullets fired from a right hand twisted barrel, will generate lift in a right to left wind --- And vice versa --- With a right hand twisted barrel causing the bullet to travel downward in a left to right wind.

[MarkCO]

^ Aerodynamic jump. I account for it past about 800 or so.

[PlatinumCore16]

Gosh that was a beautiful conversation to read through. As a small aside, the spinning effect can actually work in real case scenarios and experimental airplanes have been flown that way, though not terribly effectively.

On the subject of all of the various bullet designs considered for transsonic regime, was there ever any experimentation done with forcing turbulent boundary layer flow, a la dimples/shot peened cases in the back half/last 1/3 of the bullet? Or any more airfoil-shaped bullets to perhaps not do so well in supersonic, but yet maintain momentum through the transsonic regime?

[MarkCO]

I tried modeling some dimpled designs for a project in the 1990s. I used a random pattern and sizing akin to a golf ball. It did not work for supersonic in the model, but I did not spend much time on it and my graduate advisor thought it was stupid.

Later, working on a different project, we were able to extend the range of dimpled steel balls that were propelled at about 3,000 fps, but there was no rifling.

I am sure there are some things that are possible, but not practical given current components. When poly cases become a thing, some of those might come to light.

[Jim Watson]

Or any more airfoil-shaped bullets to perhaps not do so well in supersonic, but yet maintain momentum through the transsonic regime?

Like the Krnka-Hebler tubular bullet?

[PlatinumCore16]

Had no idea that was a thing. Thank you for that. Though it's more of an attempt to extend the supersonic speed out by a large factor, so similar end goal.

[davidsog]

Or any more airfoil-shaped bullets to perhaps not do so well in supersonic, but yet maintain momentum through the transsonic regime?

A boat-tail bullet takes advantage of the characteristics of the expansion wave just like a supercritical airfoil.