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Discussion Starter · #1 ·
Does anyone have experience with handguns bullet velocity going supersonic to subsonic and its effect on accuracy?
For example if my muzzle speed is just over the speed of sound but by the time it reaches 25 yards it is subsonic will my accuracy be erratic?
 

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I don't have the equipment to test what I have learned about bullets transitioning from subsonic to supersonic or the reverse. I base my thoughts on this on the problems airplanes had going to supersonic speeds in the 1940s. There is a shock wave that buffets the moving object and it causes vibration and more shaking than a 50s rock and roll singer. That can't be good for accuracy.


s
Harold Mendelson
 

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I have never worried about this concept and don't plan on starting. The biggest accuracy problem I have with handguns is operator error.
 

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rorshach1980, Sonic transition is the biggest farce since the tooth fairy. Some people think when a bullet transitions from supersonic to sub sonic (about 1100 fps) all of a sudden the bullet goes crazy and accuracy goes down the tubes. Fact is, sonic transition in it's worst case scenario is nothing more than a slight "bump in the road" that has virtually no affect on accuracy.

Light small diameter bullets are affected more by sonic transition than heavier and larger diameter bullets, because heavier bullets have better gyro stability. Worst case would be a light 22 LR with a very poor ballistic coefficient (BC). A 40gr HV 22 LR leaves the muzzle at about 1250 fps and at about 30~35 yards, it slows down to 1100 fps and transitions to subsonic. I think we all know ... a 22 LR can be very accurate out to 100 yards or more ... 65~70 yards AFTER it went through sonic transition.

Handgun bullets typically have a poor BC, meaning air friction slows them down pretty fast. One of the worst case examples is a factory load 115gr 9mm FMJ bullet that leaves the muzzle at 1155 fps and goes sub sonic before it reaches 20 yards. Again, I think we all know a light 115gr 9mm bullet will maintain stability out to 100 yards or more. BTW, 9mm pistols have about the fastest twist rate of any handgun .... 1:10, whereas a 38 Special/357 Mag has a slow TW of 1:18.75

How can you tell when a bullet becomes unstable? If you examine your paper target and experiment at different distances, you will see holes get oval shaped as bullets start to yaw. Soon after, bullets will begin to tumble and will create "keyholes" in the paper target. The distance where you first see oval holes is called the point of instability.

This sonic transition "theory" started back in the 1960's when the military went to M-16 rifles that initially had a twist rate of 1:12 and fired a 55gr FMJ with a very poor BC of .103. Turns out, bullets would become unstable and start to tumble at about 250 yards and by 300 yards, every bullet was printing keyholes in the paper target. By coincidence, bullets went through sonic transition at about 250 yards so someone came up with the wild idea that it was sonic transition that caused bullets to become unstable. Of course this story spread like wildfire and here we are 50 years later where the fairy tale is still believed to be gospel. Funny thing .... when the military later changed the twist rate in M-16s to 1:10, the same exact 55gr FMJ ammo would maintain stability to about 400 yards, yet when it was chronographed at 250 yards, it was still 1100 fps ... the same as when the twist rate was 1:12. Of course the general public never connected the dots. What does this tell you? It tells me the sonic transition theory is a bunch of crap.

In more recent years, high speed video photography has been able to capture pictures of bullets going through sonic transition. In these pictures, lighter bullets experience a slight "bump" then recover back to their normal flight path. With heavier and larger diameter bullets, there is no visible "bump" at sonic transition.
 

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Discussion Starter · #6 ·
Sounds about right to me. I was just wondering if it would affect my load that is 1070ish from my 4 5/8 vaquero, and around 1200ish from my 7.5" super blackhawk. I was worried it would only be accurate from the sbh out to whatever distance it went transonic then drop off.
I agree that whatever difference it would move the bullet wouldnt be enough to affect accuracy at the distances a handgun is fired, no more than shooter error anyway. Now if i were shooting 1000 yards with it and it went transonic at 25 yards then it may have an effect, but im not good enough that i would notice it anyway.
I think i was just overthinking a problem i dont really have. Haha. Thanks!
 

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Forgetting some physics knowledge I knew in the past I did some research to relearn the principles of the effects of objects going into transonic speeds from .8 mach to 1.2 to 1.3 mach.
Here is what happens there are three effects that change. In no particular order: the drag on an object increases during transonic flight. There are shock waves created. One above the object and one below it. These shock waves move toward the rear of the object. These shock waves effect the air flow going around the object. The two shock waves move at different rates across the object. As the object increases in speed these shock waves eventually meet at the end of the object. At about that time, another shock wave forms in front of the object until the object increases its speed and passes through the transonic speed zone. All of these shock waves create effects that changes the object's BC and causes buffering which in the case of a bullet to increase its yaw. The degree of this effects depends on the shape of the bullet.
For an example take a 168 gr .308 match king. With a MV of 2,800 fps goes transonic at about 750 meters. The bullets begins to yaw and by the time it reaches 1,000 yards the bullet will either be tawing violently or moving base first. Looking at the bullet impacts on the target confirm this. As I said in my earlier post, most match Shooters either move to a different bullet and or increase the MV so it does not go transonic until after it reaches the target.
Conversely, match pistol shooters keep the MV of their rounds below transonic speeds to prevent these shock waves from forming.
On another related topic, using Doppler radar it was determined that the recent use of synthetic tips and the old exposed lead Spitzer created a problem. It was determined that the temperature at the tip of the bullet was reaching 900 degrees causing the bullet tips to deform resulting in lost stability.
 

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hmendelson1946, Your explanations is exactly what I was trying to debunk. I don't doubt all that rhetoric happens ... and let's assume it does. The bottom line is ... did it affect the accuracy of the bullet within its usable range? Better yet, if it did affect the bullet's accuracy, how far downrange did this happen?

One of the classic experiments involves a 223 Rem cartridge, 55gr FMJ .224 bullets because they have a grim BC ... less than .200 in the book, about .150 in actual tests. The muzzle velocity is 3240 fps from a bolt action 24" barrel, 1:12 TR. These bullets go subsonic at about 300 yards and by 350 yards, the bullets are flipping end over end. This would make a person think it was sonic transition that caused this event. Take the same exact ammo and fire it from a faster twist barrel ... ie a AR-15 with a 1:9 TR 20" barrel at 3100 fps. Turns out this bullet will go subsonic at about 260 yards ... 40 yards sooner because MV was lower. Strange thing is ... the bullet now maintains stability and good accuracy to more than 400 yards. If sonic transition is so dramatic, why does this little bullet stay stable more than 150 yards after passing through sonic transition???

Let's apply some more practical applications. Typical bullets used for hunting big game have lower BCs than bullets used for long range target shooting. A typical hunting bullet from most any high power rifle will maintain stability well past it's effective hunting range. Using a 30-'06 as an example with a 180gr bullet (BC=.350) fired at 2700 fps, it will go subsonic at 450 yards. So assuming the bullet goes totally crazy when it passes through sonic transition, the effective stability range still exceeds the effective hunting distance by about 200 yards.

Lets take another 30'06 cartridge only this time let's use a 168gr match bullet with a BC of .600. It will travel 730 yards before it goes through sonic transition. In a 300 Win Mag rifle, the same bullet can go in excess of 1000 yards before it transitions to subsonic. Guys, that's a LONG ways and so what if the bullet gets upset at sonic transition ... it is still farther than most shooters will ever experience.

A typical 22 LR bullet has a very poor BC, a slow twist rate (1:16) and a MV of about 1250 fps ... a combination of all the poor attributes. It will go through sonic transition at about 30 yards but will still be quite accurate well past 100 yards.

The point of the sonic transition concept being ... just because a bullet goes subsonic, it doesn't mean it will turn crazy and do wild things ... in fact it will likely remain stable for a considerable distance downrange before the spin rate decays and it loses stability. The second point is ... even if a bullet went nuts after sonic transition, it is far enough downrange where it really doesn't matter. Bottom line ... sonic transition is way more of a farce than a fact!
 
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Very nice explanation Iowegan. The .22lr part really brings it into focus, as I have shot excellent groups with Standard Velocity CCI ammo.

I experimented with reloading some subsonic .223 Rem. loads with about 3.1 grains of TiteGroup under a 55 grain Hornady FMJBT bullet, at about 1,075 fps.

It shot a very nice group at 50 yards & it was very quiet, but the group was about 1.5 to 2" below POA.
 

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I just do not buy into the idea of transonic bullets tumbling after transition to subsonic. At least not on a general basis. The spin of the bullet does slow but not as much as velocity or as rapidly. So I have read on several occasions. I would not argue maybe some temporary instability but a 308 goes base forward after 750 meters I would have to see that for myself to believe it. The 308 has been used for long range competition and sniping for a long time and I have to believe if instability with that weight bullet was reality that would not be the case.

Theories make great discussion topics but what I am reading here is not as I have experienced particularly with the 223 and 1:12 barrels of larger calibers. I will need more than ideas before I believe this.
 

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Discussion Starter · #11 ·
Sort of like spin drift, it does make a difference but it is so minute you can't notice it until long range is reached. Even at 1000 yards its maybe 1 click if that.
 

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Here is more proof! I from time to time will shoot my 475 ,44 and 41 out to 500 yds.
My 475 chronos at 1420 avg at 10 ft from the muzzle I am still able to reliably hit a 20"x 20" target with no keying and I am running a 400 gn LBT wide flat nose that basically no BC. I dont buy the transition theory either
 

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twodog max,
The spin of the bullet does slow but not as much as velocity or as rapidly.
This one will fool you ... bullet spin rate does decay proportional to velocity loss. It's a simple concept ... air friction slows the velocity of the bullet and at the same time, air friction will also slow the bullet's spin rate by a proportional amount. The bullet's ballistic coefficient will dictate both velocity loss and spin rate loss. You can actually compute the approximate downrange bullet spin if you know muzzle velocity and downrange velocity. For openers, a bullet's spin is based on the barrel's twist rate and velocity. Here's the formula: Spin rate (in RPM) = velocity (in fps) times 12, divided by twist rate, times 60. So let's say you had a bullet exiting the muzzle at 3000 fps with a twist rate of 1:9 ..... 3000*12=36,000/9=4000x60=240,000 rpm. Lets also say you chronographed this bullet downrange and found it had a retained velocity of 2000 fps. So at the downrange location, bullet spin will be about 160,000 rpm. Here's the math: 2000/3000=.6666; 240,000 * .6666 = 160,000 rpm. A bullet with a higher BC will maintain higher retained velocity farther downrange .... so it will also retain a higher bullet spin rate.

As it turns out in 99% of the cases, the reason why a bullet becomes unstable and starts tumbling is because the spin rate drops below the threshold of gyro stability .... not because of sonic transition. Bullets are naturally unstable because the nose is lighter than the base so once the spin rate decays, the base wants to swap ends with the nose. As soon as the bullet starts to yaw (nose pointed in some direction other than straight forward) air friction will increase radically and slow the bullet more. The nose of the bullet reacts by yawing even more ... the cycle continues until yaw get so extreme ... the bullet begins to tumble. A few things influence the point where the spin rate doesn't support the gyro effect ... mostly bullet damage or just an imperfect bullet to begin with. Match grade bullets are as perfect as possible and will maintain stability much farther downrange than a normal bullet with the same weight and diameter. Bulk grade bullets are typically the worst and may become unstable at much closer distances.

Every bullet has a specific gyro stability RPM. In other words, the minimum RPM necessary to keep it stable. Once RPMs decay below the point of gyro stability, the bullet will begin to yaw and tumble. The larger the diameter of the bullet, the less RPMs it takes to keep it stable in flight. Likewise, small diameter bullets like those used in a 223 Rem, have to be spun super fast to maintain stability .... worst case would be 17 cal bullets. This is why you see small bore rifles with very fast twist rates coupled with very fast muzzle velocities and is also why you see very slow twist rates at lower velocities in large caliber guns. This concept explains why 475linebaugh can shoot those fat 40+ cal bullets out to 500 yards without losing stability. As I pointed out in my above post, don't lose sleep over bullet stability .... chances are you will never out shoot your bullet's stability range.
 

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Sounds about right to me. I was just wondering if it would affect my load that is 1070ish from my 4 5/8 vaquero, and around 1200ish from my 7.5" super blackhawk. I was worried it would only be accurate from the sbh out to whatever distance it went transonic then drop off.
I agree that whatever difference it would move the bullet wouldnt be enough to affect accuracy at the distances a handgun is fired, no more than shooter error anyway. Now if i were shooting 1000 yards with it and it went transonic at 25 yards then it may have an effect, but im not good enough that i would notice it anyway.
I think i was just overthinking a problem i dont really have. Haha. Thanks!
Yes, you're over-thinking this. At 1070 and 1200, you're already within the transonic boundary.

Guys shoot through transonic boundary every day with handguns.
 

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This one will fool you ... bullet spin rate does decay proportional to velocity loss. It's a simple concept ... air friction slows the velocity of the bullet and at the same time, air friction will also slow the bullet's spin rate by a proportional amount. The bullet's ballistic coefficient will dictate both velocity loss and spin rate loss. You can actually compute the approximate downrange bullet spin if you know muzzle velocity and downrange velocity. For openers, a bullet's spin is based on the barrel's twist rate and velocity. Here's the formula: Spin rate (in RPM) = velocity (in fps) times 12, divided by twist rate, times 60. So let's say you had a bullet exiting the muzzle at 3000 fps with a twist rate of 1:9 ..... 3000*12=36,000/9=4000x60=240,000 rpm. Lets also say you chronographed this bullet downrange and found it had a retained velocity of 2000 fps. So at the downrange location, bullet spin will be about 160,000 rpm. Here's the math: 2000/3000=.6666; 240,000 * .6666 = 160,000 rpm. A bullet with a higher BC will maintain higher retained velocity farther downrange .... so it will also retain a higher bullet spin rate.
I can't really divulge the method of the testing, but the US Navy has evidence to disagree with the mathematics that you provided above, I took part in that particular project. Wasn't done with small arms, as you might expect for a Navy project, but ballistics (physics) doesn't really care if it's a 22cal bullet or a 105mm.

Yes, there is drag/resistance that slows the spin of the bullet over time, but it's not proportionate to the bullet's air speed.

Long story short, you cannot take twist rate of your bore times the velocity at range to get the RPM at that point.

There's a lot of detail and mathematics behind it, which ends up being remarkably simple once it's all worked out, but the rotational spin resistance and linear flight resistance forces are linked, but NOT directly proportionate. The drag force against the bullet spin is based on the vector of directional air flow parallel to the rotating surface. The drag force on the bullet in flight is based on the air speed. The rotational resistance is actually decreased by boundary layer shedding as the bullet moves through the air linearly (roughly). As the bullet slows, the rotational resistance does increase, since the boundary layer is not shed as rapidly. The empirical - read "Real world" testing done in the project cited above confirmed the mathematics to a tee.
 

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Varminterror,
ballistics (physics) doesn't really care if it's a 22cal bullet or a 105mm.
Yes it does care!. I certainly don't have a way to measure downrange bullet spin ... just going by published articles that date back 20 years. FYI, there is a huge difference comparing a small arms bullet with an artillery projectile. As you know, diameter and weight have a huge impact on gyro effect and spin decay ... as such the scale of distance would be proportional to the scale of weight and diameter. In other words, a 105mm projectile verses a 7mm bullet ... the projectile is 15 times larger in diameter, however the big difference is in weight where a 7mm bullet is 150gr, a 105mm projectile way disproportionate. I would guess it would be many miles for a projectile ... versus 100 yards for a 7mm bullet to achieve the same percent of spin rate decay. In other words ... just not a fair comparison. If you could scale up a 7mm bullet to 105mm, the weight would be 2250gr or about .32 lb. I have no clue what a 105mm projectile weighs ... 20lbs ... 30lbs?? but what ever it is it's a heck of a lot more than .32 lbs.
 

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I'm not interested in arguing this. You can pick apart one comment, but the point of my response is still true - spin rate does NOT decay equivalent to velocity, and I assure you, the research exists to prove it AND to prove that it applies whether the projectile is measured in pounds or grains. Old dogs can learn new tricks, and the 20yr old papers you reference were proven wrong in the early 2000's by the project in which I participated. We did the preliminary research with "guns," millions of dollars of equipment, and confirmed it for small arms thereafter. Again, the spin rate vs. air speed is NOT linked in the ratio that you mentioned (twist rate x velocity at range = rpm is NOT applicable at range). Folks a lot smarter and more experienced than you or I set up the testing, and what came out was a remarkable realization of how simple it really is.

Call the State Department in 20-50yrs, in general that's about how long it takes for this type of research to become public, although I'd venture that some private firm may replicate the same research in that time (not so uncertain that Hornady's testing for their new heat-proof tips wasn't the same equipment).
 

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Regardless of the final outcome of this discussion, I find it very interesting.

Thanks to all who have contributed.
 

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FWIW, the aerodynamic moment related to roll (spin) damping is typically expressed as:

Lp = ( Q*S*D*D/(2*V)*CLp*p

Then, assuming a roll symmetric projectile with a diagonal inertia tensor, the spin angular deceleration (pdot) due to this moment is:
pdot = Lp/(Ixx) = ( Q*S*D*D/(2*V*Ixx)*CLp*p

where,
p is the spin rate
V is the projectile velocity
Q is the dynamic pressure = .5*air_density*velocity_squared
Clp is the normalized roll rate stability derivative
Ixx is the roll inertia of the bullet
S is the reference area
D is the reference length (typically the bullet diameter)

So, in terms of the dynamic variables, it looks like the roll deceleration (i.e., time rate of change of the roll rate) is proportional to the product of velocity*roll rate.
 
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