New Transonically Stable 308 Bullet

[Buffalobob]

Berger has designed and tested a new 308 bullet that will pass through the transonic zone without being upset. It is not yet listed on their website but is in the production line. Bryan Litz, the ballistician for Berger has loaded ammo listed for sale on his website. It may have some interesting applications for the military in terms of extending the range of the 308 sniper rifles.

Here is the link

http://www.appliedballisticsllc.com/TacticalAmmo.html

[Sinister]

Interesting. Nowhere in that page do they indicate what their muzzle velocity is out of the 20-inch OBR.

[Buffalobob]

You should duly note that it is not ammo loaded by Berger. It is loaded by Bryan who keeps his personal company even while an employee of Berger.

I would suspect it is not loaded to any extreme velocity for insurance liability reasons. I would imagine out of a 20 inch barrel you could get 2500 to 2550 fps depending on lots of factors.

[mojaveman]

Does barrel length and rifling have much affect on transonically stabilizing a bullet? I have a friend who builds custom tactical rifles and he made one with a barrel that was about three feet long. He was trying to explain it all to me but I was in a hurry that day and I didn't quite get all of it. Just curious.

[Brush Okie]

Originally Posted by Buffalobob

You should duly note that it is not ammo loaded by Berger. It is loaded by Bryan who keeps his personal company even while an employee of Berger.

I would suspect it is not loaded to any extreme velocity for insurance liability reasons. I would imagine out of a 20 inch barrel you could get 2500 to 2550 fps depending on lots of factors.

Some tests done a few years ago found that there is very little to no velocity loss out of a 20 in barrel for a .308 depending on the powder. Here is a link to an article I found using my google-fu

http://www.tacticaloperations.com/SWATbarrel/

And and except from the article.

There isn't any clear-cut answer as to how much velocity will be lost per inch of barrel length reduction. The amount of loss is closely tied to the expansion ratio. As previously noted, the type and amount of powder, as well as the weight and bearing length of the bullet, also play a major part. Rifles with high expansion ratios (smaller calibers) tend to lose less velocity than rifles with low expansion ratios (larger calibers).

Tactical Operations about in the April 2000 issue of S.W.A.T., typifies the trend to rifles with shorter barrels. Tac Ops considers a barrel of length of 18 to 20 inches to be optimal for the urban environment, with 18 inches the preferred length.

During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each invrement. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps). Shorter barreled rifles are more versatile, being equally suitable for both urban and rural operations. According to Tac Ops, there isn't any need to go to the 26-inch barrel unless you want to go to a heavier bullet or push the round to higher velocity using more powder or use a slower burning powder. The Los Angeles County Sheriff's Department's Special Enforcement Bureau (SEB) performed tests similar to those conducted by Tac Ops and came to similar conclusions.

[Brush Okie]

Originally Posted by mojaveman

Does barrel length and rifling have much affect on transonically stabilizing a bullet? I have a friend who builds custom tactical rifles and he made one with a barrel that was about three feet long. He was trying to explain it all to me but I was in a hurry that day and I didn't quite get all of it. Just curious.

When a bullet drops below the sound barrier it tends to destabilize and accuracy suffers. That is why a .22 long rifle match ammo is subsonic.

[mojaveman]

Originally Posted by Brush Okie

Some tests done a few years ago found that there is very little to no velocity loss out of a 20 in barrel for a .308 depending on the powder. Here is a link to an article I found using my google-fu

http://www.tacticaloperations.com/SWATbarrel/

And and except from the article.

That would equate to about 4FPS for each inch of barrel length lost.

[Buffalobob]

Does barrel length and rifling have much affect on transonically stabilizing a bullet? I have a friend who builds custom tactical rifles and he made one with a barrel that was about three feet long. He was trying to explain it all to me but I was in a hurry that day and I didn't quite get all of it. Just curious.

Most serious 1K competitors using the 308 will use a 28-30 inch barrel. They will hand load their own ammunition and will push pressures as high as they can without affecting group size. The idea is to achieve high velocity to minimize wind drift and drop variations and to stay above Mach 1.2.

Barrel twist is not especially important to transonic stability above and beyond regular stability concerns. Bullet shape is important. Shallow boat tail angle and no meplat or very small meplat, and short bearing surface seem to be important. Interestingly, the old black powder buffalo sharps aficionados shoot cast lead bullets very accurately far beyond the transonic zone.

As far as the Swat study I have not shot any factory loaded rifle ammo in three decades so I just don't have any knowledge base concerning burning rates of the powder used.

[Brush Okie]

Originally Posted by Buffalobob

Most serious 1K competitors using the 308 will use a 28-30 inch barrel. They will hand load their own ammunition and will push pressures as high as they can without affecting group size. The idea is to achieve high velocity to minimize wind drift and drop variations and to stay above Mach 1.2.

Barrel twist is not especially important to transonic stability above and beyond regular stability concerns. Bullet shape is important. Shallow boat tail angle and no meplat or very small meplat, and short bearing surface seem to be important. Interestingly, the old black powder buffalo sharps aficionados shoot cast lead bullets very accurately far beyond the transonic zone.

As far as the Swat study I have not shot any factory loaded rifle ammo in three decades so I just don't have any knowledge base concerning burning rates of the powder used.

The palma shooters use a 155 gr plama bullet not sure what bullet they use. also they are using metallic sights so the longer sight radius is a big benefit as well. The 308 is no longer used by serious 1000 yard shooters these days. The 6.5 bullets and the 6.5x284 seems to be the favorite. Completly diffret set of rules. The 20 in bbl pertains to 308 with specific powders only. Change variables ie powder, caliber etc etc everything changes.

[Buffalobob]

The 308 is no longer used by serious 1000 yard shooters these days.

I assume from your statement that you have never actually done any competition shooting at long range. There is a whole group of F-class called F-T/R which includes only 308 and 223 (military calibers ). It is what I shoot and what I trained my children to shoot. I have posted several videos of my children shooting in long range F-class with a Rem 40X in 308. The 6.5-284 competes in a class called "open" which is not head to head with the 308.

Do you actually know anything about bullets and the transonic zone and killing people?

[Brush Okie]

Originally Posted by Buffalobob

IDo you actually know anything about bullets and the transonic zone and killing people?

Yes I do. but Im not going to get into an argument on the internet.

[incarcerated]

Originally Posted by Buffalobob

Bullet shape is important. Shallow boat tail angle and no meplat or very small meplat, and short bearing surface seem to be important.

Ahhhh…
I can see the meplat being an issue, as a hollow point degrades the BC of any rifle bullet, but I had not considered the boat tail. If the instability derives from changes in the bullet’s shockwave as it crosses the transonic plane, which was my uneducated guess (and which turns out to be not quite accurate), my attention would be on the front of the bullet. Being a short-range shooter (nothing much past 200) and fond of flat base bullets, I would not have considered the effect of the vortex following the bullet. The short bearing surface will help at both ends of the bullet, or put differently, will result from reducing bluntness up front and lengthening the taper of the boat tail.
Will an epoxy filled nose and a rearward center of gravity help things here?
And where is Longrange1947? I’d like to hear his input on this.

A little Google-fu helped throw some light on the issue for me: rather than looking at the bullet, it got me looking at aerodynamics, specifically, the transonic zone:

http://answers.yahoo.com/question/in...3211733AA9JEeY
The Transonic zone is a condition of speed when some parts of the air flowing over an object, such as an airfoil are supersonic already and some parts are not. The term to watch between the transonic zone and the supersonic zone is called the Critical Mach number...where the airlow in some parts of an object, again, the typical example would be an airfoil..reaches the speed of sound, even though other parts of the aircraft has not crashed through the sound barrier. When this condition is reached, it will create a weak shock wave.

A shock wave is a condition where a there is always a rapid rise in pressure, density and temperature. As the aircraft approaches the transonic zone--Mach .80 to Mach 1.2--the pressure waves do not have time to move out of the way of the oncoming aircraft since it is traveling along with them. The waves compress and the air becomes far more dense. When the plane meets the compacted air, it hits with a jolt and a series of shock waves builds up perpendicular to the direction of flight. The first shock wave attaches itself to the center of the wing's upper surface as the airflow there reaches Mach 1, As the plane's speed increases, the air under the wing also reaches mach 1 and a second shock wave forms....

http://www.centennialofflight.gov/es..._Flow/TH19.htm
An airplane flying well below the speed of sound creates a disturbance in the air and sends out pressure pulses in all directions. Air ahead of the airplane receives these "messages" before the airplane arrives and the flow separates around the airplane. But as the plane approaches the speed of sound, the pressure pulses merge closer and closer together in front of the airplane and little time elapses between the time the air gets a warning of the plane's approach and the plane's actual arrival time. At the speed of sound, the pressure pulses move at the same speed as the plane. They merge ahead of the airplane into a "shock wave" that is an almost instantaneous line of change in pressure, temperature, and density. The air has no warning of the approach of the airplane and abruptly passes through the shock system. There is a tendency for the air to break away from the airplane and not flow smoothly about it; as a result, there is a change in the aerodynamic forces from those experienced at low incompressible flow speeds….
At subsonic speeds, drag was composed of three main components—skin-friction drag, pressure drag, and induced drag (or drag due to lift). At transonic and supersonic speeds, there is a substantial increase in the total drag of the airplane due to fundamental changes in the pressure distribution.
This drag increase encountered at these high speeds is called wave drag. The drag of the airplane wing, or for that matter, any part of the airplane rises sharply, and large increases in thrust are necessary to obtain further increases in speed. This wave drag is due to the unstable formation of shock waves that transforms a considerable part of the available propulsive energy into heat, and to the induced separation of the flow from the airplane surfaces. Throughout the transonic range, the drag coefficient of the airplane is greater than in the supersonic range because of the erratic shock formation and general flow instabilities. Once a supersonic flow has been established, however, the flow stabilizes and the drag coefficient is reduced…

It is a large loss in propulsive energy due to the formation of shocks that causes wave drag. Up to a free-stream Mach number of about 0.7 to 0.8, compressibility effects have only minor effects on the flow pattern and drag. The flow is subsonic everywhere. As the flow must speed up as it proceeds about the airfoil, the local Mach number at the airfoil surface will be higher than the free-stream Mach number. There eventually occurs a free-stream Mach number called the critical Mach number at which a supersonic point appears somewhere on the airfoil surface, usually near the point of maximum thickness, and indicates that the flow at that point has reached Mach 1. As the free-stream Mach number is increased beyond the critical Mach number and approaches Mach 1, larger and larger regions of supersonic flow appear on the airfoil surface. In order for this supersonic flow to return to subsonic flow, it must pass through a shock (pressure discontinuity). This loss of velocity is accompanied by an increase in temperature, that is, a production of heat. This heat represents an expenditure of propulsive energy that may be presented as wave drag. These shocks appear anywhere on the airplane (wing, fuselage, engine nacelles, etc.) where, due to curvature and thickness, the localized Mach number exceeds 1.0 and the airflow must decelerate below the speed of sound. For transonic flow, the wave drag increase is greater than would be estimated from a loss of energy through the shock. In fact, the shock wave interacts with the boundary layer so that a separation of the boundary layer occurs immediately behind the shock. This condition accounts for a large increase in drag that is known as shock-induced (boundary-layer) separation….

At a free-stream Mach number greater than 1, a bow shock appears around the airfoil nose. Most of the airfoil is in supersonic flow. The flow begins to realign itself parallel to the body surface and stabilize, and the shock-induced separation is reduced.
This condition results in lower drag coefficients. Supersonic flow is better behaved than transonic flow and there are adequate theories that can predict the aerodynamic forces and moments present. Often, in transonic flow, the flow is unsteady, and the shock waves on the body surface may jump back and forth along the surface, thus disrupting and separating the flow over the wing surface. This sends pulsing, unsteady flow back to the tail surfaces of the airplane. The result is that the pilot feels a buffeting and vibration of both wing and tail controls. This condition occurred especially in the first airplane types to probe the sound barrier....

[Brush Okie]

Originally Posted by incarcerated

Ahhhh…
I can see the meplat being an issue, as a hollow point degrades the BC of any rifle bullet, but I had not considered the boat tail. If the instability derives from changes in the bullet’s shockwave as it crosses the transonic plane, which was my uneducated guess (and which turns out to be not quite accurate), my attention would be on the front of the bullet. Being a short-range shooter (nothing much past 200) and fond of flat base bullets, I would not have considered the effect of the vortex following the bullet. The short bearing surface will help at both ends of the bullet, or put differently, will result from reducing bluntness up front and lengthening the taper of the boat tail.
Will an epoxy filled nose and a rearward center of gravity help things here?
And where is Longrange1947? I’d like to hear his input on this.

A little Google-fu helped throw some light on the issue for me: rather than looking at the bullet, it got me looking at aerodynamics, specifically, the transonic zone:

There are lots of facters that affect the bullet shape of nose, etc etc. The boat tail bullet when designed was thought and still does reduce yaw when the bullet drops below supersonic. BTW there are lots of idea and theries in shooting and it is NOT an exact science so lots of umm heated discussion can happen even between experts. Basicly look at what the coefficant of a bullet. It is not even that simple since the BC of a bullet changes depending on velocity hence the Sierra manual gives BC for their bullets at diffrent velocity ranges. All else being equal heavier bullets tend to retain velocity better so at the muzzel a light .308 bullet may be travelling faster then a heavier one but at say 600 yards the lighter bullet sheds more velocity so that the heavier bullet is travelling faster. BTW these are just numbers I pulled up for example not to be taken as true numbers.

Ballistics are a bit more complicated than what can be throughly discussed on a forum.

[WRMETTLER]

This is an interesting subject.

Bryan Litz is engaged in a thread about this subject here:

http://www.usrifleteams.com/lrforum/...ic=13415&st=75

It seems that there are many different issues relating to the stability of a bullet as it passes through the transonic zone and merely by passing through the transonic zone a bullet does not necessarily become either unstable or inaccurate.

[Brush Okie]

Originally Posted by WRMETTLER

This is an interesting subject.

Bryan Litz is engaged in a thread about this subject here:

http://www.usrifleteams.com/lrforum/...ic=13415&st=75

It seems that there are many different issues relating to the stability of a bullet as it passes through the transonic zone and merely by passing through the transonic zone a bullet does not necessarily become either unstable or inaccurate.

Yor link goes to a log in. Intresting I would like to hear more about it.