How Far ?

[sunbuilder]

In general,

Do you think it's a fair statement to say;

Maximum potential effective distance for a bullet is limited to the point it becomes sonic?

Assuming all other conditions are perfect.

Another way to ask would be;

Does the "transonic buffing effect" create an accuracy "wall"?

I think it does.

Just wondered what you thought. Nothing specific in mind.

Scott :crazy:

 

[savet06]

Must be something to it or all the long range guys wouldn't always be hunting for the load that keeps them supersonic at 1000yds.
That said there are many "effective" and accurate subsonic rounds out there that offer a lot to hunters. Just maybe not the ultimate in accuracy that many benchresters try to achieve.
My novice $.02
Mike

 

[alf]

Gryroscopic stability plays an important role when going subsonic.
Several are shooting BIB 187 FB's at 1000yds with great success.
As with most things in the shooting sports, not everything is written in stone.

Al

 

[britz]

For the most part, yes. Passing through the sonic barrier can be very hard on accuracy. With that said, some of the very good high BC bullets will be less affected by this. So, it is possible for some very high quality bullets to stay quite accurate after passing through the barrier. At least that is the infoe that I have.

 

[CatShooter]

In general,

Do you think it's a fair statement to say;

Maximum potential effective distance for a bullet is limited to the point it becomes sonic?

Assuming all other conditions are perfect.

Another way to ask would be;

Does the "transonic buffing effect" create an accuracy "wall"?

I think it does.

Just wondered what you thought. Nothing specific in mind.

Scott :crazy:

There is no "buffeting effect".

Above the speed of sound, 90% of the energy is lost in the nose shock wave, and as the bullet slows down, this wave gets weaker and weaker... just above the speed of sound, the nose wave is minuscule... almost non-existant.

As the bullet goes below the speed of sound, the nose wave just simply disappears.

There is no shock or buffeting,those ideas come from too many old WW2 movies).

The transition from above the speed of sound to below the speed of sound is smooth and seamless.

The above is not "my opinion"... it comes from thousands of shadow graphs fired at Columbia University when I was a research consultant... we were studying the flight path of really small projectiles.

There are some cases where bullets will hit sideways at long range, and often it is blamed on "going through the sonic wall"... but there is no such wall, as witnessed by the fact that many shooters are shooting at VERY LONG RANGE, withOUT these problems.

In Scotland, there is a group of crazies that are shooting at 2,000 and 2,200 meters, with 308s, 303 Brits, and 30-06s, and hitting very well,nose first!!)

The instances of bullets hitting sideways can be attributed to not enough twist,it being marginal to start with), or some irregularity in the "system".

There is a fellow out in Arizona,or New Mexico) that was written up in Precision Shooting some years back that was shooting at steel plates at 3,000 yds,and hitting them) with a 308 AI.

He was using a special scope mount that was tilted down 7.5 degrees.

Don't let the "sonic wall" get you down...


.

 

[boogershooter]

Catshooter,What twist do you like in .308? For 175 SMK's At long range, say 600 to 1000 yds .And will it still shoot good groups at 100 .
Thank You Sir!

 

[rstreich]

Catshooter's right about there not be a buffeting effect. The instability is caused as the center of pressure moves towards the front of the bullet as it slows to transonic speeds. For some bullets, it's like a wall--the .30 168 gr. MatchKing being one of the more notorious. I don't think anyone has come up with anything to predict which bullets will destabilize and which won't. Personally, I suspect the old 55 gr. 5.56,M193?) bullets would fall into this category also. Lots of keyholes, frequently in the frames, of the targets I was pulling.

However, twist rate doesn't really have anything to do with it. If a bullet has enough spin,gyroscopic stability) as it leaves the muzzle, it has enough at any point downrange.

Catshooter, what kind of projectiles were you taking pictures of? It sounds like a fun piece of work. But I suppose after thousands, it might have gotten a little tiresome. I went and dug up a post by Brian Litz where he reported some Air Force modeled, not empirical, data predicting that for a Berger 180 gr. VLD, the actual loss due to wave drag was down to 65%. Here's a link to the post.

 

[284driver]

There is no shock or buffeting,those ideas come from too many old WW2 movies).

The transition from above the speed of sound to below the speed of sound is smooth and seamless

That's not what i learned from Chuck Yeager in the movie "The Right Stuff"
lol

 

[mikecr]

Looks to me that drag peaks right at Mach1 and reduces both sides of it. It hits hard both increasing and decreasing into it.
This is based on any drag curve I can find as well as shadow graphs. Bullet stability is also directly tied to mach1, as it dips right at it.

This is the first time I've ever heard an implication that mach1 is insignificant, and I for one do not believe it at all.

 

[284driver]

At sea level, 3000fps is mach 2.68
mach 1 is 1116fps, or 761mph. So, as long as the bullet leaves the barrel above mach 1 and doesn't slow below 1116 fps, the buffeting is probably irrelevant. wonder how slow a 308 gets down to at 1000 yards?

 

[Bryan Litz Ballistics]

Mike,
Don't be mislead. Those drag curves you refer to are depictions of the dimensionless drag coefficient, not the drag force. The drag force is proportional to velocity squared, so drag at higher speeds is always greater than drag at lower speeds. The shape of the drag curve causes the drag force to be not exactly proportional to velocity squared. In other words, the drag rises more sharply near Mach 1, then goes back to increasing,almost) with velocity squared for supersonic speeds. The reason it's 'almost' increasing with V^2 is because the drag coefficient is now decreasing, as you pointed out from the drag curves. Bottom line is: drag force is always greater for higher flight speeds.

All,
The term 'buffeting' is a little too ambiguous to argue whether or not it happens to bullets at transonic speeds. Certainly, the greatest transients the bullet will experience during it's flight occur at transonic speed. Large swings in drag, dynamic stability, etc. happen, and sometimes it's enough to make the bullet tumble. If the bullet does tumble as a result of transonic flight, it's not for lack of gyroscopic stability,AKA static stability). Tumbling at transonic speed is a consequence of inadequate dynamic stability, which is very different from static stability. One common myth that's stemmed from this misunderstanding is that increasing spin will help the bullet fly thru transonic speeds without tumbling. This is not true since increasing spin only increases static stability but not dynamic stability, and it's dynamic stability that's the problem. The bullets that do have dynamic stability problems,the .30 cal 168 SMK being the classic example) have the instability at all speeds, even when comfortably above sonic speed. Unlike static stability which is required for point forward flight, dynamic stability is preferred, but not required. What I mean is, a bullet can fly point forward with dynamic instability, but not with static instability. When a bullet flies with dynamic instability, it just means that the 'conning' motion isn't completely damped. In laymans terms, the bullet never 'goes to sleep'. In fact, the bullet's conning motion will continue to grow as it flies,the bullet's always 'waking up'). This causes more drag on the bullet than what's predicted by traditional ballistics programs, which assume no conning motion. When bullets like the 168 SMK get down near the transonic flight speed, the dynamic instability grows, and causes the conning angle to increase more rapidly. The two important results are:
A) the bullet slows to transonic speed earlier than expected due to the conning motion at high speeds
B) When the bullet reaches transonic speeds,earlier than expected), the conning motion increases to a catastrophic level.
So bullets flying with dynamic instability don't really hit a 'wall', but more of a 'ramp'.
As rstreich stated, it's hard to tell which bullets will have a dynamic instability. The aerodynamic coefficients which govern it are very hard to predict.
To address the original question of 'how far'? I can only offer that if a bullet does make it thru the transonic flight regime, it will continue to fly subsonically... indefinitely until it hits something. ,an exception is if the bullet is fired at such a high elevation angle, like 80 degrees, that it fails to 'trace', and falls back down base first) For certain, the bullet will be most sensitive to wind and other atmospheric influences during it's very short time spent at transonic speed. This is a reason for the bullets being less accurate after flying thru transonic.
If the bullet doesn't make it thru the transonic regime, obviously that's the limit. Range can be extended only by increasing muzzle velocity and getting the bullet farther downrange before the bullet slows to transonic.
Take care,
-Bryan

 

[BigJim]

Bryan - that is a great response but I had trouble getting through all of it,it was long). What is the "transonic" stuff. Super sonic and sub sonic I get but are you talking about transitioning back to sub sonic?

Well that doesn't matter. I would guess that the bullet goes super sonic about 1 inch up the barrel and does not slow to sub sonic until both air resistance and gravity have had sufficient effect upon the metal in the bullet. That brings up the question that since gravity has more effect upon the bullet than speed. Is the rate of drop greater over a field of Farris metal that clay dirt???? Does that mean we have to take soil samples before shooting any field?

Boy and all I wanted to do was have fun shooting, now I have to go back to school and take another physics course.

Big Jim

 

[harvey13118]

Big Jim only if you're shooting steel core bullets.

 

[jthyttin]

Bryan - that is a great response but I had trouble getting through all of it,it was long). What is the "transonic" stuff. Super sonic and sub sonic I get but are you talking about transitioning back to sub sonic?

Transsonic is the "near-sonic" zone. If you want to play safe, it's maybe from 0.8 Mach to 1.2 Mach. In other words, about 200fps on either side of the speed of sound.

As Bryan explained, this is the "ramp" instead of "wall" at the exact speed of sound. I don't know if the 200fps is right number for bullet stability calculations, I use it when loading subsonic with silencer,I keep loads at 0.8 Mach,900fps) so flight noise is kept at minimum).

 

[BigJim]

Harvey I may be wrong,it won't be the first time) but if I remember the periodic table correctly lead is heavier that iron more electrons and neutrons and all that stuff. What I was trying to point out is that gravity will limit the travel of any object in relation to it's weight in a greater relationship than air friction. Now if you were dragging the bullet along the ground that might have more of an effect on how far it travels. I have a friend that thinks all his loads should be at max bullet weight and max powder loads. Not only does he want whatever he shoots to drop dead right there on the spot but wants it gutted at the same time. He fails to understand that a lighter weight bullet traveling at a much higher speed will impart more foot pounds of energy and do more damage,hydrostatic shock) than a heavy 230gr head that can not obtain the same speed no matter how much powder you put behind it unless you blowup the gun or use a tank for your rifle.

We have not even covered air density and the effect of humidity on the travel of the bullet or the fact that it would be heavier at the north pole than at the equator. Yes the electromagnetic field of this planet does have an effect on all things iron copper or lead. Some more than others.

As for me I will try to stay within a range that I have tested and know I can hit the target accurately at.

I like the idea of a ramp, I hate walking up the stairs,LOL)

 

[Bryan Litz Ballistics]

The force, and resulting acceleration,de-cceleration) attributed to aerodynamic drag is far more than the force and acceleration of gravity.

Consider this example:

.243 95 grain VLD fired at 3000 fps in standard sea level conditions will slow to just over 2800 fps in the first 100 yards. Time of flight is 0.1032 seconds. That's an acceleration of -200/.1032 = -1884 ft/s^2.

Compared to the acceleration of gravity: -32.2 ft/s^2, the aerodynamic drag acting to slow the bullet down is 59 times greater!,59 G's).

Obviously, gravity acts to accelerate the bullet down, towards the ground, and the aerodynamic drag acts to slow the bullets forward speed. The two combined forces and accelerations determine how far a projectile can be fired.

Any electromagnetic effects that arise from the bullet,a conductor) moving thru the earths magnetic field are insignificant compared to aerodynamic drag and gravity.

 

[BigJim]

OK here is the test two bullets fired exactly at the same time from exactly the same make of rifle with the same length of barrel with the same primers and powders at the same load of powder but one bullet weighing 55 grains and the other weighing 80 grains both full metal jackets.

Which one will travel farther and why?

Yes this is a kinetic energy problem so sharpen you pencils you will be graded on your answer.

Thanks
Big Jim

 

[Bryan Litz Ballistics]

It depends on the angle of fire.

Obviously, the lighter bullet will come out faster than the heavier bullet with the same powder charge.

For very shallow angles of fire, the lighter, faster bullet will be 'flatter', meaning it drops less than the heavier slower round. So if both are zero'd at 200 yards, the 80 grain bullet would hit the deck before the 55 grain bullet after 200 yards.

However, due to the higher BC of the 80 grain bullet, it will retain velocity,and KE) better than the lighter bullet. At some point downrange, the heavier bullet will have a greater velocity than the lighter bullet. At some point farther downrange, the heavy bullet will have a lower time of flight than the lighter bullet that started out faster.

If both rounds are zero'd far enough away, like 600 yards, the 80 grain bullet will be dropping at a slower rate,drop per yard traveled) so it will impact the ground farther downrange than the 55 grain bullet, if both are zeroed at 600 yards.

Of course, in the 'max range' scenario, where you're firing at the optimal angle for longest range, the heavier bullet that started out slower will indeed travel farther because it maintains a higher average velocity throughout the flight. Over long range, this makes up for the fact that is started out a little slower.

Of course, in the absence of air resistance, the answer is much different, but who cares about shooting on the moon?!




OK, I care!
In the absence of air resistance, many things change. For one things, wind flags don't work worth a dam!
With no air resistance, the rounds fall to the ground with the same KE as they were fired with,and the same velocity). The optimal angle of fire is 45 degrees for both. Gravity accelerates both downward at the same rate. The only difference is the lighter bullet will start out faster, have a greater apogee, a greater tof, and a greater range.
Air resistance makes BC relevant, and reverses the answer in the max range scenario.

So, how'd I do?

-Bryan

PS I suspect part of this 'test' was to acknowledge that both bullets would exit the muzzle with equal kinetic energy,because both are converting the same amount of stored, potential energy in the given powder charge) However, due to the complex internal ballistic interaction between heat, pressure, burn rate, etc, I think the heavier bullet gets quite a bit more KE than a lighter bullet from an equal powder charge. It certainly gets more momentum as indicated by greater recoil!
Momentum vs KE, now there's an interesting test...

 

[BigJim]

Bryan - You get an A+ Thats why your loading tables will recommend less powder for the 80gr head than the amount of powder for the 55 grain head. Excelent answer.


Big Jim

 

[mysticplayer]

Bryan, thanks for post #11. That answers the question that has been bugging me for years. Increasing twist doesn't do spit. If a bullet tumbles, it will tumble.

also, cleared up my thoughts on the 'wall' and what that meant. Great stuff.

Now I can add some real world data as I have been playing with extreme shooting lately.

Out of a 223, 7 twist Pac Nor, the 75gr Amax,2950fps) and 80gr Amax,2850fps) WILL make it to a mile and do so accurately. By accurate, I mean able to hit a MOA or smaller object IF you can figure out the winds. A very small change in wind speed or direction and you are WAY off course.

3 of us were able to put multiple hits on a 12"X 12" rock once we figured what the winds were doing.

The Berger 80gr VLD will also make the trip but I had very few bullets so not well tested. I did find that vertical stringing on a few occasions was enormous. Where the amax might get bounced a few feet, the Bergers were dropping many yds short.

The 300gr 338 MK WILL get out to 2400yds when launched at 3100fps/10 twist. Very accurate even in the winds. Certainly a driveable bullet.

The 750gr AMax out of a BMG makes this trip no problem either. Think 2700fps thereabouts.

The 6.5 139gr Lapua Scenar out of my 6.5 Mystic,2900fps, 8 twist) goes 2400yds but like the 223, it gets bounced around at that distance. Dropping to 2200yds made for a very driveable distance. Could simply have been more turbulence at the longer distances???? Ran out of up so couldn't go to 2700yds.

The one surprise was the 175gr MK out of a 308. The last time we tried this, at 1300ish yds - no problem. A little past 1400yds, spray and pray. Ok, same concerns as the 168gr MK but it just shows up further out due to higher BC, yada, yada.

On the weekend, we had several take their 308's,different rifles) well past 1400yds with one getting out to 1800yds ACCURATELY. Twist rates should be similar 1" extra spin at most. Velocities are all in the same ballpark so this bullet is a mystery.

I was very pleased to see so many bullets make the trip. To dope the conditions that far is so demanding but fun when you get it right. We are shooting at boulders that range from under MOA to 3 MOA so this is not indicative of 'group' accuracy. Think static varmints.

But these bullets can be driven with good effect. Sorry, no 6mm, 7mm's were shot this weekend.

Jerry