[JimL]

I can't even find the article any more, but it had a statement that sounded a bit over the top. I'd like an expert opinion to settle the matter.

The statement was that many super-sonic rounds have poor accuracy, because of a double super-sonic effect. That the bullet is shaken up when it breaks the sound barrier, then is shaken up again when is slows down below the sound barrier, throwing it off track under certain conditions or bullet configurations.

Help! :???: :???: :???:

JimL

 

[NativeTexan]

Tell that to my sub 1 MOA (that's one inch at 100 yards) rifles, which include a 3300 fps 150 grain 7 mag load. That's over mach 3. My Blackhawk routinely puts 'em into less than 1" at 25 yards with iron sights firing a 180 grain bullet at 1401 fps, if you want handgun accuracy. I can put that one into 6" at 100 yards, no doubt would do better with a scope.

Simply bull caca. Proper rifling rate for the bullet is much more important. Velocity has NOTHING to do with accuracy within the effective range of the given load.

 

[JimL]

Simply bull caca.

May I quote you on that? ;D

JimL

PS

Is caca anything like cactus?

 

[KD5NRH]

Tell that to my sub 1 MOA (that's one inch at 100 yards) rifles, which include a 3300 fps 150 grain 7 mag load.

My guess would be that, if the bullet is properly made, (symmetrical in both shape and weight distribution) and the twist rate is right, the sonic transitions should be pretty much irrelevant. They would make a lot more difference if the bullet was either lopsided in shape or weight distribution, (core not centered in jacket, etc.) though probably not nearly as much of a problem as it would have already suffered from the spin.

 

[8times.357]

I have read similar things JimL, but the bullet is still in the barrel when it goes supersonic, so the issue occurs when it goes subsonic.

Aircraft have to deal with the acceleration related instabilities when they go supersonic. The rocket powered X1 was modeled after the .50 BMG because that was a shape that was known to be stable at supersonic velocities - but no one knew if it could survive accelerating through the "sound barrier".

http://en.wikipedia.org/wiki/External_ballistics

Excerpt:

The transonic problem
When the velocity of a rifle bullet fired at supersonic muzzle velocity approaches the speed of sound it enters the transonic region. In the transonic region, an important thing that happens to most bullets, is that the centre of pressure (CP) shifts forward as the bullet decelerates. That CP shift affects the (dynamic) stability of the bullet. If the bullet is not well stabilized, it can not remain pointing exactly forward through the transonic region (the bullets starts to exhibit an unwanted coneing motion that, if not dampened out, can eventually end in uncontrollable tumbling along the length axis). However, even if the bullet has sufficient stability (static and dynamic) to be able to fly through the transonic region and stays pointing exactly forward, it is still affected. The erratic and sudden CP shift and (temporary) decrease of dynamic stability can cause significant dispersion (and hence significant accuracy decay), even if the bullet's flight becomes well behaved again when it enters the subsonic region. This makes accurately predicting the ballistic behaviour of bullets in the transonic region very hard. Because of this marksmen normally restrict themselves to engaging targets within the supersonic range of the bullet used.

 

[NativeTexan]

IF a bullet is cast unbalanced or with flaws, it won't take supersonic speeds to make it inaccurate.

 

[8times.357]

Just checking the Federal ballistics tables - the distance most rifle cartridges' bullets go subsonic seems to be well past 500 yds. So it seems this won't affect the vast majority of shooters at all.

ETA:

http://www.exteriorballistics.com/ebexplained/5th/24.cfm

Here's what it does affect;

"But at the present time, accurate long-range trajectories simply cannot be calculated for bullets that travel at lower transonic and subsonic velocities. This affects the ballistics of rifle cartridges such as the 30-30 Winchester, 35 Remington, 444 Marlin, 45-70, and the “Whisper” class of cartridges, as well as all handgun cartridges chambered in rifles.
"

 

[NativeTexan]

I still call BS. I have a .22 LR Remington M512 X that, on a windless day, will put 10 rounds into a 1.5" circle at 100 yards all day long with FEDERAL LIGHTENING bulk pack that has sub 1300 fps muzzle velocity. Now, I haven't run the numbers on it, but I'm quite sure it's subsonic somewhere between 50 and 75 yards.

Snipers routinely make hits out to 800 yards with the .308 MV somewhere around 2700 fps. I haven't calculated an 800 yard velocity, but that's pretty impressive. The longest shot taken was somewhere around a mile by a Canadian sniper using a Barrett in 50 BMG in Afganistan. The bullet leaves the barrel at 2800 fps, but does have a ballistic coefficent of around 1.00. However, a range of 1700 yards, I'd have to work that one out with my old program I wrote in Basic cause I doubt any normal exterior ballistics program will calculate that far. LOL. I could do it with my old program, but I've not fired that Tandy computer up in 15 years. All I'd have to do is change a few numbers in the "do loops" (okay, a fortran term) in the program to calculate it further out, but it's too much a pain to go through all that just for this thread.

Anyway, I've never seen a problem of such a nature. I looked through my trajectory tables to see if I'd run one for my .357 Rossi carbine. Never did, guess because it's a 100 yard gun and why worry about a drop table. It may be supersonic at 100, though, since it starts out at 1900 fps. However, My 180 grain load in my Ruger blackhawk starts out at 1400 fps and is probably sub sonic at 100 yards, I'd guess around 800-900 fps. That gun with that load shoots 4" groups at 100 and 1" groups at 25 when I can get my old eyes to work.

 

[NativeTexan]

Here's what it does affect;

"But at the present time, accurate long-range trajectories simply cannot be calculated for bullets that travel at lower transonic and subsonic velocities. This affects the ballistics of rifle cartridges such as the 30-30 Winchester, 35 Remington, 444 Marlin, 45-70, and the “Whisper” class of cartridges, as well as all handgun cartridges chambered in rifles.

Well, that's probably because of varying ballistic coefficients for subsonic rounds which doesn't affect accuracy so much as the accuracy of ballistics programs to calculate velocity loss. I know in the case of MY program, the mathematics go haywire somewhere around 800 fps and you can tell that in the program because all of a sudden, the model says the bullet is accelerating. LOL! But, it's quite accurate at over 1200 fps and indicates to you when you should ignore the numbers. I got the derived algebraic formulas from an article in Rifle Magazine written by a PhD mathematician with New Mexico State University and he warned of this in his article and gave a mathematical explanation that I've since forgotten, but IIRC it had something to do with the BC changing sub sonic.

Let me explain that a little more, but BC is NOT fixed for a given bullet, it has variables like drag coefficient in its makeup. Drag coefficient, of course, is radically different for a supersonic projectile than a sub sonic one so this changes BC. But, for the same bullet at the same velocity, all bullets should have the same or real close BC, so they will be accurate even if you would have difficulty calculating velocity loss at range (and therefore a drop table) because the BC suddenly changed so you won't be able to predict accurately the drop of the bullet. It will just have to be done by shooting at range, actual experimentation.

 

[8times.357]

NativeTexan,

From what I've read, I think that the authors are saying some bullets with some spin rates will become more unstable than others as they slow to subsonic. I don't think you would notice much at 100 yds even with a .22 - but I don't know, of course they wouldn't be tumbling or anything drastic like that. I probably don't have 1/10th the experience you do at 100 yd shooting. What I wonder is if those 1.5" groups become 7", 10" or 16" at 200 yds due to this transonic thing. You could say that the round is accurate within it's effective range, but is it's effective range, in part, determined by how soon the bullet goes subsonic?

I agree that the exterior ballistics info from the Sierra manual doesn't apply, it is as you said a problem with calculating the theoretical...

I find your ballistics experience very interesting and admirable.

ETA: I think I saw a typo, 1 mile is 1760 yds.

 

[NativeTexan]

I can't remember the actual yards that canadian sniper fired to kill that guy, but it was impressive, something around 1700 yards or near a mile IIRC, but not exactly 1760 yards. Not only that, but the 50 had enough snuf to penetrate light armor and killed the guy behind it! WOW, that 50 is impressive! LOL! I read about that shot in a magazine and then they were talking about it on a show on the military channel the other day called "Weaponry" or something like that, all about modern weapons and development. The guy that narrates it is an ex-seal sniper.

I doubt that many calibers effective range would be determined by where it goes sub sonic because that point it's falling like a rock. My 22, would probably be pretty impressive at 200, but I don't think I have enough adjustment in the scope I have on it, ROFL!!!! We have a 200 yard range and I fire on it from time to time even with my Contender pistol, but I've not tried to shoot a rimfire down there, just seems like an exercise in futility. Not only is the trajectory a rainbow, but wind drift is aweful on a .22 if there's any wind at all. The times I've fired at 300 was from the gate down to the 200 yard target boards and no one else was at the range. Now days, don't get to do that much cause the club has a lot of members now and the range is rarely vacant, but that's a good thing for the club, I guess.

So, what I use my ballistics for when I develop a load is mainly to assure me that it has enough energy to X yards to do the job and to know where to set it at 100 for maximum point blank range. I generally use a 3" maximum point blank range for deer and hogs on my rifles. Generally, there ain't a lot of difference from caliber to caliber in the better rifle calibers, though, and unless I go out west, the exercise is moot cause I can't see past 200 yards in the brush from my deer stands on my place, LOL! However, having a good knowledge of your rifle, especially spot and stalking mulies out in New Mexico's arid mountains, is a good thing. My personal limit for hunting is 400 yards and my programs do a decent job of prediction to that range and more. I know there are those who brag about 600 yard shots on the various boards and good on 'em, but I don't have the facilities to do that kind of shooting and the variables, like wind drift and up or down hill incline, are too much for me to be trying that long a shot even if I lase the range and know the bullet drop. So, my limits are self imposed. There's more to consider than just drop or velocity induced accuracy losses, which on a .308 or 7mm Rem Mag or even my .257 Roberts is going to be well above sonic as you pointed out earlier. Even if in some way, you loose a little bit of accuracy from SOME rounds with SOME twist rates, okay, I can see that, it won't affect me and my shooting, so it's moot for all practical purposes, at least for me and what I do with a firearm.

 

[NativeTexan]

Hmm, I found and corrected that typo. 7000 yards? ROFL!

 

[8times.357]

Hmm, I found and corrected that typo. 7000 yards? ROFL!

I think you meant feet! The distance in meters was 2,430 (close to 8000 feet), that was the 2nd Canadian sniper to break Carlos' record and set the new one. That's also about the altitude they were operating at.

FWIW, I just read a "White Paper" for the .408 Cheytac rifle that claims the .50 ball is sonic to 1700 yds, and when it goes transonic it undergoes "extensive vibrations". It also claims the .408 is supersonic at 2400.

 

[JimL]

I could do it with my old program, but I've not fired that Tandy computer up in 15 years.

Oh the good old days. I first learned BASIC on a Tandy CoCo with a huge 16K of memory.

JimL

 

[JimL]

therefore a drop table) because the BC suddenly changed so you won't be able to predict accurately the drop of the bullet. It will just have to be done by shooting at range, actual experimentation.

Either that or one really, really, really h___acious algorithm.

JimL

 

[JimL]

Anyway, I've never seen a problem of such a nature.

Web page experts, right? Practicality isn't always high on their agendas.

I was just reading one by a rental "ballistics expert." He said there is more to "accidental firing" issues then just pounds of trigger pull. Fine. Length of pull is a factor. But he mixed so much rhetorical nonsense in with the facts it just wasn't real or useful.

JimL