Oft times we read articles whereby the author of whatever talks about a particular bullet or cartridge not being accurate because it can't remain supersonic throughout the distance to the target as it goes into the transonic stage...the bullet gets 'squirrelly' and accuracy suffers! One example of this is in years past when working the pits we could always tell who the Service Rifle shooters were when shooting 1000 yards because oft times the 168 gr. Sierra bullet being used would keyhole into the target paper! That bullet was NEVER designed as a long range bullet in the first place, however it set world records over many years in 300 meter matches! It had a 13 degree boat-tail and any bullet with that design has the same drag function as a flat-based bullet.

Now...here's some food for thought! The below photo is of a metal Creedmoor Target I had made a few years ago when I was heavy into shooting Sharps rifles using paper patched all lead bullets that I cast. There is a smaller plate inside the larger. Small plate is 20" diameter...larger bull is 44" diameter...same size as the Palma target. Ten ring is the 20" plate. I had this target made because when shooting from 1000 yards the bullet impacts stood out like a five carat diamond in a Billy goats ass in my spotting scope. I was testing a new load in my 50/90 Sharps using a 720 gr. paper patch bullet ahead of 116 grs. KIK 2F blackpowder using Russian primers. I wanted to see how the load held up for possibly giving a low vertical dispersion. Muzzle velocity of this load was around 1380 fps so it shouldn't take a rocket scientist to figure that this bullet was already below super-sonic at around 250 yards...or less! After a first round hit on the ten ring plate I made no adjustment for windage correction as the conditions were good with only slight wind and since I was testing for vertical....not a problem! Had I made a correction probably all ten rounds would have been within the ten ring plate. A measurement showed a 7.5" total vertical for all ten rounds!

So....in the final analysis...the question is why was the accuracy this good using a 125 year old bullet design using an out-dated propellent, moving at this below supersonic speed??? Another question is.....is all the talk about 'going into the transonic stage causing inaccuracy' just so much BS??

1000 yards 50/90 PP by .com/photos/61286670@N08/]Sharps Man, on [bleep]

I don't have near as much experience as you do, but I'm going to say it depends. The 175 SMK seems to transition through that velocity range pretty well. We shot quite a bit at extended ranges with M24's and 118LR before I retired.

On the other hand I was shooting at ground squirrels one afternoon with 6.5 139 gr Lapua Scenars and after barely missing one a couple of time at about 1350 I saw one a ways out further.

Long story made short my shots hit all over the place. I went back to where the closer one had been sitting on a rock and was able to hit the rock repeatedly.

Rifle is a Surgeon Action with a Krieger 1 and 8 twist Heavy Varmint Taper. I've killed a bunch of prairie dogs between 800 and 1150 yards with that rifle.

OUTSTANDING!!

Not Centerfire, but I'm almost positive I remember reading that the reason 22LR match ammo is subsonic is because the transition through the sound barrier made the high velocity stuff slightly less accurate. I can't remember when or where I read that. Probably some gun rag in the early 90's.

I don't have an answer to your question, but I have more questions for you;

We know about the 308, 168 Sierra 1000 yard trans sonic situation because of the M14 being used in Long Range Rifle competition. There was a convergence of different factors that made the transition observable. A) a rifle/cartridge/bullet combination that had a bullet going subsonic over B) pits with human observers to capture the phenomenon. How would us mere mortals know when a bullet was going subsonic without target pullers beneath the subsonic bullet or the resources of BRL Aberdeen to track these bullets going downrange? Could it be that other bullets are having similar instability issues, but it is going unnoticed because it is so far downrange beyond the benefit of a target with pits? Could dodgefan's 6.5mm anecdote be one such example?

With that said, I have heard that the 30 cal 173 M1 design bullets and it's offspring 175 Match King make the transition with stability as well as Berger's juggies. I've also heard that BPCR rounds do it without problem (those projectiles probably have a tremendous Stability Factor by virtue of their lack of zoot form factors). BTW, I've been in the pits with 405gr 45-70 bullets being fired at the 600 yard line. The steep downhill trajectory had us hugging the pit wall as they rained down on the pit roof. I don't care to do that again.

I quess one of the folks I`d like to talk to about the accuracy issue going from SS to sub-sonic would be Mark, from MarkandSam after work here on u-tube. He talks a lot about bullet design and it`s efficency at ELR. tho does not go into exact detail, but has found bullet designs that work extreamly well.
Brian Luts should also be a great source.
I`ve also thought of the problems Yeager and the Bell engineers faced in breaking the sound barrier,..going SS right, as simular The buffiting Yeager experienced in the plane...could suggest a bullet may do the same...at that point in it`s flight...causing inaccuracy beyond? They fixed it by a slight change in design.
Interesting topic tho...maybe someone with answers will chim in.

Wonder if there is a wind tunnel for testing bullet design?

I found these article interesting;

http://bulletin.accurateshooter.com...transonic-bullet-stability-and-accuracy/
https://precisionrifleblog.com/2018/09/17/extreme-long-range-tips-ballistics-time-of-flight/

https://www.asme.org/wwwasmeorg/med...n-Range-Aberdeen-Proving-Ground-1943.pdf

ChrisF and Sharpsman thanks for those articles they were all well worth reading IMO.

Yea....found the same ones..

Nice find! I was a member of ASME around that time! (Even got the t-shirt) ...and I don’t remember that newsletter.
FWIW, Bob McCoy did his work on documenting the flight characteristics of the 168 SMK at BRL. His book “Modern Exterior Ballistics” contained some good 168 specific research complete with spark shadow graphs...and my recollection was that he dissected the 168 transonic instability in detail there.

I was 'gifted' with the situation to have had several conversations with Bob McCoy over a ten year period. The first occasion was when I talked with him about what profile/design I should have my bullet making dies made? Bob advised that I should have them made with a rebated boat-tail and when I asked him why?? that design he told me that everything he had fired through the spark graph range with a rebated boat-tail had shown a minimum of a 5% increase in performance over the standard boat-tail configuration! That doesn't sound like much but in the case of having to make a 'shoot off'....a 5% increase in X count wins the pot!! I had Bob Simonson up in Michigan make my dies and I wore myself out over a ten year period making bullets of a specific design for shooting in the M14 as no manufacturer at that time was making a good match bullet for Service Rife shooters competing in NRA High-power events. Most shooters in the Service Rifle Class were tied to the Sierra 168 gr. HPBT which oft times, due to lack of adequate BC and muzzle velocity at 1000 yards would 'key-hole' into the target paper. The Sierra 168 bullet has a 13 degree tapered BT and Bob advised that any bullet with that degree of boat-tail had the same drag function as a flat-based bullet.

We lost a good guy when Bob was called home!!

Several years ago I built a rifle to see how far away I could shoot a Varmint and how far away I could shoot a target, I won't go into all the details but the bullet was a .338 Sierra 300gr Match King. It was very accurate out to 2144 yards on a rock chuck (my longest kill ever) but this bullet went transonic at 2300 yards...........at 2400 yards all accuracy was lost and would not hit a target of any size except the side of a mountain.

I’d be willing to wager that a faster twist would have transitioned the change from Super sonic to subsonic.

That could possibly be a valid point, it could also be possible that going to a faster twist could negatively effect accuracy. At this point it's not worth the price of a new barrel to find out. but interesting to ponder

Sharpsman, I've seen you recount this story several times on various sites. Can you help me understand this statement. What metric was McCoy referring to in that 5% increase in performance?
Do you have any samples of your 176 Delta's that you can share a photo of? I'm curious what they look like.

On a different note, I am pretty sure that your 176's did not drive Sierra to produce their 175's. It was actually PWS wanting an analog to the 173 FMJ for what ultimately became M118LR.

Brian Lietz shoots a 9 twist 308 at 1000yards with 210;grain bullets. Brian says that a faster twist gives a tighter spin to the bullet and a higher BC and at long range produces better accuracy.

That is interesting, Bryan Litz has also stated that the correct twist rate for a given bullet is optimal for accuracy and that unnecessarily high rpm can be detrimental.
This was in the pre-Berger bullet days...he might have changed his mind or the Brian Lietz you mention could be a different person entirely.

Bullets are better these days. Accuracy issues from over-stabilizing imbalanced bullets is not much of a problem anymore, unless you’re competing in SR BR, and 0.020” added to your group size can make or break you.

Bryan has given a more current statement of the effects of twist on accuracy, with experimental support, in his book “Modern Advancements in Long Range Shooting”, Vol 1.

Let's look at this idea closer. If you shoot a 300 gr bullet at 10/1 rifling ratio or at 9/1 ratio. It only gains 2 rpm over the length of a rifle. You really think that one extra rpm is gonna change much? Enlighten me on this? Once an rpm is reached to stabilize a bullet its done its job,yes no?

With a 30” barrel, a bullet fired in a 1/9” twist would get 3.3 revolutions but if fired in a 1/10” barrel, it would only get 3.0 revolutions while traveling down the barrel. So the bullet fired in a 1/9” barrel would be getting ~10% more RPM, not 2 RPM more The actual RPM would be dependent on its velocity.

Bullet RPM = MV X 720/Twist Rate (in inches)

https://www.accurateshooter.com/technical-articles/calculating-bullet-rpm-spin-rates-stability/

The formula matched up pretty close to what I got scribbling math on the back of an envelope.

A 338 cal 300 SMK at 2790 FPS has 200,880 rpms in a 10 twist barrel. The 9 twist barrel with the same velocity will have 223,200 rpm. This gives the 9 twist 22,320 more rpm’s.

Thats a whole lot of spinning. So is the rpm a constant? or does it slow as gravity and friction works on it while it flies? Does a long flat bullet rotate for ever at the same speed? If it is not a constant how can you apply your math to come up with that rpm?

The "5% increase in performance" Bob was speaking to was basically less drag and better stability throughout the entire flight path! I think my son has possibly a thousand or so of my 176 so I'll check and see!

Still can't follow. How does fps become rpm? Wouldn't you multiply by 60 to get rpm?I can't believe rotations in seconds would remain a constant for a long distance shot.

It doesn't remain constant, but the angular velocity (rpm) decays much slower than linear velocity (fps).

This is how I did the math before finding that formula.

Went to JBM ballistic found Time of flight over 100 yards for a bullet at 3000 fps which was .103 seconds.

100 yards = 3600 inches which means a bullet fired from a 1 in 10 twist will rotate 360 times during it's travel over a 100 yards.

1 (second) divided by .103 (TOF over 100 yards) = 9.708

360 times 9.708 = 3495 rotations per second

3495 times 60 = 209700 RPM

* I rounded the numbers off.

After thinking about it a bit more I realized why my numbers don't line up with the real smart guys.

(feet / second) * (turns / foot) * (60 seconds / minute) = rpm Just look at which units cancel out when the fractions are multiplied.

The only trick fill in is the turns per foot. An 8" twist will give 12/8 = 1.5 turns per foot.

Example for 3000 fps in a 10" twist: 3000 * 12/10 * 60 = 216,000 rpm

It might be easier to follow if we used simpler numbers;
If you are shooting a bullet out of a 12 twist barrel (1 turn in 12" which is 1 turn in 1 foot) at 3000 FEET per Second, the bullet at muzzle is making 1 revolution every 12 inches (1 foot). But that revolution is happening in 1/3000 of a second. In one second it will have made 3000 revolutions. In one minute it will have made 180000 revolutions (3000 revolutions x 60 seconds in a minute) and that is revolutions per minute (RPM).
As mathman has said, the spin slows down much more slowly than the forward motion.

I understand that you might be taking some creative license with that statement, but just in case...a 5% reduction in drag, would have to be translated into a reduction in wind drift which would then be SWAG'd into an improvement in score...
There was a guy named Larry Medler that ran a webpage where he played with such "what if" with ballistics and score. His site is down, but I'll see if I can find it in the wayback machine.

On a different note, Bob McCoy published his research on the flight characteristics of different match bullets. It's in the public domain, and it's a good read if you're interested in such things (from a historical perspective since the studied bullets have been eclipsed for long range shooting). Google "The Aerodynamic Characteristics of 7.62 Match Bullets".

Here's Medler's simulation;

Medler 600 yard simulation
Medler Palma simulation

Rotational velocity?

My head hurts

Should I throw a 2pi factor in there to get to radians per minute?

Nah, that’d just confuse the non-math/physics inclined folks even more. But you can’t blame a guy for taking advantage of an opportunity to poke mathman over a technicality- it doesn’t happen often!

You fellas went down the rabbit hole with this discussion, hope you enjoy the adventure!

There be a host of issues related to this discussion and frankly every "solution" has its own baggage. I'm going to throw a couple of things at ya to ponder, just for the fun of it.

Supersonic is what it is, but for purposes of this chat figure anything at or more than about Mach 1.3.
Transonic runs from about Mach .8-1.3.
Mach 1 at international standard atmospheric conditions is ~1116 fps.

The matter of bullet stability is commonly referenced to Stability Factor (Sf) which is a measure of gyroscopic stability acting against aerodynamic overturning forces. All conical bullets fly in a circumstance where the center of aerodynamic pressure is forward of the center of gravity. The displacement between the two is quite a bit different as a function of bullet form. RN bullets have little, needle darts have much more. The significance of this relates to the leverage that aerodynamic forces have on one form as compared to the other. Consider the drag curve below. Note how greatly enhanced drag is in the transonic realm. Note as well that the drag diminishes at higher velocity, but the problem is that your bullet begins to slow when it leaves the muzzle. When it hits the T-zone the forces at play get rather brutal and with spitzer forms this often results in upset.



My point is mostly that you can't have it both ways. The other side of the stability issue is that if one has a very high Sg it may induce degraded tractability, which in turn will cause upset.

Boil, boil, toil and trouble......

Will add this for your reading pleasure. Don't get lost in the gack.

http://www.nennstiel-ruprecht.de/bullfly/

dd I will take your word on it. it is above my pay grade

44mc, it really isn't all that complicated if you don't get lost in the details.

Short version? RB bullets launched in the T-S speed realm don't get all that ruffled by the extra drag/stability issue and definitely don't get upset when they get to where the buffalo roam. Downside is a fella has to know his drift and drops pretty well. Spitzers can be petulant little jokers, and they are somewhat prone to taking a break at long range. The OP's post illustrates the point I think regarding the RNFB. Modern match gospel illustrates the latter.

Modern day high tech shooters live with their self imposed limitations and cowboys DGAS, or something to that effect.

One of the more minor points about this that many overlook is that while bullet velocity is relevant to the transonic issue, bullet form is the bigger issue. Think of the air's movement as the bullet passes...it has to get around the bullet and to do that it accelerates. The bullet cross section and form define the nature of that acceleration and that would be why the T-Zone is a variable that encompasses a fairly wide range of velocity.

Excellent thread.