What effect does elevation have on twist rates. Does higher altitude require a faster twist to stabilize long bullets. Asking because just stared loading for a 25 06 with 1:10 twist Ruger #1. I've recall reading that the 115 grain Berger and 110 Nosler BT are a little unstable with 1:10 twist. We usually hunt above 5500 feet elevation.

Higher elevation usually requires less twist for the thinner air.

Don't know about the 110 Nosler BT. Nosler makes 100 and 115-grain .257 Ballistic Tips, so suspect you may be thinking of the 110-grain AccuBond. According to the JBM twist-rate program, either will be quite stable at 5500' above sea level, even in pretty cold temperatures--which is the other major factor in bullet stability.

It's pretty easy to calculate twist-rates these days, due to accurate computer programs. A lot of people use the Berger program, but it doesn't include any consideration for plastic-tipped bullets, which will stabilize in slightly slower twist-rates. Today's twist-rate programs are based on the Miller Formula, developed by the late Don Miller--but he later discovered that plastic-tipped bullets don't require as much twist as his basic formula predicts, because they're so light. The JBM formula includes an input for plastic tips.

I crunched a bunch of numbers from both the Berger and JBM formulas, and as a rule-of-thumb for the rifling twists used for most big game cartridges, 5000 feet in elevation equals about an inch in twist-rate. In other words, a bullet that will stabilize at sea level in a 1-9 in twist will stabilize in a 1-10 twist at 5000 feet.

I've never seen it quantified that way before. Pretty cool. Thanks, John.

Thanks!

I found it interesting as well--but then I'm obviously kind of curious! (In more ways than one...)

That's interesting. I had no clue that elevation had an effect on bullet stability.

As for stabilizing the 115 grain Ballistic Tips, they should stabilize in a 1:10 twist barrel up to 117 grains. I don't even know if there's a 117 Ballistic Tip. I just know that in my .257 AI with a 1:10 Twist that it stabilizes all bullets up to 117 and a few 120 grains. That's what the barrel maker said anyway. My .250 Savage has a 1:9 twist and it stabilizes all bullets up to 120 grains. I've never tried anything heavier. That's what Krieger told me it should do. The one 120 I've tried in it was a Speer and it seemed to stabilize it ok.
But for what I do I don't need a 120 in either rifle. The 115 grains do everything I need.

Filaman,

How are you defining "stabilize?

And no, Nosler does not make a 117 Ballistic Tip, but they do make a 115.

Thanks John. You're are right, I was thinking of the 115 BT.

Never a bad idea to spin em fast...

Mule Deer, my understanding of stabilize is the twist rate causes the bullet to spin at a certain rate. This spins the bullet fast enough where it will fly true like a football. If too long a bullet and too slow a twist the bullet will wobble and won't fly true.
However, I don't know how far the bullet will fly straight. If it is borderline stability, as it loses velocity at some point it will become unstable, and begin to wobble resulting in loss of accuracy from that point onward. That's my understanding of it anyway.

BTW, I normally use 115 grain Combined Technologies Ballistic Tips. They shoot very good in my two .25s.

Filaman,

You have stability backward, but many people do. Spinning bullets do not become less stable as they slow down.Instead they become more stable--at least at the ranges most people hunt big game.

This because there are two opposing forces on spinning bullets--the spin, which gyroscopically stabilizes the bullet, and air pressure on the front of the bullet, which destabilizes them. The rate of spin has to be sufficient to overcome the frontal air pressure (and yes, these are exactly the same forces at work on a thrown football).

The rate of spin produced by the rifling and muzzle velocity drops very slowly as the bullet passes through the air. The bullet's velocity, on the other hand, drops comparatively rapidly, which reduces the air pressure on the front of the bullet, making it more stable.

The main reason many shooters think a bullet destabilizes as it loses velocity is wind-drift--which increases about twice the rate as range. For instance, if a given bullet drifts 2 inches at 200 yards in a 5 mph wind, it will drift about 8 inches at 400 yards. This effect occurs even in very mild breezes, so mild many shooters don't even bother trying to compensate for wind-drift, instead aiming directly at the target. This results in larger groups at longer ranges, which many shooters believe are the result of bullets losing stability. But they're not.

There is an exception as bullet velocity drops below the speed of sound, about 1125 fps at lower elevations, which creates some turbulence. That's why .22 rimfire match ammo typically has a muzzle velocity slightly below 1100 fps: They leave the muzzle at less than the speed of sound, so don't drop through the "transonic zone," and long-range centerfire target shooters try to keep their bullets supersonic. But the velocity of most modern varmint and big game bullets does not drop anywhere near the speed of sound at typical hunting ranges, so become more stable during their entire flight.

Great explanation MD, thanks.

Thank you sir. That makes sense when you explain it. But you're right, there's a lot more than me that have that wrong. I need to study your explanation to get it stuck in my 72 year old mind. I hope you don't mind, I copied your explanation and put it in a file in my computer. I'm not a ballistician by any means but I'm very interested in ballistics. Just bare with me, I'm learning and I ain't dead yet dude !

We used to think that they did better as they slowed down but now we are learning, through the ELR shooting, that a bullet that is apparently stable (using doppler RADAR to monitor) will to to hell at certain ranges unless it has enough twist. A bullet that seems to fly great at 1000 yards will often yaw and wobble at 2000 yards. A lot of the ELR guys have good to very fast twist rates to combat this. 20x caliber is a good starting point with the copper bullets for true long range stability.

I have killed deer with rifles sighted in at long range in 25-06 and 257 Roberts Ackley rimmed, both with 115 gr Nos Bal Tips. Both with 10" barrels I threaded and chambered. No problems.

Yep, higher elevation means less drop too. Had that argument with someone before. But I promise you a 75gr Amax shot at sea level drops a hell of a lot more than the same bullet at 6000 feet.

Cold can really screw some stuff up, concerning twist.

I have a 260 AI that shot 130 Normas great at 5400' when i lived in Prescott, at 1300' they group 3-4". I guess they were on the ragged edge for 5400' .

I'll probably never order another barrel with less than 1:8 twist unless it's for a 458 or 9.3.

Clark,

Like almost all .25-caliber bullets made today, the 115 Ballistic Tip was designed to stabilize under just about any conditions in a 1-10 twist, even from a 1-10 .250 Savage.

That makes perfect sense, pressure is directly related to area which is a 'squared" function.(pi r^2)

Likewise cold air is more dense than warm air.

So here is the question is does elevation help the winners or the losers more because of the square?
Does the flatness of high BC bullet improve more or less than a low (dirty) BC bullet?

Why don't you check that out with one of the excellent computer ballistic programs available free on the Internet these days?

Of course, to do that, you need good ballistic-coefficient data, and one thing most average hunters don't realize is that BC not only varies with elevation/temperature/humidity etc., but with velocity and bullet shape. What may theoretically apply to a certain bullet with the standard G1 BC (basically a flat-based spitzer) will not apply to a G7 profile high-BC boattail.

Which is why I've been recommending Bryan Litz's excellent book, BALLISTIC PERFORMANCE OF RIFLE BULLETS, for several years. Not only does Bryan explain all of this excellently in terms most of us can understand, but he also lists the BCs of a bunch of commericial bullets from .17 caliber on up, at varying velocities and conditions. The BC's were not just derived by calculations but partly by actual shooting at his facility in Michigan.

I have used Bryan's BC's with a bunch of bullets when shooting out to 1000 yards at the local range, and in every instance they have been just about dead-nuts. You can order the book from www.appliedballisticsllc.com

So some remain beyond his reach.

Good point!

Thanks John.
I have read a few of his papers. Very good stuff. The Lilja stuff is good too.

Actually I think between this thread and the barrel length and velocity thread I just "got" internal external ballistics...
So hear me out Sir wordsmith, man of great experience, and see if I can put it in words. Spare not the rod.

We talk about velocity because velocity is easy to measure (at near distances).
But what we are really concerned with, in both internal and external ballistics, is positive and negative acceleration (a squared function). Not so easily measured externally until Doppler became available to shooters.

Internally, the bullet is accelerating until one of several things occurs. Which is why there is no linear relationship between velocity and length.
1) bullet exits the barrel
2) ~95% charge is consumed
3) pressure drops below that required to accelerate in the face of frictional losses.

Barrel exit can be, but is not always the inflection point between acceleration and deceleration (see number three above)

Deacceleration is affected by:
1)BC
2)Air pressure (another square function)
3)air density (related but not synonymous with the above)
4)stability
5)angle of attack?. ..
6) wind
?)

So since square functions are curves as opposed to linear relationships are they not the variables we should be most concerned with?

Thanks..

Quia unum exemplum

Apparently!

Pope say a what a?

the 130 normas have been shooting great out of my two 1-8.5 twist barrels.

My model 70 257 Roberts shots 110gr Accubonds and 115gr Partitions great. In fact the 115gr Partitions are the most accurate bullets in my rifle.

120gr Partitions are just ok the group opens up with those bullets, so I do not use them anymore.

The 120 Partition also stabilizes well in the standard 1-10 .25-caliber twist, because like the 110 AccuBond and 115 Partition it was designed for 1-10 barrels. My wife and I own several that shoot it very well, in chamberings from .257 Roberts to .257 Weatherby, but often we had to try more than one powder. Her .257 Roberts really likes Ramshot Magnum, while my NULA .257 Weatherby likes Reloder 25.

In fact I learned about Magnum with the 120 Partition from Doug Phair, who owns Western Powders. He suggested 51.0 grains, which gets about 2950 fps in her rifle.

When I rebarreled a .260, I ordered the 1 in 9, then began reading how I should have ordered 1 in 8. Still wish I'd have gotten the faster twist, but it shoots 129 grain Hornadys (interlock and interbond) very well, and they're good enough for me. This summer I found two boxes of Sierra 130 grain Gamechangers, and bought them before I checked the website and found they need at least a 1 in 8 twist. Didn't even try them, traded them off for more Interbonds. I did open one box....looked like I could have used them for fenceposts...those were long bullets!

When bullet companies recommend a twist-rate for a bullet, they list the twist required for the "worst" environmental conditions, especially low elevation and cold. The same bullet will often stabilize well at higher elevations and in warmer temperatures.

I owned rifles in various 6.5mm rounds for many years, all with 1-9 twists, and never had a problem because just about any bullet (even the very long 140-grain Bergers) would stabilize in my part of Montana, where the valley is 4000 feet above sea level, and much of the hunting is at 6000-8000 feet.

I think that greater than the length of the Berger 115 you start to loose some of the BC but it will still shoot well. A 1-9 handles everything up to 120 grains but I wish I had gone faster now that there are a couple of 130s in 25 caliber.

What I am not understanding is the loss of stability when the bullet goes sub sonic. Is it because of the sonic boom effect, or is it like a physical barrier, or something else?

The nature of the airflow around the bullet changes when the shock wave goes away. The transition isn't as smooth as above and below Mach 1.

The term used is "transonic," because that's where the instability tends to occur, due to during the transition between supersonic and subsonic. Sometimes it doesn't occur, but even if it does some bullets become stable again.

The same thing happens to fast jet airplanes. As once sources puts it, they must not only deal with the shock wave but "air moving faster than sound over parts of the wing and slower in other parts. This obviously can affect bullets as well.

Mule Deer, thanks for the input. Maybe I should have tried those Gamechangers! My elevation is from 2000 ft to 3500 ft on the divide (Big Sheeps) , and I do go out in the cold once in a while, so I probably wouldn't have had great confidence in them even if they shot well in the summer. But I got a good trade on them, didn't lose more than the price of a couple beers, so went with the trade and the known bullets. I've shot 140 grain Rem factory ammo too, and they shoot well. I really like the Hornady 129s though, shoot the interlocks for most things and practice, the interbonds for serious deer hunting. Someone once wrote in an article that finding a cheap practice bullet that substitutes for the more expensive bullet is a good plan (thanks for the idea) and it works well for me.

300 savage,

The Big Sheeps are very interesting country! Have hunted them a little, but years ago also worked for an archaeological research firm that did a survey on the BLM land. Among other things we found an old, fired, "inside primed" .50-70 Springfield case, which just might have been hanging around since the last of the buffalo hide-hunting days of the 1880s, when that was the last area where a big herd existed.

One other reason the 130 GameChangers might have worked is that while they're long, the plastic tip doesn't count much in stability, because it's so light. Which is why some twist-rate formulas indicate some plastic-tipped bullets won't stabilize--but do. The one twist program I've found that includes an "input" for plastic tips is JBM's, www.jbmballistics.com›cgi-bin jbmstab-5.1.cgi

Thanks for the link! That is some interesting history. Up untiil around 60 years ago, my dad said that you could find the occasional buffalo skull. The last one he found, in 1962, is in the Glendive museum. I didn't know we had the last of the big herds! I've read that they were named for Audubon Bighorn sheep, but have never seen evidence.

My dad, born in 1921, saw his first deer, a mule deer, in the 1940s. Apparently the homesteaders had shot them out, but they repopulated.

Yep, early homesteaders, prospectors, and ranchers did essentially eliminate big game in a lot of Montana. In fact, the "woodhawks" who lived on the major riverbottoms (such as the Missouri) and cut wood to feed the early steamboats largely eliminated the whitetails which had been abundant along the river when Lewis & Clark came through, both by meat-hunting and cutting down the timber. Which is where the myth (popular in the 1970s and 80s) that whitetails were "invading" the west came from. Instead they were just re-inhabiting their original country--after the timber regrew and humans quite market-shooting deer.

My father's parents homesteaded in central Montana around WWI, and standard procedure was to kill game to eat and protect crops. There weren't many deer (and almost no antelope) until after WWII. In fact my father could remember the first antelope seasons after the war, when apparently tags were often traded for cash or goods, as the tags were considered legal tender.

Thank you for the interesting history!

My barrel is 1-9, I didn't know then what I know now. I pretty much only shoot 140 Sierra game kings in it.

I have a Lilja barreled 25/06 1/10 twist. Our rifle range is about 5600' It shoots the 115 Nosler Ballistic Tip extremely well. Also shoot 120 Sierra H.P. almost as good. Years ago when my son was just starting to hunt and my 30/06 had too much recoil for him, I bought a Ruger 77 in 25/06 and loaded it with 120 Sierra H.P. He killed his first elk with that rifle . That was over 40 years ago. He has his own bunch of rifles now, but still uses that old Ruger to hunt with. ----Probably just sentimental, but also damn efficient.

Dennis,

I missed this post somehow. ELR shooters deal with bullets dropping to transonic velocities, the cause of the long-range instability.

The spitzers and loads most hunters use never drop to transonic velocities.

Is there a similar effect as a bullet transitions Mach 2 or 3 ?

I don't believe so. Basically, once you're going fast enough to push a shock wave you can keep pushing it even faster.

I was thinking in terms of the bulletin decelerating through Mach 2 or 3 at various distances down range.
I keep reading about accurate velocity nodes, and wondered if Mach transition could be a detracting factor ?

That has to do with mechanical barrel dynamics, and IMO it's actually more of an exit timing phenomenon than simple velocity.

I’ve certainly observed the transonic degradation effect on accuracy with .22 LR, by increasing target range from 75 to 125 meters. As I recall one High Velocity hollow point ‘s accuracy fell off at 87 meters, where it had been quite accurate up to that distance.

I was just wondering if anyone had observed this Sort of thing in the context of Mach 2 or 3 transitions.
Or am I wildly off base again ?

There is nothing overly special about various multiples of the speed of sound, but when a bullet decelerates through the trans-sonic zone the sound waves comprising the "sonic boom" start to keep/catch up with the bullet and disturb its gyroscopic stability.

Jordan & Mathman et al :

My memory may be faulty, but I recall a Flight Dynamics lecture discussion
( from several decades ago ),
that mentioned a reduced buffeting effect transitioning the higher Mach numbers, Under acceleration.

I also Vaguely remember a warmish stuffy govt classroom after a substantial mess hall lunch, amidst a hectic flying schedule.

Wish I still had the lecture notes that spurred all this.

The notion of this “Trans-Mach” buffeting, and my vivid visualization of this LR/ELR/ULR application has stuck with me though.

My trans sonic experiment with .22Lr was also shot in a longer barrelled heavy barrel.

The same HV ammo was linearly accurate out to 100 -110 meters before fanning out.
As I posted previously, the shorter Barreled sporter rifles accuracy with that ammo fell off at ~87 meters.
Ie accuracy was linear with range out to 87 meters, then an additional factor came into play.

Could’ve also been parallax, or vagaries of the breezes down range I suppose.

There’s a high paying article in this somewhere !
Or at the least, the justification for purchasing a LabRadar setup and other cool kit ! 🥴

Edited my last for Clarity Ref transitioning through higher Mach thresholds

I don't know what causes accracy-speed nodes but they're very real. And some are very abrupt.