Many years ago I thought to myself, I'd be happy if I could place accurate rounds onto a target with a high hit-probability at 1,000 metres (1,093 yards). It seemed like a long way to shoot and the thought of being able to do it excited me.
At the time, I had no clue how to make it happen, I just knew that I wanted to. I'd been shooting for a few years, handguns and hunting with rifles and shotguns, but shooting at long range wasn't something I'd done.
It wasn't long afterwards when my training began, a lot of theory and equal measure of practical work, and I soon began to realise that 1,000 metres wasn't that far at all...provided one had the right ability, skills and understanding when it came to the elements required for accurate long range shooting.
As my training progressed, and those three things began to settle on me, I came to understand that shooting at well over twice that original 1,000 metre range was within my capability...but there was much that occurred between being unconsciously incompetent at the very start to unconsciously competent at the end...although the end hasn't happened yet because I'm still alive and still learning to this day.
I've written about and explained so many concepts around long range shooting over the years, here on Hive and in other less social-media oriented places, and thought I'd introduce another concept today. You can read my last long range post here and at the bottom of this post I have linked a few more but today I'm going to introduce a phenomenon called, aerodynamic jump.
What is aerodynamic jump
There's many factors that can cause a projectile (bullet) to deviate from it's intended path; gravity of course, striking something in-flight like grasses, twigs and so on and spin drift (as per one of the links below) just to name a few. However in long range shooting the operator needs also to consider aerodynamic jump which can effect precision (through bullet dispersion) downrange.
The idea of precision shooting is that the projectile maintains a trajectory that follows the centre-line of the bore as it leaves the muzzle and heads to the target. However, sometimes a projectile leans up or down or to either side (yaws) as it exits the muzzle and that's when the phenomenon of aerodynamic jump exerts itself causing the projectile to jump out of that centre-line of the bore and to a different (random) trajectory.
That initial yaw is often caused by cross-winds, issues with a non-symmetrical muzzle or muzzle brake which are often asymmetrical if a cheap and nasty one has been fitted. Often, precision rifles have crowned muzzles to protect the rifling which has to be kept in perfect condition; the crowning protects it from knocks and other such accidental damage that can occur in the field and which effects the projectile as it leaves the muzzle. There's other reasons for the yaw but I don't want to get complicated.
Another factor is dynamic bullet inbalance.
The problem is that an unbalanced bullet exits the muzzle wanting to rotate upon an axis at a different (and random) angle from its geometric axis meaning it yaws, (tips) and jumps randomly to a new axis as it exits causing bullet dispersion downrange. The direction of that yaw is unpredictable so instead of hole-in-hole results on the target, the shooter is left with random results, if it hits at all. Sure, the shots may all be in a reasonable group on the target set at 100 metres, or even 500 metres, but small margins become large margins the farther the bullet flies and when precision is required bullet dispersion is unwelcome.
The work around
This situation is not necessarily easy to predict and mostly is impossible, certainly in my understanding of it. I am just the blunt instrument who fires the shot though, not the smart-ass boffin behind the scenes in a science lab. The projectile's geometry, rate of spin and its distribution of weight are all ways to deal with aerodynamic jump and that's why so much effort goes into the testing and design of projectiles designed for long range accuracy, predictability and repeatability. (Most projectiles are developed with aerodynamic jump in mind however it's at long range where the effects are most devastating to accuracy, precision and hit-probability.)
There's a measurement called sensitivity factor that is used to determine how sensitive a projectile is in respect of aerodynamic jump, which some smart-ass boffin came up with. A low jump-sensitivity-factor is good, a higher number is bad. Simple right? With this in mind projectiles are developed to minimise the effects of aerodynamic jump, and shooters like me spend hours and hours developing the right load (bullet/powder/amount of powder) and make our ammunition according to what we find throughout the load development research to deliver the best results down range.
The twist
If you're not aware, rifled barrels have what's called a twist rate which is how many inches of barrel are required per turn of the bullet as it travels along.
My culling rifle for instance, Tikka CTR .243, has a 1:10 twist rate meaning a bullet fired down the barrel will spin one revolution for every ten inches it travels; that's a pretty fast spin in rifle terms. The thing is, to combat aerodynamic jump, bullets need to be spun at certain speeds to stabilise them; the longer the bullet, the faster the spin needed. (Also, as an aside, imparting spin to a bullet is done for better accuracy generally that's why rifling was introduced to barrels back a long time ago.)
For long range shooting, longer (and heavier) bullets are used and they also have a higher ballistic coefficient (BC) which leads them to perform better as they deal with the outside forces acting on its flight.
Just so you know, BC is a measurement of the projectile's capability to deal with resistance in it's flight, the resistance provided by the atmosphere.
Again, using my culling rifle system as an example, the Hornady V-Max 87gr projectile I use (pictured in this post with the orange tip) has a BC of 0.196 using the G7 drag model and it has a gyroscopic stability of 1.34 which is considered good. It's a fast spin, the bullet stabilises immediately on leaving the muzzle and it's trajectory is true and correct which makes it such an accurate rifle/ammunition combination.
Anyway, with longer projectiles a faster spin-rate is required and that's why, when I'm developing a load (determining what bullet, gun powder and gun powder quantity to use), I test many different combinations until the right one is found. What works for an identical rifle may not work for mine for many reasons and the projectile itself, type of powder, primer, seating depth, neck tension and other factors also play a part.
Someone in my last firearms post (as linked above) laughably mentioned the use of a 30-30 calibre for long range shooting; clearly someone who has no idea.
The thing is, that the projectile on that calibre is only stable to a certain range and after that begins to destabilise (tumble often) making it almost useless. It's at around 228 metres that it begins to destabilise then its accuracy falls away and the energy it is capable of imparting to a target is insufficient to kill effectively. It's a great hunting round out to about 200 metres and has done a great job since about 1895 but for long range shooting...well, it's never going to do the job when a shot is called for at anything past a couple hundred metres.
I mention that to demonstrate the importance of gyroscopic stability in long range shooting and the importance of dealing with aerodynamic jump.
Eliminating some of the contributing factors like imprecise muzzles, damaged rifling at the muzzle and asymmetric muzzle brakes helps, and understanding twist-rate then using a precision-made projectile with a load designed to match the rifle it is being used in will help mitigate the effects of aerodynamic jump and bring the shooter greater precision and hit-probability through less bullet dispersion. Of course, it's not the only reason for imprecise shooting, just one of the reasons, each have their own ways to mitigate the effects.
There's so many factors that can cause a shooter to miss downrange whether it's 100 metres, 1,000 or 1,500 metres and more. It's all about small margins, science, shooter skill and the understanding of the concepts that come together to get a shot onto a target. Aerodynamic jump is something a shooter can work around for certain, however it's difficult to totally eliminate, if that's even possible...Again, I'm not a smart-ass science boffin. I shoot well though, and getting rounds on at well over 1,600 metres is something I've worked hard to learn over the years.
Looking back at the person I was back all those years, thinking that 1,000 metres was a long way, makes me laugh these days considering what I can do now but it's been a great journey and I'm happy to have built these skills which have served me well over the years.
Feel free to ask any questions, but if you're a smart-ass science boffin you probably already know more than me about the science stuff...you can ask about the shooting though if you like. This is not designed to be a text fully explaining all the complexities of aerodynamic jump, gyroscopic stability, projectile manufacture, load development or anything else; it's just a light introduction to the concept, but I'm happy to answer any questions you might have.
Design and create your ideal life, don't live it by default; tomorrow isn't promised so be humble and kind - galenkp
[All original and proudly AI free.]
As stated above, here's a few of the many posts I've written previously about long range shooting: Supersonic and Transonic, Free Recoiling, Some Basics, Spin Drift, Cold Bore.
All images in this post are my own.
I remember when I was in the Army, a guy mentioned a recruit who had an episode, sawed the end off his F88 Steyr and tried to go on a shooting spree but missed everyone.
From what I recall (many decades later) he claimed that the barrel and round have a resonance; so the barrel wobbles from the explosion, and that the length of the barrel is engineered so that the round exits mid-wobble and goes straight. You'd need to shorten the barrel to a specific length, to prevent the round landing either way too high, or way too low.
Even as I'm typing this, I'm thinking it doesn't make a lot of sense.
NB: I was 17 and he was much, much older, like 20.
It's called barrel harmonics.
So, as I say in this post, load development is carried out to determine the right load for the rifle, the most accuratand repeatable one. Barrel harmonics come into play. It's not really about wobbling I guess, but there is certain movement. Imagine a hose laying on your lawn. When you turn the tap on full it snakes around. That's a very extreme example of course.
Basically the barrel vibrates which is why, for long range rifles, barrels tend to be thicker and heavier. (not always the case though. A load must be found that best deals with that vibration.
Sawing off a rifle barrel is not only stupid, but will totally screw up the spin-rate (will be too slow) so the bullets won't do anything close to what they are supposed to and will probably start tumbling quickly. It would still be deadly at close range though. Accuracy would be terrible.
All my long range rifles have fully floating barrels so they are permitted to do their thing independently of anything else, touching other parts like the stock - This allows me to create a load that best deals with it (accuracy down range) and I know it'll be repeatable.
Nice, removes a lot of variables. Don't want a change of scope to throw everything else out.
Changing scopes means re-zeroimg of course, also a box test on the scope itself, but it doesn't have an effect on the projectile itself.
Out of curiosity, you have any idea how altitude/elevation affects aerodynamic jump?
So funny I started reading your post and the first few paragraphs, and then started thinking "well yes Galen, but what about twist rate" and then of course when I scrolled down there it was. Twist rate came to mind for me because I learned the lesson the hard way a few years ago. I was working up a load with my .338 Lapua magnum. I had shot some good groups and sighted in with factory ammo, which I often use to get the brass needed for reloading. I was so proud to have loaded up some hot rounds that were sending a 180 grain projectile at over 3,500 fps. They were consistent on the chronograph, with very little (mostly single digit) deviation. I went out to the range to show a buddy how accurate they were, knowing I would need to adjust the scope a bit for the different weight and speed. I was quite embarrassed when my prize rifle was shooting all over the place, instead of the quarter or nickel size groups I had been bragging about.
I mean even at just 100 yards, I was lucky to have 1 or 2 shots stay on a piece of 8 x 11 inch paper.
I had a lot of difficulty getting the scope adjusted. It just wouldn't seem to hold zero. First I thought it was loose, then I thought it was broken. I removed the scope, I remounted the scope. I finally even sent the scope back to the factory for repair. (They cleaned it, but it wasn't broken). I put a different scope on the rifle, same problem.
So now some 200-300 rounds later, I decided to change it up a bit. I remembered that the original factory loads were 250 grain instead of 180 grain I had handloaded. I ordered some 250 grain bullets and some 300 grain bullets, loaded them up and aha! Back to nice tight groups. It seems the barrel length and 1:9" twist on that rifle did not like the lighter 180 grain bullets at all. I'm now shooting the 300 grain at about 2,600 fps. The ballistics and what would have supposedly been a very flat shooting bullet in the 180 grain, was useless given the wide scatter. If I were inclined to regularly shoot the 1,000 or 2,000 with this I would probably try the 250 grain, but I just don't have the place here to do that yet. I've settled on the more accurate 300 grain and the handy Strelok app to help with the distance, given my primary use is usually under 500 yards.
I've seen this with others that would sometimes even sell their rifle thinking it was inaccurate, when all it needed was change of diet.
Well, and a pic, cause who doesn't love to look at a Lapua?
This is a great example indeed and I've known others who have had similar issues. Making the right projectile choice is critical and while playing around with others can be fun there's often consequences, as you found out.
Who wouldn't want to have a 180gr projectile pushed at 3500fps! But without accuracy one might as well throw a rock whilst wearing a blindfold.
Spin-rate is critical...well, everything is critical to precision shooting really. It's this aspect of shooting that deepens the enjoyment aintbink, the science behind it. A person could shoot for fifty years and not understand these concepts because they don't really need to at short ranges but as the range extends, so must ones understanding and knowledge.
I'm glad you got that round sorted out...a fine looking rifle too. I'd like to have a go behind it.
I have indicated on several barrels that were damaged or poorly designed, and cut a radius into the end; and changed the rifle all for the better!
I'm messing with an old LaBelle, and due to similarities; I may convert it to a 30-30. You speak truth on the ballistics on this round. I kind of group it with the ak and Enfield rounds. They seem to behave a lot alike (even though the Enfield is my Son's favorite rifle) and seem to be more for limited ranges, less than 500 yards.
This does Not mean they are inferior, just different. I have several 30-30 (30 calibre with 30 grains of black powder originally), and enjoy shooting both! The original black powder round would have been even more under powered....
This article added a variable I didn't know about, thanks! I wonder if there is a spin balance for ballistic points, to pre test projectile balance before re-loading?
Hey mate, thanks for commenting.
Some of the enjoyment I get from firearms has nothing to do with the actually shooting but the science. Of course, the science is required to make the shooting achievable but it can be fascinating right?
I'm not one to play around as much as you, I don't have the equipment or know-how, but I know people who do and we do our share of messing around with interesting results...none I can say here.
Good question on the spin balance. I can only assume that some smart-ass science boffin has that sort of equipment to hand. Might be something interesting to research.
It would be a way to check manufacturing problems on the points. From the twist (you said a twist of ten) and the velocity at the muzzle, you would have the rpm. Testing it by spinning maybe 10% over that number would allow you to sort out the bad ones.
Some of the harmonics are related to stretch on the barrel as the bullet accelerates, so the heavier barrel resonates less.
Give those sick people my email, and we can talk about crazy things. I also spend more time messing than shooting because I need to be close to her, in case she has problems.
Science has always owned me, and a few times; I've been lucky and owned science! Several patents resulted....
👍💗🤠🎉
At the speed of the bullet for such application, every minor unbalance gets amplified a lot.
At physics course during engineering degree we had a problem like that, calculating the deviation of a bullet according to gravity, air drag force (and its equation depending of speed) and the actual maximum range at certain air densities.
Nice understanding the impact of such factors!
Long range shooters like me don't always fully understand the actual science behind it, but every one will understand the effects these things have on the trajectory/hit-probability/precision and so on. One can't do the job without understanding and knowing how to work around it.
I had never heard of this. I love these techy gun posts for just that reason. Must be a bugger when you are locking up the 'perfect' shot and it happens!
It's all fun and games and despite being a pursuit of precision is often imprecise...there's ways around that too, but making sure all the factors have been addressed, mitigated or prepared for ahead of time is the best way to go.
It's always good when you can look back at a thing that's easy now and remember when it was really hard :)
Yeah, it makes the work and the effort worthwhile.
A well written knowledge of how projectiles launched. An attention to detail surely a great step to expertise.
Thanks for taking a read about aerodynamic jump and the other concepts I mention in this post, I hope my explanations were easily followed, although I left so much out to make it somewhat readable that it's probably not all that clear.
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