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.