Hello there! In our posts from the “Hunting 101” series – aimed at the growing segment of people who, having reached a certain age but knowing nobody who hunts, but still would like to give it a try – we’ve given you a few tips on how to pick your own rifle, and how to be a better shot without spending any ammo. Today let’s get closer to shooting things, and talk about a few things you need to know in order to harvest your game: ballistics.
Ballistics, as far as hunting is concerned, is the study of what happens to the bullet when you fire your rifle. It is divided into three parts:
- Internal ballistics.
- External ballistics.
- Terminal ballistics.
Not all of those are of equal importance, and there are many great hunters who kill their game without thinking much about pressure or penetration. But if you’re like us, you want to know how things work, so we’ll give you the most essential coverage.
Internal ballistics is about what happens in the barrel, from the moment the striker hits the primer to when the bullet appears out of the muzzle. As gunpowder burns, it turns into a large volume of hot gas at high pressure, which pushes the bullet along the barrel, accelerating it to some 2,000-3,000 feet per second, depending on cartridge and loading. At the same time, the twist of the rifling gives the bullet a bit of spin – about 300,000 rpm or so – to keep it stabilized in flight.
The action of pushing the bullet along the barrel meets a considerable resistance in the form of traction, which increases disproportionately the faster the bullet goes. As a consequence, you can’t increase the powder charge indefinitely. After a certain point all additional powder will be spent on fighting the extra friction, increasing pressure and temperature without anything to show for it at the chronograph. From this, you can understand how “Magnums” differ from “non-Magnum” cartridges: the latter strive for the balance of power charge, barrel and bullet weight, the former exceed the optimal proportion to get a little more velocity in exchange for a lot more pressure.
A couple of other things you should bear in mind:
- As the velocity depends on friction in the barrel, don’t be surprised when the first shot fired from a cleaned and oiled rifle will not go to the same point as the second and third. Wipe the barrel dry before the hunt, or fire a testing shot or two, especially at the start of a backcountry hunt or safari.
- The type of the powder must be aligned with barrel length and the weight of the bullet. The rule of thumb is, faster burning powder for shorter barrels and lighter bullets, slower powder for longer barrels and heavier bullets.
Internal ballistic may sound perfectly theoretic, and in fact the R&D departments of gun and ammunition companies have you covered, but it is the major force in one of the most important aspect of a rifle’s performance:
In hunters’ and rifle shooters’ lingo, accuracy is how much does a bullet stray away from its designated course – or, if you want to sound like a pro, how different is the Point of Aim (PoA) from Point of Impact (PoI). In the days of our grandfathers, you had huge boasting rights if you had a rifle that could do one minute-of-angle. That is, the distance between PoA and PoI of each shot did not exceed one inch per one hundred yards of travel. These days rifle and ammunition companies got to where almost any rifle on the market is that accurate, and many do way better.
The accuracy is determined by the following major factors:
- Quality of the bullet: if the bullet is eccentric or damaged, it is likely to stray off its course.
- Spin of the bullet. The twist stabilizes the flight only if the rate of rotation is correct. This comes down to the choice of the bullet weight: a bullet that is too heavy or too light for the barrel of your rifle will not fly well.
- Alignment with the barrel. If the bullet is even slightly off-center, it will deflect in the relevant direction.
- Condition of rifling. If it is worn, the bullet will be more likely to be offset, especially if the wear is at the muzzle, or even damaged, especially as it leaves the case and enters the rifling.
Misalignment of the bullet in the barrel may occur because of overheating. Hot barrels follow the laws of Newtonian physics and expand. A barrel with thin walls will expand more, and the bullet might be not quite as well centered – see why special long-range rifles have such thick barrel tubes? Likewise, barrels that are sloppily made will expand unevenly, compromising accuracy.
External ballistics explains (and sometimes predicts, but that’s not certain) the flight of the bullet from the muzzle to the target. After trigger control, it is the most important part of practical rifle shooting. After the bullet leaves the barrel, it is influenced by two major forces. The first one is the air resistance, which slows the bullet down. The second is the force of gravity of our planet, which makes the bullet ultimately fall on the ground (unless you start it with acceleration of 11 kilometers per square second, then it will fly to outer space, but that’s unrealistic).
The result is – as you probably know – that unless the target is touching the barrel, the bullet will not hit the spot that the barrel is looking at, but will strike some point below it instead. You should aim above the target to hit it, sending the bullet at an arch-shaped, or “ballistic”, trajectory. How much the bullet will drop, a.k.a how high you should hold, is a complicated question, the wrong answers to which have saved more animals than PETA ever will.
The shape of the trajectory depends not only on the bullet’s muzzle velocity, but also on:
- The angle of the flight path to the horizon.
- The current velocity of the bullet.
The first part is important for mountain hunters, because, for example, the bullet sent at 45 degrees angle to the horizon will drop only ½ as much as the bullet that travels the same distance parallel to the ground. Shooting up or down hill, you have to make adjustments. The rule of thumb is to estimate the so-called “horizontal distance” – how far the animal would have been, if it was at the same altitude as you.
The second part explains why the ballistic trajectory is non-symmetrical. The slower the bullet travels, the more it drops, therefore, the closer to the muzzle, the flatter the trajectory, and the farther away, the more arch-like it becomes.
The Ballistic Coefficient
The velocity of the bullet at any point of its travel depends mainly on its shape – or, how well it can withstand air resistance. This characteristic of the bullet is known as “ballistic coefficient” – just like aerodynamic coefficient for cars. You can find the BC for the bullet you intend to shoot in ballistic tables, but bear in mind that it’s only a relative figure, calculated according to a mathematical model, and for just one velocity (air resistance below and above the speed of sound are very different stories). The BC is especially important at longer ranges, 500 yards and more.
As the result, it’s practically impossible to make an accurate theoretical prediction of how much a bullet will drop at a given range, even with the help of ballistic calculators. At short distances (up to 300 yards) the error is usually negligible, but on longer ranges you have to verify the trajectory of any specific rifle-cartridge-scope combination by practical shooting.
The invention of a portable laser range finder revolutionized long-range shooting: to calculate how much a bullet will drop at a given instance, you have to know the distance, which in a hunting scenario is by default unknown. But even with modern rangefinders long distance spells big trouble: The higher the distance, the less room for error.
Let’s assume for example you have a rifle with 1 MoA accuracy, and shoot at an animal with an 8-inch killing zone. At 300 yards, all your shots (not accounting for user error) will still be in the 3-inch circle, so if you miss by 4”, your shot still has a 100% probability of coming true. At 800 yards, your bullets will be landing into a 8” circle – the same as the killing zone – and a 4” mistake will mean 50% chance of a miss.
Even more important is the increasingly arching shape of the trajectory. In the same example, if you’re shooting at an animal you think is 400 yards away, but it’s actually 415 yards off, you’ll still hit the vitals. Make the same mistake at 600 yards – so that the animal is 615 yards – and you’ve missed.
The Big Ballistic Lifehack: Point-Blank Range
When you read about long-range shooting these days, you may be under the impression that the way to go is to sight in your rifle so that the bullet strikes at point of aim at 100 yards, and then, if you need to take the shot at, say, 500 yards, you adjust your scope according to the distance. This is a good idea, especially for those who shoot at unmoving targets at known distances. But hunters have an option which is better for the beginner – sight in for the maximum point-blank range – that is, so that even at the maximum point of the trajectory, the bullet would not miss the vitals of the animal you are hunting.
For most modern scope-sighted rifles it would be something like to PoA at 225-250 yards, and overall at the distances of up to 250-300 yards, you can just hold where you want to hit and let loose. Incidentally, at this distance or closer most of the trickier aspects of ballistics can be ignored. Whatever you hunt, it’s very rarely that you can’t stalk your quarry to 300 yards, so the best idea for a beginner is not to take longer shots – at least, until you get enough practice and are confident you can do it.
Yes, the bullet travels through air, not through vacuum. That means, when the air masses move – a.k.a when the wind is blowing – they may deflect the bullet, especially if the wind blows across the direction of your shot. The faster the bullet travels, and the better its BC, the less it’s affected by wind; the problem here is that lighter bullets that can be driven to higher velocities typically have poor BC. The problem is especially acute when you’re shooting across a valley – the wind is always stronger above the ground, and if you’re shooting across a 100-yard-deep canyon, in the middle of its travel your bullet will be 100 yards above the ground. The way that wind can cause the bullet to strike a few feet from the intended destination is arguably the most difficult part of long-range rifle shooting. Only practice helps; some experts advise to try shooting on open rifle ranges with .22lr rifles at long distances – like, 150-200 yards.
Another thing that many people miss about the ballistics is that it takes time for the bullet to reach its destination. From the moment when your brain gives the command to pull the trigger, until the signal reach the finger, until the rifle striking mechanism is set to action, until the powder burns, until the bullet flies along its arched pathway, and until it strikes the place where it is supposed to, some time will have to pass. When we’re talking about real long-range shooting, like 1000 yards, the flight time alone can take more than a second. This means that, if the animal decides to move just as you’re pulling the trigger, it may be in a completely different place by the time the bullet gets there. Another argument against excessively long shots.
Terminal ballistics covers the somber question of what goes on when the bullet does hit an animal, and whether it kills it on the spot, or only wounds it. Hunters are uncompromising when it comes to killing power: we need the animal we shoot at to drop in its tracks, or as close to that as possible. All other options lead to ethical issues: unnecessary suffering, potential loss of a cripple, and in case of dangerous game, a risk factor.
The two main factors in terminal ballistics of a hunting bullet are penetration and expansion. Penetration means that in order to kill the animal, the bullet must reach its vital organs. With some animals such as buffalo and elephant, non-expanding or solid bullets must be used, because with their thick skin, tough bones, and copious bodies, even these don’t always reach the vital organs. Expansion helps the bullet create a bigger wound channel, and destroy more tissue, resulting in quicker death.
Understandably, the two parameters work against each other – a bullet that expands too much may stop before it reaches the vital organs, and a bullet that penetrates excellently can just pierce the body, leaving a narrow wound channel that will not kill the animal on the spot; the animal would also bleed less, which complicates finding the cripple by blood spoor. Premium hunting bullets are built so that the head part readily expands, while the rear retains its mass for proper penetration.
Another problem with expanding bullets is that they expand differently at different velocities. Short, fat bullets work more predictably on game than thin, long ones, but thin, long ones typically have a better ballistic coefficient and fly better. As always, it’s a matter of compromise – but in any case, the main factor in terminal ballistics is a hit in the right place.
The Bottom Line
The world of ballistics can be an exciting adventure, but a beginning hunter is advised to play it safe. Start with a rifle chambered for a “regular”, non-Magnum caliber, but with a decent starting velocity, and sight it in for the maximum point-blank range. For hunting, pick the ammo with the best bullet you can afford. Learn how to hit targets at long range (here’s a blog on the subject), but try to keep your shots within the point-blank range. Above all, good hunting!