In one of the previous “Hunting 101” posts, we talked about rifle ballistics. Now it’s time to do shotguns, and believe me, shotgun ballistics is an even more wonderful and mysterious topic. Follow me!
Terminal ballistics
For shotguns, we’ll reverse the usual sequence, and start with terminal ballistics – that is, how a shot charge kills the animal. Then we’ll cover what happens on the way from the muzzle to the target – or external ballistics – and finish with internal ballistics, the processes that take place inside the barrel.
That’s because there’s a world of difference between shooting a single projectile a.k.a. bullet (whether from a rifle or from a smoothbore gun) and shooting a charge of small pellets a.k.a. shot. With a rifle, we must put the bullet into exactly the right spot, and killing is a question of precision. With a shotgun, the shot charge is spread over a large area, and killing is a question of statistical probability.
How many pellets does it take to kill a bird?
One that hits the right spot should theoretically be enough. But as you already know, there’s no way to control the flight of a single pellet. That means as many pellets should strike the bird, so that statistically at least one of them hits the vitals. With most birds vitals make about a third of a body’s cross-section, so the minimum number is three. To be on the safe side, make it four or five. It goes without saying that the pellets must have enough energy to penetrate the vitals. But don’t overdo it: a bird with about a dozen solid body hits will usually be too damaged for eating.
In the real world, things can get complicated. A bird may receive several pellets to its body and still be able to fly, run, or swim so far that only an epic performance of the retriever can secure it. On other occasions, you could kill a bird stone dead, even if none of the pellets penetrate the skin – if there are so many hits the bird dies from sheer shock. Such incidents gave birth to many a shotgunning myth. But statistically they are outliers that get more attention than they deserve, simply because they make better campfire stories.
What does make a big difference is the stuff that the pellets are made of. Unlike rifle bullets, shotgun pellets all come in one shape: a ball (some ammo makers try to experiment with other shapes, but mostly their benefits don’t justify the increase in price). And here the density of the metal that the pellet is made off is all-important, but this is a question of external ballistics.
External ballistics
External ballistics studies the behavior of projectiles on their way from the muzzle to the target. Most parameters that are of utmost importance for rifle ballistics hardly matter for a shotgun. Accuracy is abstract: shot pellets are not even supposed to all come to the same POI. Trajectory is unimportant: shotgun pellets lose steam long before the drop begins to matter. What matters is pellet velocity, and the “pattern” – the volume and density of the shot spread.
The shot leaves the muzzle in a formation that is so tight it works like a bullet. In fact, if you fire a slug and a shot charge of the same weight at a log from the distance of three to five yards, you’ll see a similar penetration picture. But as the distance increases, pellets start to spread out. And continue to spread out until the distance between individual pellets becomes so great, that a hit is nothing short of a miracle.
Obviously, you don’t want the spread of your pattern too wide, or you will only get cripples and misses. But you don’t want your pattern to be too tight either. Not only can it lead to the bird being “plastered” – so damaged that you can’t use it – a narrow killing circle makes it hard to connect with the bird. Hunters who pursue such upland game as ruffed grouse and woodcock in dense undercover go to great lengths to get their guns spread the loads as wide as they would go, sometimes with the help of “spreader” loads and rifled chokes. In other words, you want your pattern just right.
How do I know if the pattern is the right one?
Here we come to what in shotgun lore is called “patterning”. In short, it means shooting at a target – the gold standard is at a 30-inch circle at 40 yards (or a 750-mm circle at 35 meters) – and counting the hits. What percent of the pellets are inside the circle is the most important parameter of the pattern.
In a good pattern the pellets are evenly distributed across the target, without holes or “constellations”. It is all right if there’s a higher concentration of pellets in the center of the target, it means the load is likely to be effective even at a longer range. It doesn’t hurt to divide the target into areas that are as big in area as the silhouette of the bird you’re after, to see how many pellets land in each area.
Muzzle velocity can be measured with a chronograph, but for target velocity it is problematic. How fast or slow the pellets are as they reach the target is measured indirectly, by estimating penetration into a material of known resistance, such as a paper or cardboard block. An advantage of this is that it doesn’t only measure the velocity of the fastest pellets, but of each pellet in the load.
This is important because you want the velocity of the pellets to be consistent. If some pellets reach the target much faster than others, it means the pattern spreads too much from front to end – in shotgunning known as “shot stringing”. With too much shot stringing, the pattern becomes less dense, which, coupled with lower energy carried by slower pellets, reduces the probability of a clean kill.
Pattern is a matter of balance
There’s no such thing as a shotgun pattern that is perfect for any hunt. A proper pattern is a matter of compromise, that depends on many factors, including the type of ammunition, the size of the bird, and the most likely distances of the shot.
For example, if your distances are close, you can select a smaller shot size that would allow you to have a wider spread, to make hitting easier. If you need to shoot at the maximum ranges, you might have to go for a larger pellet size, but would have to pick the choke that would give you a tighter spread. But this way you’ll sacrifice the killing circle, and would have to shoot more accurately if you want to kill your birds dead and not leave any cripples.
The shot problem: Toxicity, density, and velocity
Shot pellets for shotguns have been traditionally made from lead, but due to environmental concerns and regulations, especially regarding waterfowl hunting, alternative materials like steel, bismuth, tungsten, and others have become more prevalent. Each material has its distinct properties affecting ballistics, effectiveness, and suitability for different hunting situations.
With higher density materials such as tungsten, a much smaller pellet will have the same weight as a much larger pellet of a lighter material, such as steel. These two pellets, starting at the same muzzle velocity, would also have the same muzzle energy. However, a denser pellet will face less wind resistance. So, as it approaches the target, at a distance of say 40 yards, it will be traveling much faster, and carrying much more energy.
The hardness of the shot material also plays a role in how the pellets pattern and penetrate targets. Harder materials like steel retain their shape better than softer materials like lead. So they are less likely to be damaged as they travel through the barrel. However, a harder material can damage a barrel of an older shotgun not intended to be used with it.
Internal ballistics
As in any firearm, the shot charge is accelerated by pressure of the gas that is created as the gunpowder burns. The main part of the shotgun bore, between the forcing cone and the choke, is shaped as a cylinder. Nothing really exciting happens there, except that the shot charge accelerates. Modern ammunition makes barrel length relatively unimportant, although 28” to 30” are the best choice for most shotgunning. It’s the forcing cone and the choke that make or break the patterns.
Forcing cone
The forcing cone in a shotgun is the tapered section of the barrel that transitions between the chamber (where the shotgun shell resides when fired) and the narrower bore of the shotgun barrel. The producers of old tended to make this part rather short and abrupt, which helped to get better results from the not yet perfect ammunition of the day.
In modern shotguns, forcing cones are longer and more gradual. That reduces both recoil and deformation of pellets, resulting in fewer flyers and a more consistent pattern. Some companies make their forcing cone design the tour-de-force of their advertising campaigns, but any reasonably long and properly designed forcing cone is as good as another.
The choke
The choke bore, or simply “choke,” refers to the constriction at the end of a shotgun barrel. Its primary function is to shape the spread of the shot as it exits the barrel. It does it by changing the direction of the flight of the side pellets, turning them towards the center of the pattern. Many authors explain it with the garden hose metaphor – if you’ve ever watered the plants or washed the car, you know that if you press the end of the hose with your fingers to make the exit hole narrower, the water will come out faster and reach farther.
Most designations of the chokes are relative and rather abstract – they range from a “Cylinder Bore”, which means no constriction at all, to “Full Choke” – a maximum constriction that can safely work with any shot size, with intermediate steps such as “Improved Cylinder”, “Modified”, “Improved Modified” in between. There are also special variants. For example, Extra Full or Turkey chokes are even tighter than Full chokes and are designed for maximum pattern density at long ranges, while Skeet chokes are designed to provide a wide pattern at short distances for skeet shooting.
In general, the tighter the constriction, the narrower the shot spread, and vice versa. However, just how tight the choke needs to be – that is, how narrower the muzzle is in relation to the main bore section – depends on many factors. Those include the length and shape of the constriction, and the type of ammunition.
For example, a shot cup acts as a cushion, making the transition of the pellets smoother, and the pattern can be 5 to 10 per cent tighter than without a shot cup. Bigger pellets, such as B and BB, tend to perform better with longer and smaller constrictions, while smaller shot like #7 tp #9 (like with shotgun gauges, the smaller the number the bigger the pellet) can work its way through tighter chokes with excellent patterns.
Even more important is the stuff the pellets are made of – harder materials like steel require less constriction as softer lead pellets, so a full choke for steel and a half choke for lead often have the same exit diameter.
What determines the good pattern?
In short, a good pattern depends on the transition of the shot column through the barrel. The smoother it goes, the more even and harmonic the outcome. But if we force the shot charge to go through the constrictions that are too steep for it, or if the pressure is too high, then bad things start to happen.
Some pellets may get deformed. Others jam against each other, and strike each other off the true course like billiard balls. Sometimes their collisions lead to a pressure hike, like accidents on a highway lead to traffic jams. That can be dangerous for both the shotgun and the shooter.
The bigger the pellets in relation to the bore, the more likely they are to jam and push each other aside. The smaller the pellets, the better they work through the chokes and forcing cones. Another distorter is the jet stream of the residue pressure that, if too high, can scatter the pellets just as they leave the barrel.
And last but not least, you can only give the pellets so much velocity. After a certain threshold, velocity will ruin the pattern, and you’ll lose more killing power than you’ll get from extra speed.
The bottom line
While shotguns might not have the long-range precision of rifles, they offer a unique advantage in hunting moving targets across shorter distances. The key to wingshooting lies in understanding the spread of your shot and choosing the right choke for the distance and size of your target.
But patterns only matter when you do your part. Many years ago my grandfather told me, as I tried to blame the gun and ammo for my poor shooting: “When you keep getting cripples, or when you keep plastering birds, then there’s something wrong with your patterns. But if you keep missing – it’s not the gun. It’s you.”
And he was right. If you’re shooting ten feet from where the bird is, it doesn’t matter a single bit whether you’ve got the best patterns or the worst patterns in the world. The most important part of shotgun ballistics is knowing how to hit the birds!
