How to choose shotgun cartridge

In a book from the time around when the primer was invented gives an old forester good advice to a young hunter: if you hit with more than five pellets have you shot too close to or loaded with too much pellets, if the pellets pass thru - you have used to big pellets.
A simple and fairly concise advice, we are now 150 years later probably should give some thought about.

Most people choose rifle ammo very carefully, they test firing range and sometimes in different media to see how the bullet behaves at impact. From this they then make their choice. But when it comes to shotgun cartridges are often routinely chosen from what the dealer has in stock for a reasonable price.

In the case of shotgun hunting there are three parameters to take into account, the weapon (especially its choke), ammunition design and construction and ammunition charge load. Our predecessors in the field who were hunting on flintlock or percussion time had really only two parameters: pellet size and weight of the charge. So holds the rule above even today?

Pellet size and impact energy

Jan Åkerman states in his excellent book Jägarens vapen ( The shooters waepons) the following values; for the one pellet: 0.11 kgm (1.08 Joule) for birds and smaller game, 0.22 kgm (2.16 Joule) for larger birds and larger game. Gerald Burrard use  approximately the same values in his book; The modern shotgun, vol III the gun and the cartridge.
They are both based their conclusions on the same survey. So one should not be surprised that they came to the same conclusion.
If we make the assumption that most of Shotgun cartridges for lead or bismuth has a muzzle velocity around 400 m / s we get the following table.

This is the rather dry facts. Never mind that the information itself comes from the evaluation of several thousand shots in the game, but what does that say? I have shot several hundred hares during my 25 years of shooting, and done so with everything from US3 to US8. My experience is that US6 is sufficient to game of size and weight of hare over 30 yards by a wide margin. The same goes for goose. For Pheasant, partridge, wood pigeon, it is sufficient with a good margin with US7 the normal shot distance, up to approximately 30 meters. Further out  you can go up to US6. If you have even pattern and pattern density over 35 meters that is. The motto is simple:

Pellet pattern quality is unusable long before the individual pellet energy is too low.

The British have a saying that you must have at least 100 pellets in a 30 "(76cm) circle to have a relatively high probability of dropping the pheasant dead in the shoot. And they use as a rule English size 6 to the pheasant, which is a cartridge with a 2.6 mm pellets i.e. between one and a US6 US7. Recent evidence shows that you get better results with English size 5, i.e. almost the same as a US6, at the longest shooting distance. And if you look at the table above gives US6 adequate performance up to about 40 meters in terms of energy for all small game. US7 is on the limit, but if you hold back a bit on the shooting distance is sufficient even US7.

But how to test striking energy? Energy for the pellet depends on two factors: speed and pellet weight. The problem with measuring the chronograph is that measurement results are quite varied. Measured in series of five shots of the same cartridge, it can turn at 25 m / s or more in speed between shots. Then comes the risk that you shoot chronograph, the one who measures the speed of pellets must live with the fact that it is not a question if but when you can add the chronograph in the list of game you have shoot. And to measure the speed and then draw conclusions one need to compare the cartridge to another with the exact same pellet size of exactly the same material.

And you can also not rely on the size of a pellet in a given US numbers are. In addition; the weight of the pellet of lead depends on volume and density, see also the size of pellet.

And you can also not rely on the size of a pellet in a given US numbers are. In addition; the weight of the pellet of lead depends on volume and density, see also the size of pellet.

Different manufacturers use different materials to alloy with lead in order to get desirable characteristics. Pure lead is generally too soft to work well as pellet. So even if you measure the pellet diameter, the weight may vary some.

Then there was another method that was used before the electronics era: setting up a number of cardboards (with a minimum distance of 5mm between each slice, otherwise the cardboard sheets are packed together and then you get uneven test results) and see how many of these the pellets can penetrate . If you have access to an almost infinite number of cardboard, this is a safe and accurate method that provides an answer regardless of pellet size, weight or speed. But now they have generally no access to an infinite number of cardboard the exact same material. And we usually have much less opportunity to measure the exact temperature, wind or humidity.

So if the chronograph gives a little uncertain answers and the traditional method is tedious and difficult, what do you do? Well it always wise to start from a reference cartridge that you should opt for maximum even performance. I use Eley Impax / Grand Prix, but that choice is free as long as the cartridge in question is performing consistent results in the current weapons. And then you start to shoot one or two shots to the reference cartridge in the test media you have access to for the day, then you only need to count the number of penetrated pages for each shot, and divide each cartridge results with the results for the reference cartridge. The ratio greater than one penetrates it more, it becomes less penetrating the smaller. And choose reference cartridge pellet size at about the same size as most cartridges you should test and you can see pretty quickly in which way it leans.

I have tried this a few years now and it gives very consistent results, much, much smoother than the chronograph. And regardless of the cardboard I get hold of, no matter the weather. Given that each test sequence is performed by exactly the same paper for all the shots in the test. An old CD rack from IKEA works well to put cardboard squares in, they will then be quite small (125 xx125 mm) so you have to be very careful that you get the rack straight down shooting direction. The ambitious makes a similar device for the larger cardboard disks.

Number of pellet in the game and pattern

We can now take on advice in the beginning; a maximum of five shot in the game, with enough impact energy of each pellet. Now we will therefore go from five pellets from the wild body to a combination of shot weight and choke.

If we stick to our 75 cm circle at 35 meters, which is the current size of the surface to measure the choke on, it becomes a little easier when we choose the density (ie number of pellets in the hit picture – pellet per dm²).

Burrard and Åkerman, enter the following as a guide in terms of number of hits in the vital part of the game:

And if you then look at the area that each game has a vital hit area

A 75 cm circle has an area of 44 dm². Within this area we must have three pellets / 0.8 dm² to provide a relatively safe match for a pigeon. It gives 3 / 0.8 = 3.75 pellet/dm² and 3.75 x 44 = 165 pellet of pellets on target within a 75 cm circle at 35 meters with a minimum of 1.08 joules of impact energy.

The same calculation for a duck (4 hit, and an area of 2 dm²) give 88 pellet within 75 cm circle and a pheasant (5 hit and a surface area of 2.4 dm²) give 92 pellet 75 cm circle.

Note that it is fairly close to the British rule of thumb of 100 pellets in a 30 "circle.

Now these values are minimum values because the hit rate in most cases is closer to the center than the edges of 75cm circle.

How do you choose then?

And now we see that 32 grams of US6 contains about 230 pellets and with ¼ choke gives pattern with about 130 pellets. In theory, for we know now that there are many factors that affect the grade of choke. That the manufacturer of the weapon states ¼ choke should only be seen as suggestion of what we can expect. A cartridge with 32 grams of US6 is sufficient for to the pheasant / duck and the upwards given that the choke rate for the combination of weapon and cartridge is ¼ choke. With full choke we'll get about 160 pellet within 75 cm circle and it would cover everything from wild pigeon and up.

Now you do not need experiment only with the choke, but what counts is of course number of pellet within the 75cm circle, and then you can increase/decrease the amount of pellet in charge of and get the same results, or choose a different cartridge with another type of wad. 36 grams of US6 contains approximately 300 pellets, with a ¼ choke it provides, in theory, at around 160 pellets in a 75cm circle that is enough for pigeon / partridge. So the person who has a vintage gun and are looking to replace it with a modern with replaceble choke tubes, do not do it. Choose the right cartridge instead. And you should have as much chance of hitting as possible even in the shorter distances, it is better to increase pellet load and reduce choke.

From this you can choose some different types of cartridges as needed - and to test them as above - the bright person then select the ammunition that gives the most even hit the picture (even pellet distribution).

The motto is:

PATTERN ENDS LONG BEFORE PELLET ENERGY ENDS!

Since there’s no need to throw away pellets after a target if the pattern is full of holes that will make the probability uncertain even if the pattern is place as a hit over the target.  You can hit with a shotgun without hitting the bird....

For those who are considering performance at any distance - and you should keep in mind that a shotgun is fully operational out to 70-80 meter in the most extreme cases - should first look for ammunition that performs maximum regular pattern, and other hand look at striking energy.

But a standard gun with standard chokes loaded with what you get your hand on might be worthless as early as at 30 meters seen to pattern quality.

Summary

We have now seen that we can settle with 32 grams of US6 and ¼ choke for most shotgun hunting, except maybe the pure pursuit of pigeon / woodcock. In the former case, one can advantageously use US7, U.S. 7.5 or even less, for larger game you may chose much larger pellets if you want a decrease the number of pellets in the body. Are we going to compensate a little miss in the distance assessment, variations in muzzle velocity and low temperatures, we can just in case go up to 36 grams US5 at the same choke at the end of the season if they intend to shoot mostly fur game, but basically suffice to say 32gram U.S. 6 and ¼ choke.

And now we can see that the old game-keeper was not so wrong in all cases: five pellets US6 is sufficient for most of what we legally can shoot with the shotgun. Already in Victorian Britain knew this. A bit strange that this knowledge does not become more entrenched in almost 200 years.

And even if they do not shoot deer with buckshot in the UK the rule applies for deer.

So you need to test preferably 5 different brands of US6 and US5 and with different loads. And on 20 shots, we can fire five shots with each cartridge in order to get some more statistically stable data. And now we've really done everything except the actual test, we have the tool to evaluate and we minimized the number of shots we need to shoot.

And if you when testing are to discover just your own gun moves the center of the pattern when using different loads it is, if not desirable, rather normal. If it is so much that it affects the hit probability each and one of us must each determine, but a movement of one dm in some direction for each barrel will probably not be that bad. But it may be considerably more.

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Last update: 2015-05-17