Every pellet counts!

In order for a shotgun shooter to control the amount of spread for a given cartridge/load, some form of restriction to the parallel bore is needed. The trouble is, it is not as simple as that, and the correct choke choice is as hot a topic as the best calibre is to rifle shooters!

The options

You can have either a fixed or multi-choke system and both have their own pros and cons. Because of this, there are lots of aftermarket, specialised choke tubes.
As the pellets in the shot column pass down the barrel, a small amount of restriction at the muzzle ‘squeezes’ this column, tightening it as it exits. Obviously, the amount of restriction the chosen choke provides affects the rate that the pellets spread out.
Of course, open and tight chokes have their own specific uses. Skeet shooters need as open a choke as possible for a wide spread, as do walked-up woodcock shooters in dense woodland. Most people are happy with the mid-range chokes for rough or game shooting, whilst wildfowlers like a tighter choke to increase their effective range.
Typically, you have a range of increasing restrictions on the original bore diameter, and these include Cylinder, Skeet, ¼, ½, ¾, and Full. However, you can also have all manner in-between, so 3/8th, 5/8th, and Extra Full. You can also choose between recessed chokes or extended chokes.
See the ‘Specifications Table’ for a guide to the common chokes. Note that the diameters for chokes vary dependent on the bore used.

Fancy chokes

Some firms have made a living out of custom-made choke tubes, notably Teague and Briley. Teague chokes are made in the UK, and they offer not only a comprehensive range of specialised chokes but also a re-choking and fitment service. Here, you can specify the exact size, length, and internal tapers that you require. Options include specialized clay or game chokes that can be specified as extended or flush fit, depending on your type of gun and/or preference. You can also have ported chokes that help to eliminate muzzle flip and to reduce recoil.
Steel shot must not be used in chokes more than ½ (Modified). This is due to the extra hardness of the shot, which could cause damage. You can improve patterns with an extended 1/2 choke if you like, and many wildfowl guns come with extended steel chokes.
Different manufacturers use different chokes and will often alter the spec. For example, Browning’s Invector choke is not the same as their Invector Plus, which is longer. Also, Mossberg uses an Invector-type choke, so you can use this on some models, i.e. their pump-action, where this popular style of choke tube means you can choose from a wide range of aftermarket options. I was able to attach an A-TEC A12 sound moderator via a modified, extended Invector tube.
I prefer flush-fit chokes myself, as they look better. However, the extended chokes are very popular amongst wildfowlers using heavy loads and steel. Also, clay shooters can appreciate the longer and gentler taper of an extended choke as the design really helps smooth the transition from barrel to choke to produce a more uniform and denser pattern with fewer holes in it. This helps minimise the chance of a clay pigeon slipping through.
Also, some calibres, like .410, can be very choke-specific/sensitive, as they have a small diameter to start with. This means any choke restriction can be detrimental because it may cause the pellets within the shot column to squash together and deform, leading to a poor pattern down range.
Calculations
Chokes are specifically designed to help achieve the best pattern possible from the chosen load. Interestingly, if you know the shot size and the weight, then you can calculate what percentage of the pellets will appear in a 30” circle at 30 yards, by using a simple formula.
There is, of course, no substitute for actually shooting a load in your shotgun, but it will give you some idea of what to expect from a new load. I use Lyalvale Express pattern boards for all the Gun Mart shotgun tests.

Using tables A and B, you can calculate the number of pellets that will land within a 30” circle at the ranges indicated. For instance, if you are shooting a 12-gauge, 1oz/28.5-gram load of No. 7 pellets through a ¾ choke at 40 yards, you first need to find out how many pellets there are. Looking at Table A, you will see it is 340. Next, look at Table B to find the percentage, which is 65. Finally, multiply 340 x 65 and then divide it by 100. This will give you the total number of pellets to hit within 30” at 30 yards – 221.
If you decide to shoot that load at 25 yards, then 100% of the payload (340 pellets) will hit the 30” target area. At 50 yards, only 46% will hit, which means 156 pellets.
So, you can see by altering the choke, shot weight, and pellet size, you can get a good indication of how dense your pattern will be and various distances. It is also worth noting that this density, not spread, can be altered by different pellet types i.e., coated copper or nickel.
If you don’t have the exact pellet weight shown on the chart, then this table shows the number of pellets per 10-grams for each pellet size, so you can add, subtract, or divide the figure to achieve your shot charge of a specific pellet size.

Conclusion

Trying out different chokes, just like trying out different rifle loads, can quickly have you tearing your hair out. I use various chokes for tests all the time and I still get surprised. Sometimes, it is better to learn the right amount of lead and the correct swing before getting involved with different chokes, otherwise, you will be wondering if you missed because of the choke and not the other way around. The choke is only one part of the firing sequence, and chamber length, forcing cone length, as well as back boring, make a massive difference to the effectiveness of chokes on patterns down range.
One thing I would certainly recommend is to buy some pattern boards and shoot your shotgun and load with the chokes you have to see what results you get.