On this page I hope to explain to the beginner some of the mysteries surrounding barrel diameters, choking and shot sizes. Aimed mainly at the beginner to shooting in general and wildfowling in particular, this page may also assist the more experienced. Hopefully this page will help make sure you have the right combination of barrel, choke and shot suitable for the quarry, "Horses for courses" is the key phrase. Many myths surround the choice of choke, barrel length and best shot size. The onus is on the shooter to choose a combination which will give them the best chance to despatch the chosen quarry humanely. The information below is only a guide line and the make of cartridge and type of gun plus the shooters own ability will all influence the "best" combination for each individual.

Barrel diameter

The most commonly used shotguns for wildfowling in the UK are 4, 8, 10 and 12 bore although 4 bores are not used extensively now. The bore of the shotgun barrel is defined by the weight of a single ball of lead having the same diameter as that of the internal measurement of the barrel. One pound (16 ounces) is divided by the weight of the ball to determine the bore, eg If a ball weighing 1/8th of pound (2 ounces) and measuring the approximate diameter of the barrel would pass through it the barrel would be classed as an 8 bore (16 divided by 2). There are the odd exceptions to this method of determining the bore or calibre of a weapon the four ten is the classic example it's name is derived from it's barrel diameter which is 0.410 inches. The British gunmaking industry usually use as standard the following bore diameters in inches:-

Bore Size 8 10 12 16 20 28
Bore Diameter 0.835 0.775 0.729 0.662 0.615 0.550


The choke is basically a measured degree of constriction at the business end of the shotgun which "chokes" the spread of the pellets thus reducing the diameter of the pellet pattern. Shotguns may be "fixed" choke which is one particular degree of choke "Multi - choke" which are interchangeable choke tubes screwing into the end of the muzzle or possibly "Poly-chokes" which increase or decrease the degree of choke by turning a device attached to the muzzle end of the shotgun. The degree of choke ranges from true cylinder which is the most open to full choke which is the tightest, other countries do use different measurements in some cases or different descriptions for a similar choke for example the American gunmakers refer to the equivalent of UK half choke as "modified" but choke sizes commonly used by British gunsmiths are measured in thousands of an inch as shown below.

Choke type Degree of Choke Approx spread at 40 yards
Cylinder none 59"
Improved Cylinder 5 thou 52"
1/4 Choke 10 thou 49"
1/2 Choke 20 thou 46"
3/4 Choke 30 thou 43"
Full Choke 40 thou 41"

Shot sizes

Shot sizes for individual quarry are usually recommended based on experience and personal preference in most cases but the main criteria is to place enough pellets in the pattern with enough striking energy to kill the chosen quarry humanely. Pellet striking energy lessens the further away from the muzzle it gets as it's velocity decreases and the pattern produced spreads wider the chances of killing the quarry humanely are reduced considerably, It's no good hitting your quarry with a feather and expecting to kill it. This is where you must consider pellet size and striking energy in your choice of cartridges.

British shot sizes are usually given as a number although some of the larger shot used in wildfowling is "lettered" such as AAA and BB. The sizes and number of pellets per ounce used in the UK are given below, the smaller the number the larger the shot. The exceptions to this rule are for the lettered shot sizes which are reserved for the larger shot :-

AAA 0.20" 35
BB 0.16" 70
1 0.14" 100
3 0.12" 140
4 0.11" 170
5 0.105" 220
6 0.10" 270
7 0.095" 340

Most cartridge weights are shown on the box in either ounces or grams. The table below shows the equivalent weights in grams and ounces.

9 5/16 28 1. 0
11 3/8 30 1. 1/16
18 5/8 32 1. 1/8
21 3/4 34 1. 3/16
23 13/16 36 1.1/4
24 7/8 42 1. 1/2
25 7/8 50 1. 3/4


You may by now be thinking "great all I need to do is get a true cylinder shotgun and cartridges loaded with number 7 shot and I can shoot anything" If you are you couldn't be more wrong! The choice of choke, cartridge and shot size is dependant on a variety of things, the quarry, chamber length of the gun, the shooters ability and the pattern produced by the cartridge and gun combination all have a bearing on what is considered "suitable"

The recommended shot size for different quarry species used in 12 bore shotguns are shown below, these produce enough striking energy and sufficient pellets in the 30" circle to maximise your chances of a humane kill if placed on the quarry correctly. Larger shot sizes can be used in the longer chambered guns for wildfowling. Please note the figures below are to be used as a guideline, opinions may vary depending on the individual shooter but those below should do the job.

GOOSE No 3, No 1 35 to 50 yards 3/4 to Full 1.1/4 to 2
DUCK No 4 or No 5 25 to 40 yards 1/2 to 3/4 1.1/8 to 1.5/8
PHEASANT No 5 or No 6 25 to 40 yards 1/4 to 3/4 1 to 1.1/8
PARTRIDGE No 6 or No 7 25 to 35 yards 1/4 to 1/2 1 to 1.1/8
GROUSE No 7 20 to 35 yards 1/4 to 1/2 1 to 1.1/8
SNIPE No 7 or No 8 20 to 35 yards Cylinder to 1/4 1 to 1.1/8
HARE No 4 or No 5 25 to 35 yards 1/2 to 3/4 1.1/8 to 1.1/4
RABBIT No 5 or No 6 25 to 35 yards 3/4 to Full 1 to 1.1/8
PIGEON No 6 or No 7 20 to 35 yards 1/4 to 3/4 1 to 1.1/8
WOODCOCK No 7 20 to 35 yards 1/4 to 1/2 1 to 1.1/8

Ask yourself are you confident of killing your quarry humanely and consistently at the given distance? It is a fact that most live quarry is shot between 25 and 35 yards by the average shooter.


Theoretically the more pellets you can get in your pattern and on the quarry the more chance you have of a clean and humane kill. The "pattern" is judged by the number of pellets striking within a 30" circle at 40 yards and as the shot spreads this number is reduced considerably. Pattern your chosen cartridges with the gun you intend to use, you will be surprised at the resulting patterns with different cartridges through the same gun. Patterning can be done using a variety of materials, use a 30 inch circle and take note of the number of pellets within the circle. Are there any large gaps? the pattern needs to place sufficient pellets in the "killing zone" of your quarry to be effective. Too many gaps = injured birds. Find the cartridge for your gun which consistently gives the best patterns and stick with it you will find it increases your chances of shooting your quarry humanely each time you pull the trigger.

The "Chamber" is the place on the shotgun where the cartridge is inserted and can vary in length on 12 bore shotguns from 2" to 3.1/2" the standard today is usually 2.3/4" (70mm) or 3" (76mm) and more recently 3.1/2" especially for wildfowling. The cartridge you use must be suitable for the chamber of your gun or the result could be dangerous, never use a cartridge which is longer than the chamber of your shotgun, however you can use the same bore cartridges in smaller lengths. Your choice of gun and choke will depend on your chosen branch of the sport. Do you want to go wildfowling exclusively? Do you want to shoot pigeons, rabbits and game? or do you want an "all round" weapon which will allow you to do all? Think about it before you decide which shotgun is the most suitable for you.

So you've decided to choose a 12 bore for all round use. Your gun has the 3.1/2" chamber, what shot size and length of cartridges will you need? The shot size will depend mainly on two factors firstly the quarry and secondly the distance. The maximum "killing range" of a standard 12 bore shotgun is generally accepted as approximately 45 yards this can be increased to around 60 yards for the right combination of choke and shot in a 3.1/2" chambered gun. Choose your cartridges wisely and you increase your chances of success. Ask a more experienced shooter for help if you can't decide, most shooters will be only too willing to recommend the best shot size and cartridge for the quarry.

More detailed information regarding shotgun ammunition and ballistics is available from the website of Mr Jonathan Spencer Forensic Scientist and consultant at the following address. I would like to thank Jonathan for his kind permission to link to his website.