Fact and Figures

Shotgun Calibres

The bore number of a shotgun (e.g. 12-bore) is derived from the reciprocal weight in pounds of a spherical ball of lead which has a diameter equivalent to that of the gun barrel. Thus a 4-bore has the same internal diameter as a ¼-lb ball of lead and a 20-bore barrel will allow a ball of lead weighing 1/20-lb to pass along it. The calibres most commonly found in Britain are the four, eight and ten bores (used principally for wildfowling) and the more common twelve, sixteen, twenty and twentyeight bores.

Choke

The question of choke is one that is often misunderstood. By the term choke, we mean the amount of constriction towards the muzzle end of a shotgun barrel which the gunmaker has incorporated to reduce the spread of pellets. Although other factors such as cartridge construction can also affect spread, the following table gives the theoretical effect of various degrees of choke;

Contrary to popular belief, the spread of pellets is not significantly affected by the calibre of the gun. The spread from a half-choke 12-bore will be the same as from a half-choke 20-bore. The only difference is that a lighter cartridge load will place fewer pellets in the pattern.

British Shot Sizes

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