21g cartridges – do they really punch above their weight?

Q: I asked my local gunshop recently about budget cartridges and was told 21g cartridges ‘punched above their weight’, were competitively priced and would break clays virtually as far as 28g. I’m keen to save money and to know if this is true.

A: Richard says: This involves another of those interesting facts about cartridge ballistics. The simple answer is, yes, all other things being equal (shot quality and velocity in particular) that in any given gauge a smaller shot load weight can – and usually will – shoot ‘above its weight’. This boxing analogy means they will hit harder than you might think for the reduction in shot weight. (Read more on cartridges for clays here.)

This is the result of the lower sectional density of the lighter shot load, which results in reduced pellet distortion from crushing in the initial acceleration up the barrel. The shot charge in the 21g load is 25% less than the standard 28g load and the height of the pellets in the cartridge is therefore proportionately shorter. This reduces the crushing to the lower levels of pellets in the charge significantly. The more truly round pellets disperse less quickly than pellets deformed by acceleration crushing. This results in a higher percentage of the pellets remaining inside the usable pattern at any given distance, when compared with an otherwise identical but heavier shot load.

The 21g cartridges may well achieve 70% of pellets in a 40-yard pattern, whereas the 28g cartridge might achieve closer to 60% when both are fired through the same choke. To the extent that the 21g cartridges beat the 28g pattern density percentage by 10% (sometimes a little more), then the lighter shot load can be shown to perform ‘above its weight’. It is why, for a good proportion of club Sporting layouts, 21g cartridges can handle a high proportion of targets quite well. However, the 60% pattern density with 25% more pellets in the heavier charge will still produce a more dense pattern and this will handle targets at a few yards greater range. All else being equal, the lightweight will put up a good performance but the heavier cartridge will ‘win’.