A reader asks Airgun Guru a question about pellet power
Q: Which is the most powerful pellet?
GURU SAYS: I’m afraid there’s no straight answer to the question, because power is a measure of the rate at which work is done, which will vary according to what the pellet’s energy is performing work on when it reaches the target.
If you’re asking which pellet realises the highest muzzle energy, that’s another matter, and it varies first according to whether it is shot through a PCP or a spring rifle, in addition to which, it also varies according to which spring rifle it is shot through.
In PCPs, as a general rule, heavy pellets tend to gain the most energy from the compressed air as they travel up the barrel, so they tend to give higher muzzle energy. In spring rifles, lighter pellets tend to gain the most energy from the compressed air, and give higher muzzle energy, though as already stated, that will vary hugely according to the individual rifle.
Actually, in spring rifles, the picture is more complicated than that. Pellets with thin skirts seal earlier in the compression stroke and start to move earlier, so you are most likely to find that a lightweight, thin skirt pellet will give the highest muzzle energy.
Another aspect of this question is the pellet’s ability to retain energy, because pellets slow down, and so lose energy, at different rates, depending on how aerodynamic they are. The pellet that gives the highest muzzle energy, PCP or spring rifle, is not necessarily the one that will arrive at the target with the highest energy, and the measure that airgun enthusiasts use of the pellet’s ability to retain energy is called the ‘ballistic coefficient’, often abbreviated to ‘BC’.
The BC is a decimal, usually between 0.10 and 0.028, and the higher the number, the better the pellet is at retaining energy in flight. You can find the BC values for most pellets on the Internet.
The final aspect of the question is what the pellet does with its remaining energy in the target. Pellets with very high BC reach the target with more energy, but the shape that allows them to pass through the air also allows them to pass through the target, and they can emerge from the other side of, say a rabbit’s head, without imparting all their energy. Pellets with low BC arrive at the target with less energy, but give more of their energy to the target.
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