Airsoft, like any other sport, involves many scientific principles that go relatively unnoticed. In the heat of battle, one would rarely worry about something like transferring kinetic energy. While knowing airsoft physics won’t realistically help you in the game, it’s good to know the principles. On the other hand, knowing granular projectiles can help you in your game.
The pellets transmit very small amounts of kinetic energy mainly because of their size. Energy transfer is basically impact force. Airsoft and Paintball’s energy transfers have been compared, and Paintball transmits exponentially more energy. Energy transfers are measured in joules, which is the SI derived unit of energy. A standard 20g BB travels at 300 ft/sec. 8 joules, while a standard paintball travels at the same speed approximately 12 joules. Energy transfer can actually be calculated using a mathematical formula; E = 1/2mv2, where E equals joules, m is mass in kilograms, and v is velocity in meters per second. Since paintballs transmit more kinetic energy, they can be considered more harmful than airsoft pellets.
The weight of airsoft pellets greatly affects their speed and trajectory. The lighter the grain, the faster it will travel, but it will also be less fine due to the fact that it will be more susceptible to environmental factors such as wind. Heavier pellets have straighter trajectories, so they are favorable to lighter pellets, but in many cases heavier pellets cannot be used because the airsoft gun using them is not powerful enough to propel the pellets at a rapid rate. Therefore, players who want to use pellets heavier than 0.25 grams need to upgrade their rifle. Another benefit of heavy pellets is that they decelerate slowly, unlike light pellets, which start quickly but quickly lose speed. An Airsoft sniper typically uses .30g pellets because of their higher stability, but sniper weights can go as low as .43g (although expensive upgrades are needed to use this pellet grade). The heaviest pellet is 0.88 g, which is never used in airsoft because it is incredibly slow, not to mention very dangerous, since it is usually made of steel.
The velocity of the pellet is primarily determined by the tension of the spring used to propel the pellet, or, in the case of gas airsoft guns, the type of gas used. The energy transfer is proportional to the velocity of the pellet, and the velocity is also strongly affected by the weight. For example, a .12g pellet using .800J (common energy rating in airsoft) energy will initially transmit 375 fps. However, a 20-gram pellet using the same amount of energy will only travel about 280 fps, and a 0.45-gram pellet will travel at about 200 fps. For a .45 gram pellet to reach a velocity of 375 fps from a .12 gram pellet, it would need to use more than 2.50 joules of energy.
Bernoulli’s principle is the way pellets fly. It is also interesting that this is the principle by which planes reach lift. Bernoulli’s principle states that fluid velocities increase with decreasing pressure. For airsoft, there is a liquid (air) above the pellet at a relatively high velocity, which means that the pressure above the airsoft pellet is lower than the pressure below it, as there is less air flowing under the pellet as there is above it. Therefore, the pressure under the pneumatic pellet will push the pellet up and lift it up, allowing it to fly for a long period of time. The jump systems in airsoft guns apply backspin to the pellets, which makes air travel faster along the top of the pellet and creates a larger pressure difference between the top and bottom.