Airsoft pellets

Airsoft pellets are typically made of plastic spheres, ranging in size from 5.98 and 6mm in diameter, and in weight from 0.12 to 0.43 grams. In addition to (crude oil derived) plastic, starch-based biodegradable plastic, metal or graphite coated and solid steel pellets are also available. Pellets other than 6 mm, 0.12 g, 0.20 g, or 0.25 g plastic or biodegradable pellets are not commonly used outside of Japan. Airsoft pellets are most commonly found in white and yellow, though many other colors are produced, including green, blue, orange, gold, and red.

Varieties of pellets

Glow-in-the-dark tracer pellets are can be used in conjunction with a special device that "charges" the pellets up by flashing them with a quick burst of visible light after leaving the barrel, so that they remain luminescent in flight for use during nocturnal games/operations. This tracer unit is usually disguised as a Silencer.

There have also been airsoft models that use non-spherical pellets. The best known of these is the Asahi "Blade Bullet", which are now extremely difficult to find and quite expensive to buy. These were designed to be shot from the short-lived Asahi M700 and M40 premium grade rifles, which were produced in 1993. Compatibility with other airsoft guns is highly limited, especially due to their incompatibility with hop-up features.

Paint-filled pellets are also available. Airsoft models equipped with the HOP-Up projectile stabilising system are not able to use these, as the thin shells are liable to break in the barrel, soiling it with paint. These special pellets are also incompatible with Airsoft models using mechanised feed systems, such as clockwork magazines, for the same reason.

6 mm pellet weights and their usage

0.12 g - Used by some gas and spring weapons. High velocity and low stability. Not to be used in high end AEGs such as Tokyo Marui and Classic Army
0.15 g - Same uses as 0.12 g. Uncommon. Not to be used in high end AEGs such as Tokyo Marui and Classic Army
0.20 g - Standard weight for most weapons. AEGs use these or slightly heavier pellets.
0.23 g - Heavier pellets for AEGs. Blends speed of 0.20 g with range and accuracy of 0.25 g.
0.24 g - An oddity. Only known manufacterer is Airstrike (subsidiary of Daisy) and only used in higher-power spring rifles, such as the Marksman 1950 Series (no internet documentation on that gun)
0.25 g - Heaviest weight for standard AEGs, blowback and spring guns. Tokyo Marui standard AEG, gas, and spring guns are set at the factory for 0.25 gram BB's, and they usually include a package of 200 of these with the gun.
0.28 g - For highly upgraded AEGs or sniper rifles. Significantly cheaper than 0.30 g but yields similar performance
0.29 g - Maruzen Super Grandmaster BBs, designed for their Air Precision Shooting series of guns. One of the most precisely ground and accurate BBs available, but cost more than other alternatives.
0.30 g - Standard weight for most sniper rifles. Western Arms pellets for their gas blowback pistol series. Uncommon.
0.36 g - Heavier pellets for sniper rifles. Very slow but have high stability.
0.43 g - For the highest level of upgrades in spring and gas sniper rifles. Usually graphite coated.

8 mm pellet weights and their usage

0.34 g - Low weight
0.45 g - Standard weight
0.60 g - Heaviest weight

BB quality

The quality of airsoft pellets does vary among manufacturers, as well as among various lines by the same manufacturer. Lower quality pellets tend not to be perfectly round, exhibiting pock marks, seams or nipples from the manufacturing process.

Higher quality pellets aim to be perfectly spherical. Some very high end projectiles are ground or tumbled with low-abrasive materials to provide a high sheen.

Silicon or graphite based lubricants have also been introduced into the production of some products, though lubrication tends to counteract the effectiveness of HOP-Up spin.

Pellet ballistics

Pellet velocity, energy and weight

The pellet velocity of automatic electric guns is determined in large part by the tension of their main spring and so there tends to be a stratification of values. The most common airsoft velocity limits are between 300 to 400 ft/s for AEGs and 400 to 500 ft/s for single shot guns (sniper rifles). Below are some common speeds of airsoft pellets.

3.00 g is the typical weight for a paintball pellet. At this weight a pellet flying at 90 m/s results in 12.54 J and 14.99 J for 100 m/s. This weight is for comparison purposes only and is not used on Airsoft. Higher energy but different collisions read Elastic collisions (airsoft) and Inelastic collisions (paintball) topics for further information.
Red line are the usual Crony (chronograph) weights for 6 mm 0.20 g.

Dangers to humans

Airsoft pellets typically leave small welts on human targets. While mildly painful, pellets are not especially damaging to the skin. Eye protection is universally required to prevent damage to eyes. It is also often recommended that full face masks be used during airsoft matches to protect the players' teeth and ears. On very rare occasions players have had teeth chipped or knocked out or ears injured by a pellet placed in the right location.

Although there have been no documented cases in airsoft, there is a possible hazard when dealing with graphite-coated pellets. In the early days of paintball some players would coat their rounds with graphite so that they would feed into the gun better. Players started to find that if any rounds broke the skin the wound would not properly heal, leaving a scar. Players and field owners should be aware that this problem may exist in the realm of airsoft as well.

The following excerpts are from the United Kingdom Parliament's "Principles of firearms control", Home Affairs Select Committee Second Report, 6 April 2000, expound on the level of danger involved with low-energy projectiles:

"25. The Firearms Act 1968 defines a firearm "a lethal barreled weapon of any description from which any shot, bullet or other :missile can be discharged".In this context, a "lethal weapon" means a weapon capable of firing a projectile with sufficient :force to inflict more than a trivial injury, i.e. with a force sufficient to puncture the skin.^*
"26. The Home Office and the Forensic Science Service considers that the lowest level of muzzle energy capable of inflicting a penetrating wound is one foot pound force (1.35 J): below these power levels, weapons are "incapable of penetrating even vulnerable parts of the body, such as the eye".However, more recent analysis by the Forensic Science Agency for Northern Ireland has indicated that a more reasonable assessment of the minimum muzzle energy required to inflict a penetrating wound lies between 2.2 and 3.0 ft·lbf (3 to 4 J).[55 We will deal more fully with this discrepancy at paragraphs 123 to 130 below."
"123. The power level at and above which an air weapon is considered a firearm in law is presently set at 1 ft·lbf. However, we note above that the Forensic Science Agency of Northern Ireland has more recently assessed the power level at which a barreled weapon is capable of inflicting a lethal wound as between 2.2 and 3 ft·lbf, and the Secretary of State for Northern Ireland has proposed that the law relating to firearms in Northern Ireland be amended to take this into account.^*"

On another document also regarding firearms, "The Eleventh Annual Report of the Firearms Consultative Committee", the penetration levels lies between 2 and 3 J based on a research for US Army and DiMaio's work in "Minimal Velocities Necessary for Perforation of Skin by Air Pellets and Bullets, Journal of Forensic Sciences".

Date	Reference	Energy level	Observations
April 2000	Principles of firearms control 26
	Home Office and the Forensic Science Service;	1,35J	penetrating wound (later changed by paragraph 123, see below)
April 2000	Principles of firearms control 123
~2000?	Forensic Science Agency for Northern Ireland;	3,00J~4,00J	penetrating^/lethal^ wound
March 2002	The Eleventh Annual Report of the Firearms Consultative Committee
	DiMaio's work in Minimal Velocities Necessary for Perforation of Skin by Air Pellets and Bullets,
	Journal of Forensic Sciences;	2,00J~3,00J	penetration level

Hop-up & Bernoulli's principle

Bernoulli's principle as applied to an airsoft pellet is as follows. As a spinless spherical pellet flies along its trajectory through the air (the air being the "fluid" in this case) the pressures on all sides of the pellet are equal because the air is traveling the same velocity relative to the surface of the pellet. If a spin is applied to the pellet about an axis perpendicular to the velocity vector (i.e. a backspin) the air will be rushing faster (relative to the pellet surface) on the side that is spinning away from the velocity vector and slower on the side that is spinning towards the velocity vector. Bernoulli's principle says this difference in fluid velocity implies a difference in pressures, which is a force that will cause the pellet to move in a direction perpendicular to the velocity vector.

Airsoft hop-up devices apply a backspin to the pellet so that the pressure force acts on the pellet opposite to the direction that gravity is pulling it. This causes the pellet to fall less over a given distance than it would without the spin applied to it.

In airsoft guns this is often implemented as a rubber piece at the rear of the barrel that is thicker at the top of the barrel than the bottom. As the pellet moves past this piece it tends to roll, inducing a backspin. This is usually adjustable so that the effect can be tuned to suit the weight or speed of the pellet, and each player's preference.

Another cause of the apparent lift on an airsoft pellet is the Magnus effect. There is a layer of non-moving air on the surface of the pellet (boundary layer). This is why a golf ball has dimples; this layer acts like ball bearings. With the case of a spinning ball, this layer gets thrown off at an angle. Newton's laws say that in order for air to be thrown in one direction, the ball has to move in the other direction. According to the Magnus explanation, the rotating ball would throw air downward and to the rear, thus giving lift. The air on the bottom of the ball is slowed down, so when the separated air comes back together, it is lower than the middle of the ball appearing like a comet's tail pointing down. This can be verified in wind tunnels and is very well documented in fluid dynamics physics textbooks.

External Links

http://landau1.phys.virginia.edu/classes/311/notes/aero/node2.html
http://www.mathpages.com/home/kmath258/kmath258.htm (skip the calculus and scroll down to the bottom)
http://www.rap.ucar.edu/staff/crook/magnus.html
http://wings.avkids.com/Tennis/Book/magnus-01.html

Pneumatic weapons