Section I-A: Physical Characteristics of Pellets
Section I-A-01: Diameter
The average diameter of a BB tends to be a little less than 6mm but for all practical purposes we’ll use a diameter of 6mm. I did separate calculations using a diameter of 5.90 mm and determined that the results were so similar that it wasn’t worth modifying -- I kept it at 6mm.
For comparison’s sake, I’ve included the diameter’s of standard BB's as well as paintballs:
|Type||Diameter (mm)||Caliber||Frontal Area ( mm2 )||Frontal Area ( m2 )|
|Airsoft - Large||8||0.315||50.27||0.0000503|
Section I-A-02: Density / Volume and Terminal Velocity
Calculating density D as
D = M / VHere are densities of various airgun projectiles:
|Type||Diameter (mm)||Mass (grams)||Mass (grains)||Volume ( m3 )||Density ( kg /m3 )||Terminal Velocity|
|Airsoft - Large||8||0.34||5.2||0.0000002680||1269||50.1||34.1|
|Airsoft - Large||8||0.45||6.9||0.0000002680||1679||57.6||39.3|
|Daisy Heavy BB||4.5||0.45||6.9||0.0000000477||10689||102.4||69.8|
* Pellets range from about 5 to 9 grains; 7.9 is by no means the weight of all pellets. Additionally, because of the non-uniform shape of pellets, it's impossible to accurately calculate volume and density (without using AutoCAD).
Notice that 8mm BB's, though heavier, are still less dense as compared to 0.20g 6mm BB's.
To give you an idea of other densities, at sea level and 15 C, air density is 1.225 kg /m3, which is nearly a thousand times less dense than even 0.12g BB's. Just for the sake of comparison, here are some other densities: fresh water (1000 kg /m3) and salt water (1027 kg /m3), which is why even 0.12g BB'swill sink in water. As an additional comparison, the density of different 0.177” bb’s ranges from 6916 to 10689 kg /m3 whereas a standard paintball has a density of 1201 kg /m3 .
It is interesting to note that the terminal velocity of 0.20g 6mm BB's is slightly over 50 fps. I have read where people state that an airsoft pellet, when fired straight upward, will land with the same velocity that it was fired at. This is erroneous thinking. After reaching the apex in its trajectory, a BB will accelerated downward until it reaches its terminal velocity. This phenomena is best illustrated in paintball. A paintball may be fired skyward at over 300 fps, but lands it such a low velocity that it often bounces off of the ground as opposed to shattering. The reason for this is that the paintball -- fired upward at 300 fps -- falls at its terminal velocity, or roughly 70 fps.
(Just for greater explanation, terminal velocity is NOT the maximum speed of a projectile, but rather the velocity of a falling object wherein the force of gravity is negated by the force of drag. Once an object in free fall reaches its terminal velocity, it will not fall any faster.).
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