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:
TypeDiameter (mm) Caliber Frontal Area ( mm2 ) Frontal Area ( m2 )
Airsoft6 0.235 28.27 0.0000283
Airsoft - Large8 0.315 50.27 0.0000503
Steel BB's4.5 0.177 15.90 0.0000159
Paintball17.2 0.68 235.06 0.0002351

 

        Section I-A-02: Density / Volume and Terminal Velocity

Calculating density D as

D = M / V
Here are densities of various airgun projectiles:
TypeDiameter (mm) Mass (grams) Mass (grains) Volume ( m3 ) Density    ( kg /m3 ) Terminal Velocity
 (fps) (mph)
Airsoft6 0.121.9 0.0000001131 1061 40.0 27.3
Airsoft6 0.203.1 0.0000001131 1769 51.6 35.2
Airsoft6 0.253.9 0.0000001131 2211 57.7 39.3
Airsoft6 0.304.6 0.0000001131 2653 63.2 43.1
Airsoft6 0.365.6 0.0000001131 3184 69.2 47.2
Airsoft6 0.436.6 0.0000001131 3803 75.7 51.6
 
Airsoft - Large8 0.345.2 0.0000002680 1269 50.1 34.1
Airsoft - Large8 0.456.9 0.0000002680 1679 57.6 39.3
 
Daisy BB4.5 0.335.1 0.0000000477 6916 87.7 59.8
Copperhead BB4.5 0.365.5 0.0000000477 7545 91.6 62.4
Dynamic BB4.5 0.426.5 0.0000000477 8803 98.3 67.4
Daisy Heavy BB4.5 0.456.9 0.0000000477 10689 102.4 69.8
*Copperhead Pellet4.5 0.517.9 -- -- -- --
 

Paintball

17.2

3.2

 

0.0000026972

1201 71.4 48.7
 

* 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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