Ok, so I took a new container of airsoft pellets and calculated the volume that the bb's filled, I did this by using an overflow container... You fill the container with water, until it overflows. You wait for it to stop overflowing, and then you put the object in the water and collect what overflows. I do not have any tools for measuring volume, as in graduated cylinders or flasks, so I have to do this the hard way.
I took all the water I collected and placed it on a postal scale (yes, I zeroed out the scale with just the container on it). It weighed 2 lbs 1 oz, which I have calculated to be 2.0625lbs. I know that one gallon of water weighs approx 8.35lbs, so I took the weight of my water and divided it by 8.35.
2.0625/8.35=.247005988 That is how many gallons of water I collected, hence the approx. space, in gallons, that 5000bb's takes up. We know that 1 gallon is 231 cubic inches, and 1 cubic foot is 1728 cubic inches, so there are 7.48051948 gallons in a cubic foot. Once we divide that number by the number of gallons that 5000bb's takes up, we can figure out how many bb's in one cubic foot.
7.48051948/.247005988=30.2847698 That is how many 5000s of bb's we can fit in a cubic foot. Knowing that 5000bb's has a surface area of 6.08160938 square feet, we can figure how many sq ft per cubic foot of bb's.
30.2847698*6.08160938=about 184.2 square feet per cubic foot.
Through all of this, I have come to the conclusion that, 1 cubic foot of 6mm Airsoft BB's has roughly 184.2 square feet of surface area.
This means that they have more surface area than bioballs (which clock in a 160in^2/feet^3), but are probably more expensive.
Looking at prices online, it is about $15 for 5000 pellets. So, it would cost about $450 for a cubic foot of these, ouch.