BB Weight

OK, since there are hundreds of posts about which BB weight is the best to use, and how will BB weight affect your range and accuracy, etc, I thought I would put an answer to these in the FAQ section to try and save on people making so many posts about it.

What You Already Know

You will know that more weight = greater accuracy
and that more weight also = lower fps, however
lower fps coupled with heavier ammo does NOT = less range. In fact, up to a certain point it means MORE range, as we shall see when explained with some basic physics:


Why More Weight only means less range circa .36

The weight of the BB and the subsequent reduction in fps does not affect your range until you start getting over .36g (you will start noticing quite a lot with .43g)

The heavier the bb you use, the more steady it will be, and the more velocity it will retain in flight, so the greater the distance you will get, as well as accuracy. The only sacrifice you make is the initial FPS- which only affects the time it will take to reach the target. Of course, this only works up to a certain point. But to explain in terms of physics:

Ek = 1/2mv^2

(kinetic energy is equal to half times mass times initial velocity squared)

And we can presume that for every 0.05g added, you will see a reduction in muzzle velocity of around 35, and we take the velocity of our hypothetical rifle to be 500fps with a .2g bb, we see that:

Ek = 1/2mv^2

Ek = 1/2 x 0.2 x 500fps^2

Ek = 2.5kJ


Ek = 1/2 x 0.36 x 388^2

Ek = 2.709792kJ

Therefore with a higher mass bb, we see an increase in overall power, and therefore distance, and we know that more weight = more accuracy, it's win win.

Until we get to .43, where it drops, as we see with:

Ek = 1/2 x 0.43 x 339^2

Ek = 2.4708015kJ

So the trend shows that up to a certain point, the heavier the bb you use, the more overall power, and therefore range you will get, as well as accuracy.

Of course, since the actual calculations rely on metres per second instead of feet per second, the readings are innacurate (a 500fps rifle is more lik 1.8kJ, not 2.5 as stated above) but still show the actual trend, and I have only used fps so you can understand what I'm talking about, because if I start throwing in figures for metres per second, it'll most likely cause confusion.


What This Means For You

Well, to see how this applies to you, simply substitute in the values for your own rifle to the original equation:

Ek = 1/2mv^2

and then substitute the values in for different weight BBs, so you can see at what point your gun's range maxes out, and starts reducing in resultant energy. You can then make a decision on which weight BB is right for you.

For example, if your gun is firing below 500fps, you will see a drop in velocity sooner than .43g, probably at around .36, so may choose to use .32 or .30


Hope this post helped to resolve your questions about BB weight.

Jim

Also, I just found this website through searching on google. It is very useful, HOWEVER, their calculation for effective range is inaccurate because it does not factor in TOO MUCH hop up- i would suggest that if your trajectory exceeds 5 degrees to the horizontal, to reduce your hop-up because the effective range reading you get is incorrect (according to their graph, increase in hop up is proportional to increase in effective range EXPONENTIALLY, which is totally false)

http://www.radiant8.com/airsofttrajectory/

Jim

NICE !!!!

Great Post !!!!

Hmm , I have heard about this , and while many have tried to explain none have done it as well as you have . I think that I understand the drop in fps but not in range . I'm still gonna stick with my .28s and .25s though .

This really is helpful, but how Do I know how much my gun will drop in FPS? Because the gun I would use this for is chronoed at 400 fps with .2s, but where I bought it didn't say its FPS with .25 or 3.6

Great guide, I'm glad you posted hard facts. Now we just need to spread the word alot more!

Gracie: Ek = 1/2(.25)(400)^2


sticks

Gracie wrote:

This really is helpful, but how Do I know how much my gun will drop in FPS? Because the gun I would use this for is chronoed at 400 fps with .2s, but where I bought it didn't say its FPS with .25 or 3.6

Why does the FPS matter???

Thanks for the good info & links.

TheJim: as to your question, have you ever played dodgeball?
The faster your BB's are flying the better!
As long as your within limits for the field you play in of course.
(I would never THINK of playing with an extremely high FPS gun, with a bunch of guys with their guns tuned similarly in the woods...)

I use black BB's as people don't see them coming .25g is the lightest I use for my KWA KM4A1