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 Post subject: How do you convert FPS between .20g and .25g BB's?
PostPosted: Thu Feb 05, 2009 12:00 am 
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If you ever wanted to convert an FPS reading using .20g BB's and figure out what your FPS is using .25g BB's, or any weight of BB here's a handy online utility: ... s_calc.htm

And if you want to know more about how these numbers are calculated, read on...

Snake wrote:
This is a simple essay on how using joules could be more useful than using “fps” and how exactly to use joules.

Now for the juicy stuff. A joule is a unit of energy. In other words, a joule equals one-half times the mass times the square of the velocity. Joules are static; they do not change. 10 different projectiles fired from the same gun will all hit a target with roughly the same amount of energy. For example, a .12 gram bb flying at 450fps and a .25 gram bb flying at 302fps will impact with the same amount of energy (1.14 joules). The fps of a gun may change due to bb weight. The joules will not.

Thus, by using joules as our standard term for power…people will know exactly what you mean. No more “Were you using .25g bbs or .20g bbs?” questions.

But that’s just the use of joules in theory. I’m sure most of you are wondering, “How the heck am I supposed to find out how many joules my bbs impact with?” If you have a chronograph, it’s extremely simple using the equation for joules (this should be easy for those of you who have taken physics).

1. Convert your feet per second to meters per second. This is your velocity.
-(fps x 12) / 39 = mps
2. Convert your bb weight from grams to kilograms. This is your mass.
-Divide your bb weight by 1000.
3. Plug your velocity (v) and mass (m) into this equation. E equals energy or joules:

E = .5m(v^2)

Here is an example:
-Say you have an AEG firing 380fps with .2 gram bbs.
-380fps = 117mps
-.2grams = .0002 kilograms

-E = .5 x .0002 (117^2)
-E = .0001 (117^2)
-E = .0001 (13689)
-E = 1.3689
-Joules = 1.37

That concludes this tutorial. Remember, you should be careful when firing higher than 1.5 joules in an AEG or GBB and never skirmish with any weapon shooting harder than 2 joules. Sniper rifles may vary, but very strict ROEs must be followed.

If this post leaves any holes, results in a deep thought, or springs any more questions, feel free to drop me a pm or add them here.

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