Airsoft Sniper Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
39 Posts
Discussion Starter · #1 ·
Does anybody know how to calculate an fps from one using another at a heavier grade?

For example:

386fps using 0.36g bb's equates to '___' if using 0.2g bb's.

I used to have the formula but have mislaid it ( ::) ).

The above example is actually 386 on .36g = 518fps on .2g. I know this as my vsr was running that once.

Cheers.
 

·
Registered
Joined
·
39 Posts
Discussion Starter · #3 ·
Thats all well and good, But I need to work out from the current fps a specific wieght is fired at now, what would be in fps if I changed the weight.

i.e .36 @386fps, what would that fps equate to on a .2??
 

·
Registered
Joined
·
268 Posts
If you scrolled down, you would probably have seen it.

386 fps with a .36 = 516.53 witha .20

You take the joule from the first calc. and put it in the 2nd calc. with a different weight and you get m/s, fps, effective range in feet and meters.

Hope this answered your question.
 

·
Premium Member
Joined
·
716 Posts
Physics lesson of the day:

First, you need to know the mass and velocity of a test base of BBs.

For example, you're given .2g BBs and you know that they're shooting at 400 FPS. You then need to convert FPS to m/s, using the conversion factor, which is 3.28. You can then use those numbers to solve for energy, in Joules.

So first, 400 FPS / 3.28 = 121.95 m/s

Now you know the mass and velocity, so you can use the formula for energy, which is:

Energy = 1/2 x Mass x Velocity^2

In the case of my example it would be 1/2 x .2g x 121.95^2 = 1487.21 J

From there, you can then calculate the velocity of any weight BB you desire, using the following equation:

Velocity = (√2xEnergy/Mass)

In this case, you could do:

(√2 x 1487.2 J /.36 g) = 90.90 m/s

Now, you simply just need to use the conversion factor for m/s to FPS, which again is 3.28

So, 90.90 m/s x 3.28 = 298 FPS

For those of you that don't use the silly imperial system, you can drop off two steps from this equation, since you already should have the Vi (velocity initial) in m/s and are solving for Vf (velocity final) in m/s.
 

·
Premium Member
Joined
·
716 Posts
Not many people like the physical sciences, too much math. I actually am good at math, but really dislike it. For some reason, chemistry and physics, I actually enjoy the math side of things.

The nice thing about chemistry is you may forget it fairly easily...I had about 1.5 between my high school chemistry class and my first college chemistry class and couldn't remember a thing. But within 1-2 examples, I could remember exactly how to do all of the equations.
 
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top