GTA

All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: RICHARD59 on September 05, 2015, 01:44:03 AM

Title: chronograph
Post by: RICHARD59 on September 05, 2015, 01:44:03 AM

Hello all: I bought a chronograph and need help. Will someone explain this for me how to figure the fpe I am getting out of the fps and weight of ammo. I know their must be a mathematical formula. thank you!

Title: Re: chronograph
Post by: Smoketown on September 05, 2015, 01:57:07 AM

Chair Gun will do it for you.  Free at - http://www.hawkeoptics.com/chairgun.html (http://www.hawkeoptics.com/chairgun.html)
Just enter the values.

Or,

http://www.gatewaytoairguns.org/GTA/index.php?topic=10880.msg91915#msg91915 (http://www.gatewaytoairguns.org/GTA/index.php?topic=10880.msg91915#msg91915)

Cheers,
Smoketown

Title: Re: chronograph
Post by: Bill G on September 05, 2015, 10:13:22 AM

For the sake of having the math on hand, I'll give you the problem

KE=1/2mass*velocity squared

KE= kinetic energy
mass= pellet weight
velocity = reading from the chrony

There is some conversion that has to occur.  pellet/ boolet weight in grains has to be converted to lbs and the method I dwill describe will do this for you.

pellet weight * velocity^2/( 7000 * 32.3 * 2)

25.4 * 900^2 / (7000 * 32.2 * 2)
20574000 / 450800
45.64

7000= 1lb in grains
32.3= gravity
2= the 1/2 in (KE=1/2 M*V^2)

Hope that helps.

Bill

Title: Re: chronograph
Post by: Ribbonstone on September 05, 2015, 10:25:21 AM

Going to break it down even simpler.

velocity (in feet per second) X itself

divide that result by 450240

multiply that result by the pellet weight in grains.


So lets say 827fps with an 18grain pellet:

827 x 827 = 683929

683929 divided by 450240 =1.519032

1.519032 x 18 = 27.342576 (foot pounds)

Title: Re: chronograph
Post by: Gerard on September 05, 2015, 02:02:01 PM

I do the calculation as above manually sometimes, but this online calculator makes it very easy:
http://www.airgunsofarizona.com/energycalc.htm (http://www.airgunsofarizona.com/energycalc.htm)

Title: Re: chronograph
Post by: RICHARD59 on September 09, 2015, 12:08:51 AM

Thanks Guys