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Topics - gvp

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1
An excel implementation of the following article.
https://www.sciencedirect.com/science/article/pii/S2214914717301459

See attached excel file.

Happy shooting ...

2
Ballistics / Shotgun Ballistic Calculator
« on: December 21, 2020, 01:15:46 AM »
I've made a very simple excel file in order to calculate Velocity, Energy and TOF for shotgun BB's.
1. What is the BB's ballistic coefficient ? Can it be calculated ?
2. Any idea how to make this simple excel file more reliable according to atmospheric conditions and the subsonic, transonic and supersonic region ?

Thank you in advance,
Bill

3
BC=Ballistic coefficient
Cd=Zero-yaw drag coefficient
M=projectile mass
D=Projectile diameter (caliber)
P=air pressure
T=air temperature
H=air humidity
shape=Geometric shape (form) of the projectile
u=projectile velocity
us=sound velocity at the projectile's atmosphere
u/us=projectile velocity/sound velocity ratio
SD=Projectile sectional density
i=form factor


Are the following points true or false ? (with the approximations used in BfX)

- us(P, dair)

- dair(P,T,H)     =>     us(P,T,H)

- BC(M, D, shape, u, P, T, H) or BC(M, D, shape, u/us)

- Cd(shape, u, P, T, H) or Cd(shape, u/us)

- SD=M/D2

- BC(M, D, shape, u/us)=SD/i(shape, u/us)

- i(shape, u/us)=Cdprojectile(shape, u/us)/Cdstandard projectile(u/us)

- Standard Gx projectiles always have diameter 1" and mass 1 lb

- A projectile with the exact same shape with the standard projectile (of the Gx drag function), but with different dimensions and weight, has a BC=SD at the same drag function, at all velocities

- Two projectiles with the same shape but with different dimensions and weights have the same Cd in the same velocity and at the same atmosphere.

- Lets say that we have a projectile with unknown BC ... the right way to build the BfX model for it is:
1. Compare the shape of the projectile with the Gx shapes and select the one more close to it.
2. Measure the BC near the muzzle (higher velocity with e.g. velocity differences at 2 points) according to Gx drag model selected in step 1.
3. Build the BfX model with the BC measured in step 2 and the drag function selected in step 1.


- Last question: why the BfX custom drag functions need as an input the length of the projectile ?

4
General discussion / Small difference in moa calc
« on: May 28, 2013, 03:44:35 PM »
Dear admin,
what formula do you use for length to angle conversion?

In the attached file you will see a difference between drop (in moa) in a distance of 500m with your formula and the cosines law ...

Thank you,
Bill

5
General discussion / Book of Arthur Pejsa used ...
« on: May 19, 2013, 01:41:45 AM »
@admin
Which book did you used for BfX ?

Modern Practical Ballistics by Arthur J. Pejsa ?

6
Member projects / FT reticle point of impact
« on: April 30, 2013, 10:26:57 PM »
Not tested in real world yet ...


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