Ammo GGDT calculations

[jared555]

Is there a guide somewhere with what to put in for the Friction parameter in GGDT for say, a marble? (A list of different common ammo could be of benefit

[skyjive]

I don't think its tremendously important, I always leave it at the default 0.5 psi, for most situations I think the propelling force is far greater than any frictional forces.

[MrCrowley]

It probably only matters for super long barrels (like 30'+) anyway.

[kenbo0422]

I don't know where I got this, but:

Drag Coefficients for Projectiles

Sphere (smooth) 0.07 – 0.1
Sphere (rough) 0.4 - 0.47
Bullet shape (Round Nosed, Flat Back) 0.295
Boat-tail Bullet (Pointed Nose, Part tapered back) 0.271
Half Sphere 0.42
Cone 0.50
Short Cylinder (square side profile) 1.15
Long Cylinder (rectangular side profile) 0.82
Streamlined body (teardrop) 0.04


They seem to work very well in the GGDT formulas.

[Ragnarok]

@kenbo0422: Those are for aerodynamic drag (i.e. air resistance), NOT contact friction.

[kenbo0422]

Oops... I misread the question....

[jimmy101]

Is there a guide somewhere with what to put in for the Friction parameter in GGDT for say, a marble? (A list of different common ammo could be of benefit

Measure it.

Does the marble roll through the barrel on it's own? Then the friction is essentially zero.

Do you have to push the marble with a stick? Use a scale to measure the required force and convert it to the proper units for GGDT.