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Ammo GGDT calculations
Posted: Fri Jan 02, 2009 12:05 am
by 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
Posted: Fri Jan 02, 2009 12:24 am
by 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.
Posted: Fri Jan 02, 2009 12:56 am
by MrCrowley
It probably only matters for super long barrels (like 30'+) anyway.
Posted: Wed Oct 14, 2009 11:06 am
by 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.
Posted: Wed Oct 14, 2009 11:16 am
by Ragnarok
@kenbo0422: Those are for aerodynamic drag (i.e. air resistance), NOT contact friction.
Posted: Wed Oct 14, 2009 11:30 am
by kenbo0422
Oops... I misread the question....
Re: Ammo GGDT calculations
Posted: Wed Oct 14, 2009 2:04 pm
by jimmy101
jared555 wrote: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.