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Ammo GGDT calculations

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Ammo GGDT calculations

Unread postAuthor: jared555 » Fri Jan 02, 2009 12:05 am

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
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Unread postAuthor: skyjive » Fri Jan 02, 2009 12:24 am

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.
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Unread postAuthor: MrCrowley » Fri Jan 02, 2009 12:56 am

It probably only matters for super long barrels (like 30'+) anyway.
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Unread postAuthor: kenbo0422 » Wed Oct 14, 2009 11:06 am

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.
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Unread postAuthor: Ragnarok » Wed Oct 14, 2009 11:16 am

@kenbo0422: Those are for aerodynamic drag (i.e. air resistance), NOT contact friction.
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Unread postAuthor: kenbo0422 » Wed Oct 14, 2009 11:30 am

Oops... I misread the question....
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Re: Ammo GGDT calculations

Unread postAuthor: jimmy101 » Wed Oct 14, 2009 2:04 pm

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.
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