How are BCs Used to Calculate Drops & drifts?

[davidjoe]

Try shooting in the same direction as the earth's rotation and then shooting the opposite direction of the earth's rotation and see the difference in point of impact on say a 1000yd target in each direction......the points of impact are not the same.

Not everything that affects a bullet is “BC”. Shooting upward, downward, wind against the direction of spin drift, the earth’s rotation, are examples. Wind, humidity, temperature, density, altitude and other environmental things clearly affect flight but they do not change the BC assigned to the bullet, they simply affect where it is predicted to impact.

Some things unique to “a particular bullet from a particular gun, as opposed to all bullets that might be shot” actually do affect BC, but still are not BC — Angle of attack, instability, over stabilization, precession, yaw, riffling indentations, defects, and jacket damage.

BC as I understand it is how an ideal example of the bullet in question maintains its path, in relation to how a known bullet does, - often it’s the 1.0 pound, flat base, fairly blunt tangent ogive design that is maybe 4 calibers long, if memory serves.

 

[gpoldblue]

Not everything that affects a bullet is “BC”. Shooting upward, downward, wind against the direction of spin drift, the earth’s rotation, are examples. Wind, humidity, temperature, density, altitude and other environmental things clearly affect flight but they do not change the BC assigned to the bullet, they simply affect where it is predicted to impact.

Some things unique to “a particular bullet from a particular gun, as opposed to all bullets that might be shot” actually do affect BC, but still are not BC — Angle of attack, instability, over stabilization, precession, yaw, riffling indentations, defects, and jacket damage.

BC as I understand it is how an ideal example of the bullet in question maintains its path, in relation to how a known bullet does, - often it’s the 1.0 pound, flat base, fairly blunt tangent ogive design that is maybe 4 calibers long, if memory serves.

A headwind will certainly slow a bullet and a tailwind will certainly help the bullets' range. When that bullet leaves the muzzle,it's traveling about 1800mph or more....that's a helluva headwind all by itself say nothing about ambient conditions. Just think what the B.C. would be in space!! B.C. does vary as the speed varies.
Anything that affects the bullets flight,affects the the bullets B.C. B.C. is the bullets relationship to the effects of the environment including what happens to the bullet inside the barrel. If the bullet is deformed inside the barrel, and comes out unstable,the B.C. has been altered. B.C. is the bullets ability to overcome the environment.

 

[DocUSMCRetired]

Try shooting in the same direction as the earth's rotation and then shooting the opposite direction of the earth's rotation and see the difference in point of impact on say a 1000yd target in each direction......the points of impact are not the same.

The BC isn't changing with direction of fire. Their is both a horizontal and vertical component to Coriolis, plus Aerodynamic Jump would reverse itself as well doing this.

I believe that the BC number assigned to a bullet need not consider any external variables at all.

BC does have external factors. Dynamic & Gyroscopic Stability effect the BC. When your SG is between 1.0 - 1.5 each 0.1 SG is around 3% BC loss.

BC is a comparison of the bullets performance vs the standard. BC also fluctuates depending on your velocity and bullet design. So it will not match consistently at all velocities which is why we used to use Segmented BCs. Now we no longer use BCs. We use actual flight models.

 

[Brians356]

Not following this. With each layer of paper, wouldn't the SA increase? The inside of the strip would have the same SA as the sphere, but the outside SA would be more. Conundrum theories abound...

He was just providing a visualization cue, wrapping paper exactly once around a sphere. Consider a cylinder with diameter and length both equal to a sphere's diameter. Their curved surface areas are equal (not counting the two ends of the cylinder).
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[Richard Jones]

^^^^
Visualization. To what end?
I guess I just don't understand the relevance of the 'statement'. Calculating the SA of the sphere is easy. We are picking nits, right?

 

[Brians356]

^^^^
Visualization. To what end?
I guess I just don't understand the relevance of the 'statement'. Calculating the SA of the sphere is easy. We are picking nits, right?

Not with me, you're not. It was @davidjoe who described wrapping paper around a sphere, and you said "Not following this. With each layer of paper, wouldn't the SA increase?". (Answer: No, there's only one layer.) I tried to help you follow it. (Something about no good deed going unpunished.)
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