could some one explain bullet coefficient

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Eric F

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bullet coefficient seems to come up on every topic that argues slow fat bullets versus small fast bullets. What is it how is it determined and what does it mean in the big world of bullets?
 
The ease at which a bullet Passes through the air. The .284 diameter Bullet Boat tail at 160 Grains has one of the best B.C. rates, it's around .556 The higher the number the better. Its about Drag, Boat tails usually have better BC than say a flat bottom. Ballistic Tips also do better than Round nose.
 
So how does this relate to bullet impact? and bullet performance after hitting a target?
 
Well, The higher the BC the Flatter the Trajectory. Impact Performance is completely different, usually game Bullets that Impact well and have less BC
 
If you had a Speer reloading Manual , in the back it has Exterior Ballistics table for Ballistic Coefficient's. It brings light to what your asking.
 
Technically speaking, the ballistic coefficient (b.c.) is just a measure of how well the bullet travels through air. Imagine the difference between a smooth round ball and a modern spitzer pointed boattail...or a flat disc flying face-on into the wind for that matter.

As it happens, a shape that travels easily through air will probably travel easily through other materials, at least until the bullet deforms/expands.
 
Add to the concept of ballistic coefficient that of sectional density. It conveys the ability for an object to overcome resistance. These are two very helpful descriptors for bullet performance. Read a good reloading manual and learn a lot more.
 
A bullet traveling at a thousand miles per hour in still air is in effect taking a thousand mile per hour wind head on. If it is long, sleek and pointed like the nose of a rocket it gets less wind resistiance and takes longer for it to slow down therefore it shoots flater. Blunt stubby pistol bullets are designed for short range and velocity drops off very rapidly no matter how fast they are started. Long pointy rifle bullets are able to maintain their velocity better.

As for sectional desity, immagine a sledge hammer with a head shaped like a disc, that is wider than it is long. It would not work nearly as well as a conventional sledge hammer that has a head shaped more like a beer can. The longer the shank of a bullet is in relation to the diamiter of the head, the more it can concentrate a large amount of force on one spot, and the better it can overcome wind resistiance.
 
There are three general areas of ballistic science:

1.) Internal Ballistics - what happens while the bullet is still inside the gun.
2.) Exterior Ballistics - what happens as the bullet flies thru the air.
3.) Terminal Ballistics - what happens once the bullet enters a body.

Bullet ballistic coefficient only comes into play in #2. The bullet’s sectional density and aspect ratio are relevant to all three. Though related, they are different concepts. Basically, as a rule, a long heavy bullet accelerates slower (#1), flies straighter (#2), and penetrates deeper (#3).
 
At the simplest level, the ballistic coefficient is a measure of the drag of the bullet in air.

All of the things mentioned above like sectional area and bullet shape are summarized in one number.
 
Ballistic Coeficient was originally an empirical measurement, based on a reference projectile. The BC of this projectile was defined as 1.

The BC of any other projectile is a measurement of how much faster or slower a projectile loses velocity relative to this standard projectile. The complication is that the BC changes with velocity, so if you really need to compare velocities, and be extremely precise, youneed the chart that has the BC in each velocity range, or at least supersonic/subsonic numbers.
 
Although a bullet with a higher ballistic coeeficient will travel farther, more importantly, it has much less drift.
If a bullet with a bc of .25 is going to drift 10 inches at a given distance. Then a bullet with a bc of .5 will drift half the amount (5 inches).
 
Fella's;

Also keep in mind that the B/C you see in the manuals is an average. The actual B/C is a (literal) moveable feast. In other words, B/C is not a constant. It can, and does, change as the bullet's velocity changes, ie, supersonic, trans-sonic, and subsonic.

900F
 
The .284 diameter Bullet Boat tail at 160 Grains has one of the best B.C. rates, it's around .556
Click to expand...

I just read in Shotgun News that specialized "match grade" 50 BMG bullets at 700 grains yield a B.C. value of just over 1.00. These guys stay supersonic out to 1,800 to 2,500 yards with drift of less than 3 inches in a 10mph cross wind at 1,000 yards.
 
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