Someone Please Explain!!!!!
I know that this is an over asked question, and I also know that I am not the "Sharpest Nail" in the bucket, but can anyone out there in "Expert Land" please explain the term "Ballistic Coefficient" to me?
I already know the nuts and bolts explanation of what it is, but for the life of me, I can not wrap my mind around what it is supposed to mean, in relationship to the bullet flying on it's path. I understand it has to do with the bullet sectional density, and how it relates to the velocity of said bullet, but what do the numbers mean, and why are they important?
Thanks for any help.
BigBarn[:o)]
"Respect the land, and it will respect you"
I already know the nuts and bolts explanation of what it is, but for the life of me, I can not wrap my mind around what it is supposed to mean, in relationship to the bullet flying on it's path. I understand it has to do with the bullet sectional density, and how it relates to the velocity of said bullet, but what do the numbers mean, and why are they important?
Thanks for any help.
BigBarn[:o)]
"Respect the land, and it will respect you"
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BC is a measure of the air drag, the more streamlined the bullet the higher the BC (in a given caliber). A bullet of a "standard" profile slows at a known rate (B.C. = 1.000), the bullet your looking at slows at a different rate. A bullet with a BC of .500 slows twice as fast as a standard bullet, with a BC of .250 it will slow 4 times as fast, etc.
Yes, some bullets have a BC greater than 1.
SD is a weight/caliber ratio thing, IE: all 150gr 30cal bullets will have the same SD, regardless of shape. The higher the SD the deeper the potential penatration
Some guys like a mag full of lead, I still prefer one round to the head.0 -
BigBarn,
As simply as I can explain it, BC is a number that represents the efficiency of the bullet moving through the air in relationship to other bullets.
From Chuck Hawks:
"Ballistic Coefficient (BC) is basically a measure of how streamlined a bullet is; that is, how well it cuts through the air. Mathematically, it is the ratio of a bullet's sectional density to its coefficient of form. Ballistic Coefficient is essentially a measure of air drag. The higher the number the less drag, and the more efficiently the bullet cuts through the air. So for purposes of flying through the air efficiently, the bigger the BC number the better.BC is what determines trajectory and wind drift, other factors (velocity among them) being equal. BC changes with the shape of the bullet and the speed at which the bullet is traveling, while sectional density does not. Spitzer, which means pointed, is a more efficient shape than a round nose or a flat point. At the other end of the bullet, a boat tail (or tapered heel) reduces drag compared to a flat base. Both increase the BC of a bullet."
Best.
ADDED:
This is a piece of another pretty good explanation. The link is at the end:
What is Ballistic Coefficient and How is it Calculated?
"Simply stated, the ballistic coefficient is a measure of how well a projectile behaves in air. The ballistic coefficient is an important and useful concept that relates the drag deceleration of a given projectile to the drag deceleration of a standard bullet. The concept of the standard bullet and related ballistic coefficients was a major step forward, because otherwise the drag characteristic of every type of bullet fired would have to be measured individually - an impossible undertaking."
http://www.loadammo.com/Topics/September01.htm
And another good explanation:
http://www.reloadingroom.com/page42.html0 -
Hi BigBarn,
Good question and a very complicated question to explain simply.
I wouldn't fret too much about the definition, just keep in mind that the smaller the ballistic coefficient (BC) of a bullet, the greater its air resistance (drag). The greater the air resistance the less efficient the bullet. Conversely, the higher the BC of a bullet, the less its air resistance. In other words, a bullet with high BC is more aerodynamic than a bullet with low BC. A more aerodynamic bullet will have a flatter trajectory and retain more velocity.
Ballistic research showed that the effect of air resistance on a bullets motion depended on four factors:
1.Bullet shape and diameter
2.Velocity
3.Air density
4.The local velocity of sound
Now the next part all Americans hate to admit, but in 1898 a French Commission, called the Garve Commission, finally calculated the solution for a detailed drag function for a bullet. Note the term "function".
"Function" means the BC is constantly changing depending upon the physical parameters the bullet encounters while it is in motion. That means the BC is variable while the bullet is in flight and is called the effective BC (EBC). Change the temperature and the BC will change, change the air density, the BC changes, change the elevation, the BC changes, etc. This is far too complicated and requires a computer to compute, but this is how the ballistic tables are developed. The BC listed on most reloading tables is just the starting point and why you should not worry about the definition. Just remember what the BC means from a practical standpoint.
The actual definition of the BC (not the effective BC) is:
C=W/id^2
C=Ballistic coefficient (it is usually referred to as "C")
W=Mass of the bullet in pounds
i=factor related to the shape of the bullet (unitless)
d=caliber of the bullet (d^2 means diameter squared)
Regards,
Heavyiron
"If I don't see you nomore on this world, I'll meet you on the next one, and don't be late!" - Jimi Hendrix0 -
i know its hard to superscript a 2 on this board, but im looking over that math equation and want to make sure i got it right.
C=W/id2(superscripted)
id....i was always taught whenever there isnt a space between to functions, that automatically means x.
so is your equation:
C=W/ixd2?
former air operations officer SEAL Delivery Vehicle Team 2. former navy skeet team, former navy rifle/pistol team member. co-owner skeetmaster tubes inc.. owner/operator professional shooting instruction. NRA certified instructor.0 -
quote:Originally posted by bobski
i know its hard to superscript a 2 on this board, but im looking over that math equation and want to make sure i got it right.
C=W/id2(superscripted)
id....i was always taught whenever there isnt a space between to functions, that automatically means x.
so is your equation:
C=W/ixd2?
former air operations officer SEAL Delivery Vehicle Team 2. former navy skeet team, former navy rifle/pistol team member. co-owner skeetmaster tubes inc.. owner/operator professional shooting instruction. NRA certified instructor.
Correct.
Ted Kennedy's car has killed more people than my gun.0 -
Hi Bobski,
Yes, you have it right. In text it is something like, the weight of the bullet in pounds divided by the caliber squared and multiplied by i or C=W/i x d^2.
It is really difficult to cypher on the board - its not math friendly. The "^" symbol is used in Microsoft Excel formulas to denote a number raised to some power like 3^3 is 3 cubed or 4^2 is 4 squared. Its tough without superscript.
This above formula can also be simplified to the following:
C=SD/i (SD divided by i)
Where:
C= Ballistic coefficient
SD=Sectional Density (unitless)
i=Factor related to the shape of the bullet
The formula is simplified because SD=W/d^2.
Hope this helps.
Regards,
Heavyiron
"If I don't see you nomore on this world, I'll meet you on the next one, and don't be late!" - Jimi Hendrix0 -
P.S.
Here is a link to some equations that are good references to this thread.
http://www.eskimo.com/~jbm/equations/secdens.html
Heavy
"If I don't see you nomore on this world, I'll meet you on the next one, and don't be late!" - Jimi Hendrix0 -
So what bullets have BC's greater than 1, pray tell? The very best of the match rifle bullets are not greater than .600, to the best of my knowledge. 0 -
Bleu
Look at the SPBT projectles that go from 50cal on up to the 16" naval guns[:D] Didn't say they were for common calibers[}:)].
The smaller the bore size the lower the BC tends to be, the larger the bore the higher.
Some guys like a mag full of lead, I still prefer one round to the head.0 -
actually some match pills are into the .7's (lost river, and Kirby Allens new "allen magnum" super low drag pills that he is having made by hand right now, and a few others)
the quick and dirty version (as my cohorts have done the scientific meaning justice) is this;
BC- a bullets ability to overcome wind and drag though it's flight path while it's velocity decreases. (the JustC version). A longer bullet, will have a higher BC than a shorter bullet in a given dia bore size. The longer, and therefore heavier bullet, will retain more energy over distance (physics 101). therefore, the longer pills will fight the wind and drag more due to them retaining energy for longer periods. It is not worth really looking into BC until one wishes to jump past the intermediate range of 300yds or so. Hope that helps.
why chase the game when the bullet can get em from here?....
Got Balistics?0
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