Ballistic Co-efficient??
Hey Experts, can anyone out there explain the term "Ballistic Coefficient" to me? I see it being used all the time in reloading data articles, and have never seen it published with an explanation that I could understand.
Am I dense, or are there other out there that do not have a clue what the term means?
Thanks for you help,
BigBarn[:o)]
"Respect the land, and it will respect you"
Am I dense, or are there other out there that do not have a clue what the term means?
Thanks for you help,
BigBarn[:o)]
"Respect the land, and it will respect you"
0
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B.C. = the efficiency of the bullet to travel through the air, the higher the b.c. the less it is effected by wind i.e. 0 -
BB...... Ballistic Coefficient has to do with a bullets ability to cut throught the air. It is a measure if its sectional density as it relates to its form.
In short, thinner more pointed bullets have a better "Ballistic Coefficient" than wider more blunt shaped bullets.
"Never let school interfere with your education"0 -
They got it covered....its a measurement of air-drag.
Love them Pre-64's!!!!-Bob0 -
BigBarn, try to picture a blunt 30-30 soft point compared to a full metal jacket boat tail from a .308. If tou can visualize the shape of the projectiles then you might be able to understand how one will have less wind drag than the other.
If you really want to have a better understanding of ballistics, try a book called Understanding Firearm Ballistics. It is a great learning tool. CAUTION!!! some of it can be very boaring.[:D]
NEVER STOP TRYING TO LEARN. AND DONT BE AFRAID TO ASK QUESTIONS.
AC Tactical0 -
BC is a relative value assigned a projectile which is a function of it's weight VS length. The Bore size of any projectile can NOT be changed,..it has to fit through the barrel. Therefore,..a 7mm 168gr pill has a higher BC than a .308cal 168gr pill. Although both are the same weight,..the length of the 7mm bullet has to be LONGER in order to attain the same weight as the .308 cal projectile. This will also yield a higher Sectional Density.
High BC bullets are made for long range shooting. The higher a BC, the greater ability an object has to overcome DRAG created by the medium it is passing through (this being the air at any given altitude, density, humidity, temp, etc) The highest BC bullets are referred to as VLD's (Very Low Drag) Notice how long their bearing surfaces are,..as well as the Secant Ogive which is a very sharp taper with very little "rounding" of the nose profile. The sharp angle of the nose,..long length, and much longer Boat Tail with a much shallower angle (17-30degrees as compared to 35-40 degrees) allows these bullets to maintain their energy longer due to the fact that their sectional density and long shape allow them to,..
1. slice the air better due to a smaller bore size relative to weight
2. lose less elevation due to greater retained energy.
1 and 2 are directly related. let's look back at the 168gr 7mm and 30cal example. The smaller bore size of the 168gr 7mm allows it to cut through the air with less drag due to the fact that it is only presenting the air with a .284" frontal dia relative to a projectile of the same weight presenting a .308" frontal diameter. Physics dictates that if both objects are launched at the same MV,..then the smaller frontal mass object will retain energy longer due to it's smaller frontal mass not being affected as much by the drag of the air as is the larger frontal mass object. The larger frontal mass object and it's higher "drag" value,..I.E. Lower Balistic Coefficient will cause that air drag to decrease it's velocity,..and therefore it's energy at a greater rate. Therefore,..a Higher BC will allow any given projectile to shoot flatter due to it's greater retained energy. All this assumes a MV which is identical between 2 projectiles of equal weights/mass. If 2 projectiles of equal weight are fired,..the 168gr 7mm and 308cal,..and are fired at the same velocity,..then the higher BC of the 7mm bullet will cause it to fly flatter due to it's retaining energy over distance more than the 308cal projectile.
All this is important for only several main reasons,..
1. greater retained energy means less wind drift
2. greater retained energy means flatter trajectory which helps to keep the scope more centered in it's adjustment range due to having to take less "clicks" to get it on paper at 1000yds or whatever the chosen distance.
It all has to do with Long Range shooting/hunting. He who has the most streamlined bullet, with a high BC, and stable MV (low extreme spreads and low Standard Deviation) will fight the wind with more accuity and has the better chance at placing all 5 rounds close to one another on what one hopes will be the "x-ring"
why chase the game when the bullet can get em from here?....
Got Balistics?0 -
JustC;
I think you have explzined it absolutely, and I thank you very much. I believe that I have it fixed in my brain now, and will retain it forever! As long as the printer ink dosn't fade!
Thanks again,
BigBarn[:o)]
"Respect the land, and it will respect you"0 -
Most ballistic tables are based on various bullet shapes and some very low drag bullets do not correspond to the dated tables. In other words the the actual B.C. is will be higher than published and will drop less than expected at extended ranges. I have experienced this once with 139gr Hornady SST's in .284 diameter. They were chronographed and "should" have been dropping around 8" at 300 yds, it was actually closer to 6". This is a relatively small difference, but it can add up at long ranges. The only way to know for sure is test your loads at the long ranges, generally tables will get you close though. 0
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