Ballistic Coefficient

[GreyGhost85]

so with all the talk about ballistic coefficient lately and how it is crucial to finding you rifles true accuracy, i was wondering how to calculate it?? how do you find out what the B.C. of your bullet is?? most websites and ballistic tables i look at explain it but it never makes much sense...thanks..

[Red Rabbit]

BC really tells you how aerodynamic the bullet is, not how accurate. Bullet manufacturers will usually list the BC for their bullets on the web or in their reloading manual. Notice that Sierra lists the BC for different velocity ranges, as it changes with speed. Some BCs are calculated from bullet shape, and some are generated by actual shooting. Often, the actual BC by shooting will be lower than the mathematical ones.

 

A bullet with a higher BC is not necessarily more accurate. A bullet with a higher BC will drop less and drift less in the wind, but it may or may not group better than a bullet with a lower BC.

 

http://www.shootingsoftware.com/coefficients.htm

 

Hope I didn't muddy the water for ya.

 

RR

[firstcoueswas80]

Heavier bullets will have higher BC's and the larger daimeter bullets will ( for the most part)... i believe a .284 140 accubond is something like .485, where as the 277 140 acubond is .496, so this isnt always the case!

 

i think high BC's are more for the guys who wanna shoot at 500+ yards, when a heavier bullet with a higher BC takes advantage over a lighter bullet with more FPS behind it. i am happy with my set up, 140 accubond with a BC of .496 with a muzzle velocity of 3150.

[GreyGhost85]

thanks for the help...was able to find find my bullets B.C. on the Nosler website...now i can mess around with the ballistics calculators.....and the reason i was askning is because i am trying to get 800 yard accuracy out of my rifle....of course i plan on practincing at these ranges, but i figure i may able to save a little time and ammo, with having somewhere to start

[Hooked_on_Coues]

Shoot a group through a chrony at 10 yards, then do it again at 100 (if you trust yourself). There are several ballistics programs that will take this info and give you a true (true-er) indication of the actual BC.

 

I have found signaificant differences from advertised numbers, usually lower.

 

Reality is it won't make as much difference as the nut behind the trigger. Actual shooting at intended ranges will tell you everything you need to know.

[jamaro]

If the BC is basically the bullets ability to "buck" the wind would it make sense to use a heavier bullet? I know alot of us use bullet weights that are less than 170 grains for Coues deer because we get a flatter shooting bullet BUT if we went to a heavier bullet we would have a bullet that could fight the wind alot better. I would think that with todays range finders the need for a flatter shooting bullet is outweighed by a bullet that is going to be more consistent.

 

Any thoughts?

 

J-

[firstcoueswas80]

it is a measure of how it bucks the wind, and retained energy. most rifles and bullets will stay pretty decent within 500 yards with a lower BC. a higher BC helps retain energy and the bullet stay flatter after 500. most people who shoot heavy, high BC bullets are target shooters who shoot at like 1000 yards. they are usually too long to fit in normal hunting rifles ( ie th eBerger VLD)

[Schmitty]

Most all of what has been mentioned above is true.

 

As Doug stated it has to do with how "aerodynamic" a bullet is. Casey had it pretty much right, but the general rule of thumb is that the heavier the bullet for that specific caliber, the higher the BC will be. If you had two bullets that had the same weight, but were of different caliber, the smaller caliber bullet would have the higher BC. For example: a 140 grain 7mm Sierra gameking has a BC of .416 where as the 140 gr 6.5 mm gameking has a BC of .495. This is just a general rule, there are plenty of exceptions due to different bullet designs.

 

For most practical hunting purposes out to 500 yards., Velocity has more to do with bullet drop than anything else. Generally, the faster you drive a bullet, the less it will drop. BC does play role in bullet drop, but you usually don't see it until you pass the 400 yard mark.

 

As it was stated earlier. Today, with rangefinder's, Bullet Drop Compensating reticles and turrets, I find that the wind bucking ability is where the High BC bullets really shine. Let's face it, no matter what you're shooting, once a bullet passes the 350 yard mark, it starts to fall dramatically. This can be compensated for with quality modern equipment. Wind however is like the devil. It can come at you from any direction and at any speed and "reading" the wind is more like Black Magic than a proven science. The less I have to guess in regards to doping the wind the better off I and the critter I'm shooting at will be.

 

It's kind of cool to play around with the Ballistic Calculators and look at various scenarious with different bullets and calibers. I've found that they are fairly accurate when I've tested their results with my own range results within a couple of inches.

 

hope this helps,

Schmitty