# Ballistic coefficient



## ac700wildcat (Oct 30, 2006)

Someone please explain how you find it for a certain bullet and what effects different ones have. I'm new to reloading and would like to know a little more about my bullet choices. Right now I am working on a load with 150gr Hornady SST's. The bc for them is 0.415. What would happen if I changed to Hornady's 150gr SP with a bc of .338??

Thanks,
Matt


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## Horsager (Aug 31, 2006)

BC means basically squat until you stretch to 600yds and beyond, let's assume you're at least comparing pointed/spitzer bullets.

Check out this site, it's an easy to use free Ballistics calculator.

http://www.biggameinfo.com/index.aspx?page=/balcalc.ascx

I ran your numbers @ 3000fps. The lower BC bullet drops more as follows.

400 -1.8"
500 -4.5"
600 -9.3"
700 -17.3
800 -30"

Those numbers are extra inches of drop over and above the bullet with the .415 BC. You get to 600yds before you miss a 6" kill zone.

BC is basically a measure of aerodynamics. A bullet that is more aerodynamic will retain more velocity, thus it will travel further in a shorter amout of time as gravity is acting upon it (gravity is constant regardless of velocity). As I recall most bullet manufacturer's back into the BC number. That is they make the bullet, then they test the bullet and measure projectile drop vs. time of flight, then back into the BC number. Clear as mud?

I'll say it the easy way again. BC basically means squat under 600yds.


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## iwantabuggy (Feb 15, 2005)

Sorry Horsager, I have to go further with this.

Horsager is right about the trajectory, but lets not forget about energy. If you only consider trajectory you are only looking a part of the picture. You should also consider bullet construction as well, but you aren't asking about that.

Let's assume you wanted to hunt elk with this gun/load. Let's also assume that you agreed that 1500 ft/lbs of energy is a desired minimum for killing an elk. (Many may disagree, but for the sake of the example, assume you agree). The .415 BC bullet would be above 1500 ft/lbs out to around 410 yds or so. The .338 BC bullet would drop below 1500 ft/lbs somewhere around 335 yards.

Now let's assume you were hunting deer and that you agreed that 1000 ft/lbs would be an acceptable minimum energy. In this scenario you would drop below 1000 ft/lbs at around 630 yds with a .415 BC and at around 515 yds for the .338 BC. In this scenario it is pretty much a moot point for most shooters and hunting situations.

At hunting ranges, I believe energy is more important than bullet drop. Bullet drop can always be accounted for.

Think about it.


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## ac700wildcat (Oct 30, 2006)

Ok that helps. I just wasn't really sure what it would do to the path of the bullet in the air. I'm assuming that if the higher number decreases drop that it also helps the bullet drift less in a crosswind?

Really I have no real desire to shoot past even 500yds right now. My farthest kill in any hunting situation is only around 300yds, so I'll keep shooting and trying different bullets til I find a load i like.


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## Gohon (Feb 14, 2005)

Everything you want to know and more can be found here.

http://www.exteriorballistics.com/ebexplained/index.cfm


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## Horsager (Aug 31, 2006)

AC700, you are correct a bullet with a higher BC will also be less effected by the wind, again the variation in point of aim vs point of impact is determined by time of flight. Time of flight determines how much time the wind has to effect the bullet's trajectory.

Buggy, nice to see you've been reading Field & Stream, you've got that 1000/1500 number down pat. However I've killed enough deer with roughly 600 ft/lb of kenetic energy to know that I don't really need any more than that given proper bullet placement/construction.


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## iwantabuggy (Feb 15, 2005)

Horsager said:


> AC700, you are correct a bullet with a higher BC will also be less effected by the wind, again the variation in point of aim vs point of impact is determined by time of flight. Time of flight determines how much time the wind has to effect the bullet's trajectory.
> 
> Buggy, nice to see you've been reading Field & Stream, you've got that 1000/1500 number down pat. However I've killed enough deer with roughly 600 ft/lb of kenetic energy to know that I don't really need any more than that given proper bullet placement/construction.


Touche'. I didn't say that I agreed with the 1000/1500 ftlbs idea. I was just using it for purposes of illustration. It does take some amount of energy to bring game down. I too have killed game at much lower energies than many would agree is ethical (not me). Bullet placement is the most important, for sure. I once shot a 5 pt bull at over 500 yards with a Sierra Game King, 150 gr coming from a 7x57 at 2850 MV. The expected energy would have been in the ball park of 1000 ftlbs. The elk did a face plant when the bullet shattered his spine. 600 ftlbs would have done the same thing.

At some point however, the bullet will just bounce off like a bug on a windshield. I don't think anyone would want to be the one doing that, but I could be wrong.


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## Gohon (Feb 14, 2005)

> At some point however, the bullet will just bounce off like a bug on a windshield


Seems to me that would be a case of shooter error. At some point all bullets will fail to penetrate and bounce like a bug on a windshield.


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