Ballistic Coefficient (BC) - How important is it?

[PredatorSlayer]

Any bullet, no matter the caliber, with the same BC at the same velocity will drop/drift the same. It doesn't matter what brass is holding it or if it's .223 or .375.

That is what I thought.

 

[RockyMtnMT]

This is the difference between a .50 G1 BC and .65 G1 BC. Assumes same atmospheric conditions, velocity of 2800 fps and 10 MPH wind.
View attachment 171735View attachment 171736

Try this same exercise with the lower bc bullet being 20g lighter thus running 200 fps faster. This would be a good comparison of two bullets with similar form factor but the lighter one having less bc because of the weight. This sets up the rabbit and turtle race. Turtle always wins but in many cases he doesn't pass the rabbit until further down range than is needed.

 

[PredatorSlayer]

Try this same exercise with the lower bc bullet being 20g lighter thus running 200 fps faster. This would be a good comparison of two bullets with similar form factor but the lighter one having less bc because of the weight. This sets up the rabbit and turtle race. Turtle always wins but in many cases he doesn't pass the rabbit until further down range than is needed.

This is the same .50 G1 BC at 3000 fps. It is a little better, but it doesn't compensate 100% for the difference in BC - there is still a significant difference out past 600 yds.

 

[dfanonymous]

Is this true? In my mind a 350gr bullet with a .45 BC would have a lot of surface area to be moved around with the wind.

That's not how wind works. It does not blow your bullet. The vector angle of wind changes the angle of the bullet oringinal axis forces the rest of its flight in a weathervaning effect.
The bullet size in some calculators do change the prediction ever so slightly, I'm talking about .025 mils at around 1000 in different grain bullets at different calibers as far as wind deflection between a .308 and a .223. The two biggest factors in wind deflection is BC and velocity. This is why when we make a mph gun wind chart (the original hodnett quick wind) everyone will have a different mph gun depending on variety guns/ bullets being used.

 

[bruceleroy]

BC is THE determining factor for charting and predicting bullet performance downrange. Unless of course you want to fire hundreds of rounds and walk them into long range targets until you figure out how many clicks or how much Kentucky windage you need. It is literally the starting point for performance.

 

[RockyMtnMT]

This is the same .50 G1 BC at 3000 fps. It is a little better, but it doesn't compensate 100% for the difference in BC - there is still a significant difference out past 600 yds.

View attachment 171800

So in that comparison the heavier bullet takes over at about 500y. Good info.

 

[PredatorSlayer]

So in that comparison the heavier bullet takes over at about 600y. Good info.

Relative to what? Velocity? After 600 yards the higher BCs definitely pull away. There is a difference even at 300 yards. Whether or not its material depends on the game and the size of the kill zone.

 

[RockyMtnMT]

Relative to what? Velocity? After 600 yards the higher BCs definitely pull away. There is a difference even at 300 yards. Whether or not its material depends on the game and the size of the kill zone.

Sorry. You were quicker than my edit. I change to 500y.

The thought that I was trying to get out is the comparison of two similar bullets like say a 160g AB and a 140 AB in 7mm launched from a 7 mag. These would be very much the same form factor bullets.

 

[gohring3006]

Time of flight, energy on target and
trajectory.
I always look for the middle ground of these three factors. Sometimes the highest bc is not the best. Especially when velocity suffers from the heaviest bullets.
This is all with in practical hunting ranges of 1000 yards or less. After 1000 yards, it becomes more of a target shooting scenario for me, that's when I usually stick to the highest bc possible with in my cartridge capacity. All of it is velocity dependent.

 

[jebel]

I see where issues like fighting the wind come into the discussion of BC and its relative importance, as discussed above. But my own consideration of BC is a little different, when considering hunting bullets and their effectiveness at a given distance.

Personally, I begin my thinking with terminal effects. There seems to be an assumption throughout this entire discussion that all bullets under consideration have equal terminal effects, so the focus is only on external ballistics (how the bullet travels from the gun to the target).

I want to know the effective velocity range for the bullets I'm considering, which means I'm concerned about velocity. BC comes into the equation because it tells me what velocity I can expect at a given distance. I know that dialing for drop is relatively easy, as has been mentioned, but it's not the drop I'm focused on. It's the velocity. The velocity at distance (the result of BC) tells me my effective range in order to achieve the terminal effects on target that I'm looking for.

Also, I agree with the notion expressed above that in comparing different bullets, you should focus on like bullets from a terminal perspective. Said another way, you should compare the actual options you would use. For example, I wouldn't compare a 180 gr lead core bullet to a 180 gr monolithic, because I wouldn't choose between those two. The monolithic will penetrate better and have similar terminal effects when using 160 or 150 grains, so that's the bullet I'd compare to the 180 gr lead bullet.

Yes, I opened the terminal effects bucket of worms. My intent is not to derail this discussion, but only to explain how I (and maybe others) incorporate BC into my thinking when considering hunting bullets and their effective range.

 

[dfanonymous]

Relative to what? Velocity? I am looking at the wind too. In fact as stated in my original post, wind is more important than drop.

You're issue with wind has multiple components to it. Just keep in mind, no money or gear/components are going to make you or anyone else a better shooter, or wind caller without taking steps to learn how to data or dope the wind.

Second as eluded a higher BC bullet will have better ballistics. It's not arguable. This includes the wind. To understand, I recommend you look into lag time related to crosswind. Cross wind component is the only thing we as shooters care about for wind drift. So I'm not talking about any vertical components like AJ (aerodynamic jump).
Once you understand lag time, know that a higher BC will reduce this lag time. Next is velocity. There's a long explanation as to how this affects lag time but in short, a drag coefficient (not related to BC) is lower at a higher speed. This compressed lag time, and in short, the combination reduces your wind hold.

 

[L.Sherm]

I'm gonna give my 6.5x300wsm as example at 1,000 yards between the 140 and 156 both sighted in at 100 and 10mph cross wind.
140 3220 fps 219" drop and 56" of wind and t.o.f 1.25
156 at 3100fps 225" drop and 51" of wind and t.o.f. 1.25
Now tell me who's good enough to judge 5" of wind at 1000 yards across a canyon and who's not.
I'm not. Next tell me if .304 or .347 is better

 

[Danehunter]

Picky, picky, picky!
Guys, I was comparing two SIMILAR cartridges with two bullets of very different BCs. (i.e. nearly similar bullet weights and similar design)
Yes, I know we're talking bullets and not cartridges. Just using two well known cartridge examples. And we know most competitive PRS shooters no longer use .308 Win cartridges for this reason.

Eric B.

 

[PredatorSlayer]

You're issue with wind has multiple components to it. Just keep in mind, no money or gear/components are going to make you or anyone else a better shooter, or wind caller without taking steps to learn how to data or dope the wind.

Second as eluded a higher BC bullet will have better ballistics. It's not arguable. This includes the wind. To understand, I recommend you look into lag time related to crosswind. Cross wind component is the only thing we as shooters care about for wind drift. So I'm not talking about any vertical components like AJ (aerodynamic jump).
Once you understand lag time, know that a higher BC will reduce this lag time. Next is velocity. There's a long explanation as to how this affects lag time but in short, a drag coefficient (not related to BC) is lower at a higher speed. This compressed lag time, and in short, the combination reduces your wind hold.

Lag Time - you are talking about the difference in actual flight time with ballistic drag vs the hypothetical flight time in a vacuum correct?