Are you thinking of BC the wrong way?

[DocUSMCRetired]

Are you programmed to incorrectly picture what a BC should look like?

What do you think of when you think of a BC? Does a simple one number solution come to mind? Or do you picture a velocity band? When you talk about the BC of a bullet, it is important to make sure that you don’t forget the other half of that number. A BC should always be followed by an indicator. It is not just enough to call upon a single number. By using a single number you don’t see the entire performance of the bullet. You also don’t get a fair comparison of one product to another. Making it easy to push a little marketing hype in to what the consumer thinks. This can also hide a bullets true performance, and some bullets have a wide variation in BC from Mach 2.5+ to Mach 0.9-(Subsonic), while others are more consistent. Anytime you see a BC you should be asking yourself “at what velocity”. All BCs published by Applied Ballistics are averaged from 3000 fps to 1500 fps. Averaged is the key word here. It is important that the consumer understands comparing apples to apples. You cannot take a Mach 2.5 or high BC and compare it an averaged BC or a Mach 2.0 or Mach 0.9 BC etc.

A BC is only true at 1 specific velocity, which is why you can find velocity bands published in the Ballistic Performance Book, but also why you can twist a little marketing hype in to them by using the highest performing velocity band as the published BC on the box. (You can hide a bullets flaws this way) As Bryan put it "The BC changes a lot over the flight of the bullet."

As a shooter anytime you see a BC you should be seeing 2 indicators. Think of it like when you look at a cars mpg. The cars list “## highway, ## city”. Well a BC should say “## G7 Averaged” or “## @ Mach 2.5 & ## @ Mach 1.0 & etc. “. You could use ## G7 @ 2800 fps, and it would be just fine. As long as you know where in the velocity band that BC was calculated at, it allows for a more honest comparison against other bullets. So the next time you see a BC the first question that pops in to your head should be “where is the rest of the story” followed by asking the question “at what velocity”.

Of course, if you use Applied Ballistics CDMs you don't have to worry about velocity effects of BC as your bullets drag is being modeled all together. Giving you not only a more accurate prediction, but also removing any marketing bias. However we know it can be hard to compare bullets on the shelf this way. So it is still important every time you see "BC G# 0.###" that you ask yourself "At what velocity".

 

[hdwhit]

DocUSMCRetired wrote:
Are you thinking of BC the wrong way?

No.

But then, I hardly think of Ballistic Coefficient (BC) at all.

As a measure of how well the bullet overcomes air resistance, the BC is dependent on the configuration of the bullet. Given that the calibers I load have a limited number of bullet weights and configurations in the weights that I am interested in for use over the distances that I will shoot them, it long ago became apparent to me that empirical testing of various bullets and loads to determine the one that provided me the greatest overall utility was going to be the best approach for me. So, the last time I consulted a BC table (and I have books full of them) was 1980.

 

[someguy2800]

After testing 3 bullets in the real world recently to see what there true drop is compared to what the ballistic coefficient on the box predicts I concluded you can't trust marketing. Hornady always seams to have the highest BC listed on there bullets for a given bullet type but like you said they never say what velocity that is. I think it's BS

 

[Sunray]

"...I hardly think of Ballistic Coefficient (BC) at all..." Likewise. The Ballistic Coefficient of a bullet isn't something you can see either. It's a measure of air resistance. Doesn't mean a great deal.

 

[Laphroaig]

I find it interesting how close the G1 and G7 calculations are in the chart. It appears its not worth the trouble to try and find G7 BC's to plug into the trajectory models for boattails.

 

[egd]

When I think of BC I think of the comic strip. I miss it.

 

[jbmillard]

Are you programmed to incorrectly picture what a BC should look like?

I don't understand the chart. It would appear to be the CD of the drag functions as a function of mach number. The G7 drag function has a CD of 0.3440 at mach 1.5 and the G1 drag function has a value of 0.6573 at mach 1.5. The CDs of the drag functions are quite different, but your chart shows them as almost the same.

You can see the values for the G1 drag function here:

http://www.jbmballistics.com/ballistics/downloads/text/mcg1.txt

and the G7 here:

http://www.jbmballistics.com/ballistics/downloads/text/mcg7.txt

Very confusing.

 

[jmr40]

BC matters, but not for what most people think, it isn't trajectory, it's down range energy and wind drift. Lighter bullets with poor BC's can be shot faster and almost always shoot flatter at normal ranges. But heavier bullets with good BC's always impact faster at distance, are less effected by wind and cause more damage to game. Comparing 150 gr Hornady SST's from my 308 to the 178gr ELD-X bullets the 150's have a 200 fps advantage at the muzzle. But at 300 yards the 178 is the same speed with less than 2" more drop. And the SST's are a pretty high BC bullet. As range increases the 178's speed advantage grows, but you have to get WAAAAY out there before the 178's have less drop, if ever. But with today's range finders and optics bullet drop isn't nearly as important to hunters. It has never been important to target shooters shooting at known ranges.

I've seen some extreme examples of very good BC bullets compared to really poor BC bullets making a difference at as little as 50 yards My 30-06 loaded with some of the better BC 180 gr. bullets has more speed and energy beyond 100 yards than a 300 WM loaded with 180 gr RN bullets. More energy and speed at 300 yards than many 180 gr pointed bullets fired from 300 WM. The better BC 6.5 loads have more energy than 300 WM at 600+ yards. So yes, BC matters.

I recently read an article where an independent lab tested several popular bullets and determined the BC's were in many cases off. Most were within 5% which isn't really a big deal for most people, but others were off considerably, around 10% and sometimes more. Some actually had better BC's than advertised. And certain companies were consistently off. Hornady BTW, is currently using doppler radar down range to more accurately determine bullet speed. Their new ELD line of bullets listed BC's were among the most accurate according to the article I read.

Sierria does list BC's at different velocities. IIRC their claims were one of the more accurate in the study I saw. Nosler was the one bullet maker that was consistently optimistic with their BC claims.

But even with a 5%-10% error most hunters won't notice the difference. If a company lists a bullet with a BC of .650 and it is actually .620, most of us will never notice. But as a hunter shooting a bullet with a BC of .550 is a huge advantage over a bullet with a BC of .350. Even if the .550 bullet is off by 20%, it is still significantly better than the .350 BC bullet.

 

[DocUSMCRetired]

I don't understand the chart. It would appear to be the CD of the drag functions as a function of mach number. The G7 drag function has a CD of 0.3440 at mach 1.5 and the G1 drag function has a value of 0.6573 at mach 1.5. The CDs of the drag functions are quite different, but your chart shows them as almost the same.

You can see the values for the G1 drag function here:

http://www.jbmballistics.com/ballistics/downloads/text/mcg1.txt

and the G7 here:

http://www.jbmballistics.com/ballistics/downloads/text/mcg7.txt

Very confusing.

What you are seeing is the actual flight data from the 175 SMK. Not the curves for the G1 and G7 Standard.

 

[DocUSMCRetired]

I find it interesting how close the G1 and G7 calculations are in the chart. It appears its not worth the trouble to try and find G7 BC's to plug into the trajectory models for boattails.

What you are seeing is the Drag Curve for a specific bullet, not the standards. This bullet is a perfect example for one that shooters should be using a CDM for and not a BC for the most accurate prediction.

 

[DocUSMCRetired]

BC matters, but not for what most people think, it isn't trajectory, it's down range energy and wind drift. Lighter bullets with poor BC's can be shot faster and almost always shoot flatter at normal ranges. But heavier bullets with good BC's always impact faster at distance, are less effected by wind and cause more damage to game. Comparing 150 gr Hornady SST's from my 308 to the 178gr ELD-X bullets the 150's have a 200 fps advantage at the muzzle. But at 300 yards the 178 is the same speed with less than 2" more drop. And the SST's are a pretty high BC bullet. As range increases the 178's speed advantage grows, but you have to get WAAAAY out there before the 178's have less drop, if ever. But with today's range finders and optics bullet drop isn't nearly as important to hunters. It has never been important to target shooters shooting at known ranges.

I've seen some extreme examples of very good BC bullets compared to really poor BC bullets making a difference at as little as 50 yards My 30-06 loaded with some of the better BC 180 gr. bullets has more speed and energy beyond 100 yards than a 300 WM loaded with 180 gr RN bullets. More energy and speed at 300 yards than many 180 gr pointed bullets fired from 300 WM. The better BC 6.5 loads have more energy than 300 WM at 600+ yards. So yes, BC matters.

I recently read an article where an independent lab tested several popular bullets and determined the BC's were in many cases off. Most were within 5% which isn't really a big deal for most people, but others were off considerably, around 10% and sometimes more. Some actually had better BC's than advertised. And certain companies were consistently off. Hornady BTW, is currently using doppler radar down range to more accurately determine bullet speed. Their new ELD line of bullets listed BC's were among the most accurate according to the article I read.

Sierria does list BC's at different velocities. IIRC their claims were one of the more accurate in the study I saw. Nosler was the one bullet maker that was consistently optimistic with their BC claims.

But even with a 5%-10% error most hunters won't notice the difference. If a company lists a bullet with a BC of .650 and it is actually .620, most of us will never notice. But as a hunter shooting a bullet with a BC of .550 is a huge advantage over a bullet with a BC of .350. Even if the .550 bullet is off by 20%, it is still significantly better than the .350 BC bullet.

I am pretty certain you were looking at our study. Was it by Applied Ballistics? We have a full time lab that tests bullets constantly, and Bryan released a study similar to this years ago.

 

[horsey300]

BC matters, but not for what most people think, it isn't trajectory, it's down range energy and wind drift. Lighter bullets with poor BC's can be shot faster and almost always shoot flatter at normal ranges. But heavier bullets with good BC's always impact faster at distance, are less effected by wind and cause more damage to game. Comparing 150 gr Hornady SST's from my 308 to the 178gr ELD-X bullets the 150's have a 200 fps advantage at the muzzle. But at 300 yards the 178 is the same speed with less than 2" more drop. And the SST's are a pretty high BC bullet. As range increases the 178's speed advantage grows, but you have to get WAAAAY out there before the 178's have less drop, if ever. But with today's range finders and optics bullet drop isn't nearly as important to hunters. It has never been important to target shooters shooting at known ranges.

I've seen some extreme examples of very good BC bullets compared to really poor BC bullets making a difference at as little as 50 yards My 30-06 loaded with some of the better BC 180 gr. bullets has more speed and energy beyond 100 yards than a 300 WM loaded with 180 gr RN bullets. More energy and speed at 300 yards than many 180 gr pointed bullets fired from 300 WM. The better BC 6.5 loads have more energy than 300 WM at 600+ yards. So yes, BC matters.

I recently read an article where an independent lab tested several popular bullets and determined the BC's were in many cases off. Most were within 5% which isn't really a big deal for most people, but others were off considerably, around 10% and sometimes more. Some actually had better BC's than advertised. And certain companies were consistently off. Hornady BTW, is currently using doppler radar down range to more accurately determine bullet speed. Their new ELD line of bullets listed BC's were among the most accurate according to the article I read.

Sierria does list BC's at different velocities. IIRC their claims were one of the more accurate in the study I saw. Nosler was the one bullet maker that was consistently optimistic with their BC claims.

But even with a 5%-10% error most hunters won't notice the difference. If a company lists a bullet with a BC of .650 and it is actually .620, most of us will never notice. But as a hunter shooting a bullet with a BC of .550 is a huge advantage over a bullet with a BC of .350. Even if the .550 bullet is off by 20%, it is still significantly better than the .350 BC bullet.

On the Sierra note, I've noticed that if anything, they list the bc conservatively, but I didn't notice that until I started testing them at 400+ yds.