Can you trust advertised ballistics coefficients? Mostly...but not always...

[entoptics]

I frequently use LabRadar data (shot tracking files from the SD card) to calculate ballistic coefficients using the JBM Ballistics web tool. Some of the results I got recently for a new rifle prompted me to post this as an FYI.

Here's a table of the 23 different bullets I've tested in the last couple of years, which have sufficient quality data to report, sorted from best to worst in terms of measured vs advertised...

Brand	Caliber	Bullet	Twist	Meas G1	Meas G7	Advert G1	Advert G7	Meas/Adv (%) G1	Meas/Adv (%) G7	n
Hornady	224	62 HPBT	8	0.291		0.274		106%		41
Hornady	308	225 ELDM	9	0.800	0.401	0.777	0.391	103%	103%	20
Hornady	264	143 ELDX	8	0.640	0.313	0.625	0.315	102%	99%	36
Sierra	308	190 SMK	9	0.544	0.271	0.533		102%		5
Hornady	284	175 ELDX	8	0.700	0.343	0.689	0.347	102%	99%	246
Nosler	243	90 AB	10	0.382		0.376		102%		8
Barnes	284	150 TTSX	8	0.454	0.225	0.450		101%		20
Berger	308	215 Hybrid	9	0.690	0.346	0.691	0.354	100%	98%	10
Hornady	308	208 ELDM	9	0.679	0.339	0.690	0.348	98%	97%	12
Hornady	308	208 ELDM	10	0.679	0.340	0.690	0.348	98%	98%	42
Nosler	277	140 AB	10	0.452		0.460		98%		9
Barnes	264	127 LRX	8	0.458	0.224	0.468		98%		16
Barnes	308	168 TTSX	10	0.451	0.226	0.470		96%		8
Barnes	284	145 LRX	8	0.466	0.234	0.486		96%		8
Nosler	277	150 ABLR	10	0.565		0.591		96%		4
Hornady	264	147 ELDM	8	0.661	0.325	0.697	0.351	95%	93%	93
Barnes	284	139 LRX	8	0.445	0.223	0.470		95%		9
Badlands	308	195 BDII	9	0.625	0.311	0.675	0.345	93%	90%	19
Badlands	284	140 BDII	8	0.516	0.259	0.560	0.287	92%	90%	18
Barnes	264	145 MB	8	0.647	0.321	0.703	0.350	92%	92%	11
Hammer	284	143 HH	8	0.399	0.200		0.230		87%	3
Hammer	284	140 AH	8	0.389	0.194		0.225		86%	5
Hammer	264	124 HH	8	0.413	0.202		0.245		82%	7

This data is all from tracking at least 100 yards, and uses atmospheric data from a Kestrel 3500 and my iPhone/Watch barometer. All bullets were fired from barrels with twist rates that were at or faster than recommended.

17 of 23 bullets were within 5% of quoted (18 if you count the 62 HPBT that was 6% better than quoted).
7 of 23 were better than quoted.
3 of 7 manufacturers had bullets that were consistently lower than quoted
2 of 7 manufacturers had no bullets within 7% of quoted
1 of 7 manufacturers had no bullets within 10% of quoted.

I may be a bit cynical, but I can't get past the feeling that some manufacturers are either incompetent or intentionally misleading when they provide a B.C. value that is so far off of reality. If I can get values within spitting distance of Berger/Hornady/Sierra/Nosler with a $600 consumer grade chronograph, a $150 weather meter, and a free online calculator, what possible excuse is there for advertising inaccurate B.C. values when you make bullets for a living?

For those that will say "Never Believe Anything! Validate with drops! Who cares about B.C.!" that's just silly.

We all use manufacturer provided data to make informed choices every day, and pretending otherwise is disingenuous. Would you shop at a gas station that required you buy the gas first, then confirm for yourself that they weren't shorting you 10% of the gas you thought you received?

 

[HARPERC]

For those that will say "Never Believe Anything! Validate with drops! Who cares about B.C.!" that's just silly.

I'm silly. All parts of the system need to be validated. Just me, You do you.

 

[MagnumManiac]

The BC numbers quoted are averages…you do realise BC is not constant, do you not?

Cheers.

 

[cohunt]

I wonder if you took 1 bullet-- let's say the 215 berger-, shot it in a 300bo subsonic, a 308w, a 30-06, 300wm, and a 300rum
What kind of differences you might see.

 

[FEENIX]

I frequently use LabRadar data (shot tracking files from the SD card) to calculate ballistic coefficients using the JBM Ballistics web tool. Some of the results I got recently for a new rifle prompted me to post this as an FYI.

Here's a table of the 23 different bullets I've tested in the last couple of years, which have sufficient quality data to report, sorted from best to worst in terms of measured vs advertised...

Brand	Caliber	Bullet	Twist	Meas G1	Meas G7	Advert G1	Advert G7	Meas/Adv (%) G1	Meas/Adv (%) G7	n
Hornady	224	62 HPBT	8	0.291		0.274		106%		41
Hornady	308	225 ELDM	9	0.800	0.401	0.777	0.391	103%	103%	20
Hornady	264	143 ELDX	8	0.640	0.313	0.625	0.315	102%	99%	36
Sierra	308	190 SMK	9	0.544	0.271	0.533		102%		5
Hornady	284	175 ELDX	8	0.700	0.343	0.689	0.347	102%	99%	246
Nosler	243	90 AB	10	0.382		0.376		102%		8
Barnes	284	150 TTSX	8	0.454	0.225	0.450		101%		20
Berger	308	215 Hybrid	9	0.690	0.346	0.691	0.354	100%	98%	10
Hornady	308	208 ELDM	9	0.679	0.339	0.690	0.348	98%	97%	12
Hornady	308	208 ELDM	10	0.679	0.340	0.690	0.348	98%	98%	42
Nosler	277	140 AB	10	0.452		0.460		98%		9
Barnes	264	127 LRX	8	0.458	0.224	0.468		98%		16
Barnes	308	168 TTSX	10	0.451	0.226	0.470		96%		8
Barnes	284	145 LRX	8	0.466	0.234	0.486		96%		8
Nosler	277	150 ABLR	10	0.565		0.591		96%		4
Hornady	264	147 ELDM	8	0.661	0.325	0.697	0.351	95%	93%	93
Barnes	284	139 LRX	8	0.445	0.223	0.470		95%		9
Badlands	308	195 BDII	9	0.625	0.311	0.675	0.345	93%	90%	19
Badlands	284	140 BDII	8	0.516	0.259	0.560	0.287	92%	90%	18
Barnes	264	145 MB	8	0.647	0.321	0.703	0.350	92%	92%	11
Hammer	284	143 HH	8	0.399	0.200		0.230		87%	3
Hammer	284	140 AH	8	0.389	0.194		0.225		86%	5
Hammer	264	124 HH	8	0.413	0.202		0.245		82%	7

This data is all from tracking at least 100 yards, and uses atmospheric data from a Kestrel 3500 and my iPhone/Watch barometer. All bullets were fired from barrels with twist rates that were at or faster than recommended.

17 of 23 bullets were within 5% of quoted (18 if you count the 62 HPBT that was 6% better than quoted).
7 of 23 were better than quoted.
3 of 7 manufacturers had bullets that were consistently lower than quoted
2 of 7 manufacturers had no bullets within 7% of quoted
1 of 7 manufacturers had no bullets within 10% of quoted.

I may be a bit cynical, but I can't get past the feeling that some manufacturers are either incompetent or intentionally misleading when they provide a B.C. value that is so far off of reality. If I can get values within spitting distance of Berger/Hornady/Sierra/Nosler with a $600 consumer grade chronograph, a $150 weather meter, and a free online calculator, what possible excuse is there for advertising inaccurate B.C. values when you make bullets for a living?

For those that will say "Never Believe Anything! Validate with drops! Who cares about B.C.!" that's just silly.

We all use manufacturer provided data to make informed choices every day, and pretending otherwise is disingenuous. Would you shop at a gas station that required you buy the gas first, then confirm for yourself that they weren't shorting you 10% of the gas you thought you received?

I know you posted this with the best intentions, but the intent often gets lost. I appreciate you. Cheers!

 

[Doom2]

Ballistic coefficient is a factor that is used to estimate the coefficient of drag as compared to a specific bullet shape. The coefficient of drag is a function of velocity/Mach Number. Since most bullets do not conform to the specific drag models so they do not behave over a large range of velocities as the models so the BC ends up being a function of velocity (see Brian Ritz and custom drag models). Since most published numbers are quoted without any reference to velocity it must be treated with some degree of skepticism since we don't know the velocity range over which the BC was determined.

Hornady has refined their BC for the ELD's and Sierra publishes a velocity range for all of their BC's. Unfortunately, bullets are a commodity and marketing is marketing. The better the seller can make his product look the better. That often comes at the expense of the whole truth.

 

[biednick]

This data is all from tracking at least 100 yards, and uses atmospheric data from a
If I can get values within spitting distance of Berger/Hornady/Sierra/Nosler with a $600 consumer grade chronograph, a $150 weather meter, and a free online calculator, what possible excuse is there for advertising inaccurate B.C. values when you make bullets for a living?

Velocity. BC drops with velocity. If you're testing with a different muzzle velocity than the manufacturer you'll get a different result. Sierra is the only manufacturer I've seen give different BCs for different velocity ranges with the same bullet.

Twist rate indirectly plays a part too. A bullet that's marginally stable will have a lower BC than a bullet that's very stable.

That's a big part of the reason it's important to true your calculator with actual drops instead of relying on published values. Even if the BC is dead on in the 0-100yd range, it's probably going to be significantly lower by 1000yd. Advertised BCs should get you close enough to true your solution with minor MV or BC tweaks.

At the end of the day it's unreasonable to expect published BCs to line up perfectly with the actual BC you see. There's too many variables other than the bullet to provide a precise BC.

I use the same BC calculator you linked for cast bullets, and always run something with a published BC through it so I know my atmospheric values are at least close to correct. Some of the bullets you have within 2% are off by 5% or more when I shoot them. I use the same setup (kestrel and labradar). Neither of us are necessarily wrong, we're just shooting the sambe bullet differently and getting different results. I've also seen a meaningful difference shooting the same bullet from the same lot in 2 guns with different muzzle velocities.

 

[BrentM]

I don't have any major issues with advertised out to about 1000. I have had to tweak some but in general it's minimal.

 

[ridgewalker]

WOW! My old shoulder hurts just seeing all those shots! That's a lot of work, but now you have an excellent idea of what each of your guns/loads are doing. Great job!
Question: will you repeat using my guns/cartridges? Just teasing!

 

[waveslayer]

Great info and thanks for testing. All that info is already out there. BC's are velocity dependent, so the advertised are always off.. that's why you TRUE your calculators to your rifle. 100-600 yards you true the velocity despite what the chrono says, after about 800 yards you tweak your BC.

Stated BC's are great starting points, that's all. But good info above just again you prove that each rifle has to be trued to what the target is telling you

 

[CPorter]

I frequently use LabRadar data (shot tracking files from the SD card) to calculate ballistic coefficients using the JBM Ballistics web tool. Some of the results I got recently for a new rifle prompted me to post this as an FYI.

Here's a table of the 23 different bullets I've tested in the last couple of years, which have sufficient quality data to report, sorted from best to worst in terms of measured vs advertised...

Brand	Caliber	Bullet	Twist	Meas G1	Meas G7	Advert G1	Advert G7	Meas/Adv (%) G1	Meas/Adv (%) G7	n
Hornady	224	62 HPBT	8	0.291		0.274		106%		41
Hornady	308	225 ELDM	9	0.800	0.401	0.777	0.391	103%	103%	20
Hornady	264	143 ELDX	8	0.640	0.313	0.625	0.315	102%	99%	36
Sierra	308	190 SMK	9	0.544	0.271	0.533		102%		5
Hornady	284	175 ELDX	8	0.700	0.343	0.689	0.347	102%	99%	246
Nosler	243	90 AB	10	0.382		0.376		102%		8
Barnes	284	150 TTSX	8	0.454	0.225	0.450		101%		20
Berger	308	215 Hybrid	9	0.690	0.346	0.691	0.354	100%	98%	10
Hornady	308	208 ELDM	9	0.679	0.339	0.690	0.348	98%	97%	12
Hornady	308	208 ELDM	10	0.679	0.340	0.690	0.348	98%	98%	42
Nosler	277	140 AB	10	0.452		0.460		98%		9
Barnes	264	127 LRX	8	0.458	0.224	0.468		98%		16
Barnes	308	168 TTSX	10	0.451	0.226	0.470		96%		8
Barnes	284	145 LRX	8	0.466	0.234	0.486		96%		8
Nosler	277	150 ABLR	10	0.565		0.591		96%		4
Hornady	264	147 ELDM	8	0.661	0.325	0.697	0.351	95%	93%	93
Barnes	284	139 LRX	8	0.445	0.223	0.470		95%		9
Badlands	308	195 BDII	9	0.625	0.311	0.675	0.345	93%	90%	19
Badlands	284	140 BDII	8	0.516	0.259	0.560	0.287	92%	90%	18
Barnes	264	145 MB	8	0.647	0.321	0.703	0.350	92%	92%	11
Hammer	284	143 HH	8	0.399	0.200		0.230		87%	3
Hammer	284	140 AH	8	0.389	0.194		0.225		86%	5
Hammer	264	124 HH	8	0.413	0.202		0.245		82%	7

This data is all from tracking at least 100 yards, and uses atmospheric data from a Kestrel 3500 and my iPhone/Watch barometer. All bullets were fired from barrels with twist rates that were at or faster than recommended.

17 of 23 bullets were within 5% of quoted (18 if you count the 62 HPBT that was 6% better than quoted).
7 of 23 were better than quoted.
3 of 7 manufacturers had bullets that were consistently lower than quoted
2 of 7 manufacturers had no bullets within 7% of quoted
1 of 7 manufacturers had no bullets within 10% of quoted.

I may be a bit cynical, but I can't get past the feeling that some manufacturers are either incompetent or intentionally misleading when they provide a B.C. value that is so far off of reality. If I can get values within spitting distance of Berger/Hornady/Sierra/Nosler with a $600 consumer grade chronograph, a $150 weather meter, and a free online calculator, what possible excuse is there for advertising inaccurate B.C. values when you make bullets for a living?

For those that will say "Never Believe Anything! Validate with drops! Who cares about B.C.!" that's just silly.

We all use manufacturer provided data to make informed choices every day, and pretending otherwise is disingenuous. Would you shop at a gas station that required you buy the gas first, then confirm for yourself that they weren't shorting you 10% of the gas you thought you received?

Since BC changes with velocity, what velocity range did you pick versus what the manufacturer picked?

This is for a .308 hpbt

 

[waveslayer]

Since BC changes with velocity, what velocity range did you pick versus what the manufacturer picked?

This is for a .308 hpbt

View attachment 482652

Pick one... doesn't matter. Go out and shoot! Then line your calculator up to your data and what the target says. Then when it adjust (the calculator ) that's the BC to use. Hence why CDM's are the way to go and the future

 

[Pdvdh]

I do the same thing with my LabRadar
There's no better method to determine bullet BC value than tracking the downrange rate of velocity loss.

It eliminates sources of error associated with the use of measured downrange drops. One manufacturer of bullets with amongst the largest error in advertised BC values uses measured drops to establish an estimated BC value. That should tell something about the lack of accuracy of that method. Simply too many associated sources of error.

I've been able to detect defective bullets by monitoring velocity loss over the first 80-100yds of bullet travel with LabRadar. When a bullet strikes well outside my group on paper, I now review its velocity loss. If its rate of velocity loss is notably faster than the average rate of velocity loss for the other bullets fired, I know that bullet had some increased wobbling or some other defect in flight that increased its wind drag during flight.

I've also had entire boxes of copper mono bullets that shot 22" groups at 280 yds from a rifle that shot 5 other brands of bullets into less than 1/2 moa. When I compared my calculated BC for that defective bullet to the manufacturer's advertised BC value, it was miserably lower than advertised. I notified the manufacturer of the problems. They sent me another box of bullets two times. Same lack of BC value and precision. They eventually confirmed that they had received a defective batch of copper rod that had been bent during shipment to their shop. Which resulting in bent/banana shaped bullets after turning them down in their lathes.

Another example..., I've used LabRadar to determine two different caliber bullets from one manufacturer were so BC value inflated that they wouldn't maintain expansion velocity to my required 600yd hunting distance. Even though they shot well enough, I had no confidence they'ld expand on impact at my 600yd shot yardage. So I didn't bother wasting components and my time shooting either bullet downrange any further, after confirming the BC values with the LabRadar.

I recognize that most shooters lack the interest and/or ability to use their LabRadar in this fashion. In fact, the majority of hunters buy and shoot factory ammo. Most reloaders won't take the time to determine their bullet BC value in their personal rifles using downrange LabRadar velocity data. Even if they already own a LabRadar. This doesn't diminish the value of LabRadar calculated BC values. Just means most shooters are happy with their methods and not about to change their methods, for whatever reasons... like "I don't wanna complicate my shooting enjoyment with tedious LabRadar calculations..."

I can already see from the posted responses, most are quickly looking for any reason to reach the conclusion there's no value in calculating LabRadar velocity-based bullet BC values. They've never done it. And aren't about to. No matter what.

Which explains the "whatever..." nature of the responses being posted.

And I've just gained a huge fan base! Haha...

 

[entoptics]

To those in the "Verify everything" crowd...I do. Where do you think all this data is coming from?

To the "B.C. changes with velocity, so therefore we can know nothing" crowd...

These are rifle bullets. For hunting. I'd say it's fairly safe to assume rifle speeds. In my case, almost all of these bullets were fired between 2850 fps and 3000 fps, which by most sources would actually be near the maximum B.C. Take a look at Sierra's or Hornady's or Litz's multiple B.C. data for just about any bullet and you'll see that's the case.

So what sort of variation with velocity is normal? From Bryan Litz himself...

Bullet	G1 3000-2500	G1 2500-2000	Variation	G7 3000-2500	G7 2500-2000	Variation
142 NABLR	0.595​	0.577​	3%​	0.295​	0.290​	2%​
140 ELDM	0.659​	0.635​	4%​	0.327​	0.319​	2%​
200 ELDX	0.632​	0.61​	4%​	0.313​	0.307​	2%​
105 Hybrid	0.558​	0.539​	3%​	0.277​	0.271​	2%​

I'd say that we actually can know something about B.C., at least enough to perform basic comparisons amongst similar projectiles prior to shooting dozens of them...Well, at least we could if the manufacturers would value reality over marketing.