Inaccurate Specifications of Ballistic Coefficients

[RonAKA]

I stumbled across a paper written by Michael Courtney for the U.S. Air Force Academy on the issue of actual measurements of ballistic coefficients not achieving BC advertised by bullet manufacturers. It is a bit dated, 2012, so this may be old news for some. But I thought I would post it anyway. I think we get lulled into thinking we can plug these numbers into our computer and calculate to a tenth of an inch where the bullet impact will be at 300 yards. That may not be so based on this report. There are very significant differences between advertised and actual BC's.

The report dismisses the theory that bullet yaw caused by shooting out of a light sporter barrel is responsible. It also dismisses measurement error. That kind of leaves manufacturing tolerance issues where the bullet shape does not match the intended design, and simple optimistic calculation methods.

Out of curiosity I did a quick average of overestimation error by manufacturer. Here are the results:

MFG (samples) - % Overestimation
Federal (1) - 23.1
Nosler(11) - 17.4
Berger(7) - 12.3
Barnes(3) - 9.6
LC(2) - 7.9
Hornady(2) - 3.9
Speer(1) 1.6

Here is the link if you want to read the details. I did some quick checking of the specifications in this report and what the manufacturers are reporting today on line. Since the report was written in 2012, I thought perhaps some of the manufacturers may have changed their advertised BC's. Doesn't appear to be the case, although I only checked a few. Even the BC of the Nosler bullet that was 45% overestimated remains the same today -- in the advertising. So, my conclusion is that it is still buyer beware!

Inaccurate Specifications of Ballistic Coefficients

 

[284winner]

I stumbled across a paper written by Michael Courtney for the U.S. Air Force Academy on the issue of actual measurements of ballistic coefficients not achieving BC advertised by bullet manufacturers. It is a bit dated, 2012, so this may be old news for some. But I thought I would post it anyway. I think we get lulled into thinking we can plug these numbers into our computer and calculate to a tenth of an inch where the bullet impact will be at 300 yards. That may not be so based on this report. There are very significant differences between advertised and actual BC's.

The report dismisses the theory that bullet yaw caused by shooting out of a light sporter barrel is responsible. It also dismisses measurement error. That kind of leaves manufacturing tolerance issues where the bullet shape does not match the intended design, and simple optimistic calculation methods.

Out of curiosity I did a quick average of overestimation error by manufacturer. Here are the results:

MFG (samples) - % Overestimation
Federal (1) - 23.1
Nosler(11) - 17.4
Berger(7) - 12.3
Barnes(3) - 9.6
LC(2) - 7.9
Hornady(2) - 3.9
Speer(1) 1.6

Here is the link if you want to read the details. I did some quick checking of the specifications in this report and what the manufacturers are reporting today on line. Since the report was written in 2012, I thought perhaps some of the manufacturers may have changed their advertised BC's. Doesn't appear to be the case, although I only checked a few. Even the BC of the Nosler bullet that was 45% overestimated remains the same today -- in the advertising. So, my conclusion is that it is still buyer beware!

Inaccurate Specifications of Ballistic Coefficients

Pretty out dated. 2012. Alot has improved since then. At least with Berger. Not surprising tho. Alot of them companies are still way off

 

[John Russell]

I stumbled across a paper written by Michael Courtney for the U.S. Air Force Academy on the issue of actual measurements of ballistic coefficients not achieving BC advertised by bullet manufacturers. It is a bit dated, 2012, so this may be old news for some. But I thought I would post it anyway. I think we get lulled into thinking we can plug these numbers into our computer and calculate to a tenth of an inch where the bullet impact will be at 300 yards. That may not be so based on this report. There are very significant differences between advertised and actual BC's.

The report dismisses the theory that bullet yaw caused by shooting out of a light sporter barrel is responsible. It also dismisses measurement error. That kind of leaves manufacturing tolerance issues where the bullet shape does not match the intended design, and simple optimistic calculation methods.

Out of curiosity I did a quick average of overestimation error by manufacturer. Here are the results:

MFG (samples) - % Overestimation
Federal (1) - 23.1
Nosler(11) - 17.4
Berger(7) - 12.3
Barnes(3) - 9.6
LC(2) - 7.9
Hornady(2) - 3.9
Speer(1) 1.6

Here is the link if you want to read the details. I did some quick checking of the specifications in this report and what the manufacturers are reporting today on line. Since the report was written in 2012, I thought perhaps some of the manufacturers may have changed their advertised BC's. Doesn't appear to be the case, although I only checked a few. Even the BC of the Nosler bullet that was 45% overestimated remains the same today -- in the advertising. So, my conclusion is that it is still buyer beware!

Inaccurate Specifications of Ballistic Coefficients

There is no standard set to test for bullet's BC. Each company uses their own method to establish their BCs and they to not compare to each other - the 224" 53gr V-Max has an advertised BC of 0.291.
The 55gr Sierra BlitzKing has an advertised BC of 0.271 - but the REAL BC of the Sierra is higher than the V-Max - i.e... at the same muzzle velocity, the SBK shoots flatter.

You need to test the bullets - it is not plug and play, and never will be.

 

[RonAKA]

There is no standard set to test for bullet's BC.

Bullet manufacturers should publish muzzle and 100 yard velocities for their bullets. Some 22LR manufacturers put the tested velocity of the ammo as part of their lot number. With the velocity numbers, anyone who cares can calculate their G1 and G7 BC's.

I think it is a bit of a Mexican standoff between manufacturers. Nobody wants to be the first to lower their BC's to realistic values. It is kind of like years ago auto makers would use crankshaft horsepower that nobody could verify

 

[John Russell]

Bullet manufacturers should publish muzzle and 100 yard velocities for their bullets. Some 22LR manufacturers put the tested velocity of the ammo as part of their lot number. With the velocity numbers, anyone who cares can calculate their G1 and G7 BC's.

I think it is a bit of a Mexican standoff between manufacturers. Nobody wants to be the first to lower their BC's to realistic values. It is kind of like years ago auto makers would use crankshaft horsepower that nobody could verify

That is cynical and not true. Each has their own way of testing - Sierra's program is dead on with their bullets and their BCs and THEIR software... The other companies have their own way.

Until there is an agreed method to test, it is not a plot against shooters, and unlike SAAMI, there is no organization to coordinate loading or ballistic data - and there is so much BS to wade through.

Testing at muzzle and 100 yds will do nothing for anyone... at 100 yds, nobody cares!!

The BC at 100 is not the BC at 500 or 1000 - and bullets can start with the same BC and be very different at long range, and G-1 and G-1 are still only approximations... plus there are several other BC "G" drag models - organizing theme s like herding cats.

Nobody is trying to sell you crankshaft horsepower.

 

[RonAKA]

Nobody is trying to sell you crankshaft horsepower.

But if you read the report, the BC's that are advertised are virtually all wrong, and virtually all optimistic. And, from what I can see, the manufacturers are still using the same BC's for the same bullets. Hard not to be cynical...

 

[John Russell]

But if you read the report, the BC's that are advertised are virtually all wrong, and virtually all optimistic. And, from what I can see, the manufacturers are still using the same BC's for the same bullets. Hard not to be cynical...

Michael Courtney wrote an article that was published in VHA a few years ago, and it was rife with technical and procedural errors. He is NOT an expert in BCs.

 

[STOMP442]

Didn't Bryan Litz do the live fire testing for the data in that VHA article? I have read that article numerous times and have the issue somewhere.

 

[John Russell]

Didn't Bryan Litz do the live fire testing for the data in that VHA article? I have read that article numerous times and have the issue somewhere.

No... he did a different article, and found that his results were very different than Michael Courtney's

 

[DocUSMCRetired]

Their is more going on than you think here.

1) Not using optimal twist rates during testing.
2) ICAO vs ASM
3) Not publishing the velocity at which the BC was gathered.

But not all companies publish bad BCs or Marketing BCs. Some are very honest, and will even give you the test rifles Specs. ABM, Berger, AB etc. But its also important to note, some companies are now admitting to using Marketing BCs and not long range shooting BCs on the box.

 

[284winner]

Typically advertised BC doesn't really matter anyway. We all do the range work to fine tune to the exact numbers anyway. When I use my ballistics calculator and input the received BC data, it puts me within .5 minute range on ranges out to 600 yards. BC numbers are more for advertisement and marketing. As Doc stated, twist rate and velocities unknown for those numbers mean alot. I design my own velocity based on accuracy so it's a non issue anyway.

 

[RonAKA]

Michael Courtney wrote an article that was published in VHA a few years ago, and it was rife with technical and procedural errors. He is NOT an expert in BCs.

I can't seem to find a copy of that original test, but I gather around 2008-9 he did a first test. I gather the second test was in part to address some of the issues raised after the first test by Litz and others. Second test appears to have confirmed the first test. You don't have to be a ballistics expert to measure two velocities and calculate BC. Essentially that is all they did. I think Litz and the authors agreed in the end, that measurement error was not an issue.

 

[John Russell]

I can't seem to find a copy of that original test, but I gather around 2008-9 he did a first test. I gather the second test was in part to address some of the issues raised after the first test by Litz and others. Second test appears to have confirmed the first test. You don't have to be a ballistics expert to measure two velocities and calculate BC. Essentially that is all they did. I think Litz and the authors agreed in the end, that measurement error was not an issue.

Well, actually, Litz came up with a "new theory" to explain the differences - Litz said that bullets from light barrels (Courtney) have lower BCs because they leave the muzzle at a 10° angle and wobble to the target, and THAT was Litz's explanation - one of the the dumbest things I have ever heard.

 

[Keith Glasscock]

Believe what you want, but in the end of the day, your intrepid author admitted to using his findings to try to embarrass bullet makers. With all of the arguing and rationalizing that went on aside, ask yourself why he would do that. What was really to gain?

I believe in experience, direct experience. My direct experience tells me that Litz' numbers are very accurate out to 1k yards. If I had to bet my life or reputation on a shot, I'd be using the numbers developed by Bryan Litz.

I've also learned in my journeys how to "read" a bullet and compare its performance to the test specimens fired. That means a new lot of bullets could have a measurably different BC from a previous lot. There are areas of the bullet that have consistent effects on the total drag. Variations there can be corrected for to some extent prior to firing the first shot.

I can only encourage you to read Bryan's works and take bullets into the field to learn for yourself how it works in your backyard.

 

[STOMP442]

Here is a picture of the first paragraph from the article in question. It clearly states they were comparing advertised data to that of Bryan Litz testing. This article came out before any of Bryans books and I found it to be very interesting and informative at the time.

I also made a pdf of the entire article. If anyone wants a copy shoot me a PM and I can email it to you.

 

[RonAKA]

Well, actually, Litz came up with a "new theory" to explain the differences - Litz said that bullets from light barrels (Courtney) have lower BCs because they leave the muzzle at a 10° angle and wobble to the target, and THAT was Litz's explanation - one of the the dumbest things I have ever heard.

I believe the second report effectively dismissed that as a credible answer. They measured BC further out when the yaw should have straightened out and found no difference. And they did high speed photographs and saw no yaw...

 

[RonAKA]

With all of the arguing and rationalizing that went on aside, ask yourself why he would do that. What was really to gain?

I wondered why the US Air Force Academy was testing bullets, many of which were intended for sporting purposes. Then I noticed that virtually everything they tested was .223 or .308 military caliber. I kind of assumed they must shoot those bullets as part of their training and perhaps internal competition. Agree it is kind of strange for the US government to be funding that kind of report... That said, I think their tests are valid.

 

[Keith Glasscock]

I don't disagree that marketing BCs are commonly put out by manufacturers. That is why I use experimentally developed trajectories for my shooting.

In aviation, we use a general rule when it comes to performance. The rule states that interpolation is permissible but extrapolation is not. The reasoning behind that rule and my disregard for low velocity short range estimates are the same. Making assumptions is always hazardous to the truth.

 

[Rtheurer]

I wondered why the US Air Force Academy was testing bullets, many of which were intended for sporting purposes. Then I noticed that virtually everything they tested was .223 or .308 military caliber. I kind of assumed they must shoot those bullets as part of their training and perhaps internal competition. Agree it is kind of strange for the US government to be funding that kind of report... That said, I think their tests are valid.

Or maybe it was paper that they needed to do and that was there topic... Just sayin.

 

[RonAKA]

In aviation, we use a general rule when it comes to performance. The rule states that interpolation is permissible but extrapolation is not.

Tell that one to the climate change "scientists"!