Home Forums Hunting & Shooting Long Range Hunting Ballistic Coefficient discussion

I know that some bc measurements are more accurate than others. Looking at some of Bryan Litz's work and Sierra's numbers it would seem that bc changes as velocity changes.

example from for Lapua 155 Scenar from Applied Ballistics

fps / BCG1
1500 / .411
2000 / .458
2500 / .473
3000 / .493
Average/.459

Sierra Also lists bc's for different velocities as found on their website.

Questions:
-Do most manufacurers just advertise the bc for the higher velocity?

-Should use the average bc within the velocity range from muzzle to target when calculating or comparing drop/drift?

Numbers from a guy like Litz will usually be more accurate'er than the manufacturer.

Either way, numbers are just something to use to get you on paper. Only you can determine how great a bullet is or isn't.



Dave

^^^ BC's are, from manufacturer's, are a comparative value, this bullet higher/lower than that one.

With the LabRadar, which gives velocities at several user determined distances, you can calculate the actual BC for your elevation and environmental conditions. From actual bullet drops.

I use Litz's BC's to get in the ball park, they are actually pretty close.

He'll no doubt be calling you when he's ready to write his next book.

In general Doppler radar is the gold standard for external ballistics as prior to LabRadar the radar units would give you position vs. time for the bullet from muzzle until the transonic and beyond. I may be wrong but I think LabRadar units only give you information for about 200 yards.

To calculate the ballistics coefficient accurately you need to get the data closer to the transonic region when the bullet is dropping more more.

I have built a ballistics solver that matched up with the commonly held accurate solvers that would take radar drag curves or BC's as I was doing testing on a range that had a commercial doppler radar system. As a measure of how close Bryan's published BC's were I compared the results on 5 Lapua scenars, these were the only bullets that I had both radar drag curves and Bryan's BC's. The ballistic solutions with the BC and the gold standard the radar drag curves, were well under .25 MOA along the entire path. That is pretty good evidence that Bryan's BC's are very good for modeling trajectories.

I have no idea where Litz does his testing, at sea level or 6000 feet, or any varying environmental conditions, no idea if the twist rate of his barrel is optimized for the bullet or not.

The tools are available for the hobbyist today to model BC's and apply that to a drop chart. This is only done by actual field testing and known velocities.

I suppose this doesn't make any real difference to cowboy action shooting or any less scientific endeavors.

Exactly. So how is it that you are able to rationally comment on the relative accuracy of his findings?

The result of field testing concurs very close to his findings.

Field testing will reveal any anomalies that my conditions have as compared to his.

So, if I use a G7 of 0.324 for a 208gr A-max (this is a Litz BC) and plug all pertinent data into a ballistic program and find that my result is ,lets say, 2 moa different in drop than his then the 'effective BC' in my circumstance is different. If I know the difference then I can account for it.

This is but one of the items used to build an accurate drop chart.

Another example is a 200gr Accubond has an advertised G1 of 0.588 and a G7 of 0.273. The testing I have done indicates a G7 of 0.268. This is most likely due to a lower velocity, slower twist rate than normal (1:11), elevation and atmospheric conditions.

Commenting on relative accuracy of Litz's BC's was done through field testing.

You can do that too, the 'kicker' is you need accurate velocity readings, the rest is math and working the program.

As always, trust but verify.

If you don't know the conditions under which he conducted his tests, you have no idea how accurate his results are, and no basis upon which to comment on his accuracy.

That's correct , I do not know what conditions he tested under.

I do know that his BC's are more accurate than some manufacturers published figures.

I do know his figures are very close to my testing and ,as I said, use his figures to test reality in the field.

Now if Litz comes up with a BC of 0.273 and my field testing reveals 0.268, this does not mean my findings are better than his. It just means that I use the coefficient of 0.268 to build an accurate drop chart (for my conditions), that's all.

When I plug all the pertinent data into a Ballistic calculator (I have already verified the correct factor on my scope) and it tells me to come up 25moa to center at 1000 yards and time and again I need 26.5moa, this tells me the variable is the bullet's BC (I know my muzzle velocity and up to user defined distances), I then adjust the BC to reflect the actual come up or just ignore it and use 26.5 moa as the come up for a 1000 yard shot. This only works for one distance, better to plug in the new BC and test at varying distances to how ever far you want to hit.

So, anyone can comment on Litz's BC's. I use his as a default but also field test.

I am in no way challenging Litz's numbers as they are as close as they come.

I don't think anyone is attacking Litz' numbers. BC values will change from rifle to rifle. Individual rifling dimensions and the resulting engraving on the bullet will affect BC, so when a bullet manufacturer or third-party ballistician publish numbers, they are 100% applicable only so far as the testing/calculation techniques and test rifles used. Litz' testing uses the most advanced methodology that I'm aware of, which is why his numbers are the most universally applicable. But the actual BC value from your specific rifle may differ slightly.

The only trouble with determining the BC difference, is getting accurate and precise measurements on velocities and bullet drop at range. Often when a guy thinks his bullet's effective BC varies from what is published, what's really going on is that his chronograph has a 1% error resolution, or his rifle isn't accurate enough to determine drops with enough precision to identify any small difference in BC.

what's really going on is that his chronograph has a 1% error resolution


^^^ very true, optical chronographs will vary from one range trip to another as set up is critical and changing light conditions play with accuracy, along with the built in up to 1% error.

The Labradar claims 0.1% error and that's what I go with. Accurate velocity readings are the grail.

I wonder how a guy can tell if the 0.1% error rating is accurate or not. It's quite a new product, so user technique subtleties may not be apparent yet. The Shooting Chrony claims less than 0.5% error, but time and experience has shown that to not always be the case

A shooting chrony gives me an ES of ~30 fps over the last 25 years I've had it. Sometimes less sometimes more, but never settled down.

Some of these were very good loads according to the target, holding an MOA to 1000 yards.

Now my very good loads have ES's <10fps and I see it on the targets.

Accurate velocities made it possible to see the effect of changes I've done to lower ES, made the Quickload program work a lot better, which again shrunk groups.

Those 1/2 moa groups at a 100 yards that never stood up at long distance were ferreted out as to having unacceptable ES's that weren't seen on the target at 100.

So, is it 0.1%, I don't know but Quickload works as it should , Ballistic calculators work as they should, and if not you can find out why not.

Solving any equation that requires a velocity seems to work out now. The unit sits beside the bench and every shot is recorded which begins to build a good statistical record.

Back to the calculation of BC, correct velocity is the key for any calculations.

So, in short, I didn't just believe it, I worked it, as science is not faith based.

I'm glad it's all working out for you. Having said that, things usually work out for me pretty darn well using a Pro Chrono.

Precise velocities aren't the same as accurate velocities. Repeatable readings don't necessarily mean correct readings, which is the whole premise behind correctly calculating BC values. You'll still get incorrect BC values even is you have an ES of 0 over 50 shots, if all of those velocity readings are 100 fps too fast. The factors all working out as they should doesn't mean the velocity readings are correct, it just means that everything lined up.

Precise velocities aren't the same as accurate velocities

^^^ I don't what your after on that one.

The velocities that I get with the Labradar jive with known BC's when calculating a drop chart, due to the ease of recording every shot , a velocity average can be determined over a large sample size.

With this confidence in velocity other changes are much easier to see.

So if I have an ES of 20fps, over 100 shots I will average them , the velocity could be 2952fps. This is what I use to calculate BC's for external ballistics and Quickload for internal ballistics.

The lower the ES the better it will be for calculating either.

While not perfect it is much better than what has gone before.

If the math doesn't work then suspect inaccurate/precise velocity readings.

Its the foundation.

To actually address the questions asked...

Manufacturers advertise the highest BC number.

But some manufacturer provide 2 different types of BC numbers for a given bullet.

One is called g1 and the other is called g7... they are equivalent but different BC scales. A higher value is the sleeker bullet using either scale.

So for the most accurate results, when using the g1 scale, select g1 in your ballistics program, and plug in the multiple BC/velocity numbers into the program.

When using g7 numbers, after selecting g7 in the program, you can just use the single g7 BC number.

That way the calculated results should be similar.

Axtell, My hat's off to you! Your patience seems endless!

I still have some patience left, But now conserve what little is left for those who truly deserve it.

Y'all just need to buy some 165 grn core locks for a 300 ratherby. They are flat to 800yards, is the word. 🙄👌. And tasco 3x9 they rock too.

Smokes been upset sence this whole transgender stuff came up give him some slack.

I can totally understand that environmental conditions, twist, etc can change the bc. But it would be nice if there were a industry standard for measuring/ advertising bc's. That way we could make a direct comparison from manufacturer to manufacturer.

That's not patience. Axtell went from implying that his BC calculations were more accurate than Litz's to admitting that they were not.

The fact that it took him several posts to backpedal is not patience, it's arrogance.

Axtell is also the guy who touts the fact that he weighs his powder charges using a jeweler's scale to the nearest 0.02 grain, and claims that this makes a difference.

I have no patience for such claims.

Fred's orientation notwithstanding.

Rabbit trail maybe, but all this talk about minutia, % of difference here and there, but I never hear anyone talk about how the rifling deforming the bullets smooth slippery surface changes BC. Seems like that'd change everything.

Jordan pointed that out a few posts back.

Smokepole

You are reading this initial post incorrectly. You are presuming that you can take a listed BC plunk it into a ballistic program and get 'advertised results'.

The above statement clearly states that I use Litz's BC's, as they are the best available, as there is no bias to marketing by a manufacturer.

Now using Litz's BC's do get you in the ballpark, but sometimes require fine tuning (for your particular circumstance)as laid out in subsequent posts.

There is no back peddling on my part. Only time spent in an effort to understanding. You seem to have your mind made up, so I guess it was a waste of time, my bad.

You have had a hard on for me since I questioned your buddy H-22 about his Ruger blowing up. The line of questioning was hard but sometimes that is what is necessary to uncover the sequence of events that caused the incident.

Weighing powder: consistency is the grail in producing good ammunition, weighing powder to the nearest 0.02 of a gr takes no more time than weighing to the nearest 0.1gr on a balance beam scale, so why not. Further, measuring seating depth or COL is more accurate with a vernier than a yard stick. Most would grasp this idea.

The arrogance smoke screen is just one that tells me that you do not understand these basic concepts......therefore reject them, as you have no ammo for debate.

Axtell,



What kind of powder do you use and how much does one granual weigh?

With all these measurement discussions, there is a level of resolution within which a material difference in results can be observed. Remember Sig Dig's? Significant digits- greater resolution adds no greater significance to the data. This is to say that measuring cartridge BTO length to within 0.0001" has no observable impact on results, just as measuring powder charge to within 1 granule has none, nor does calculating BC values to 0.0001.

I'm presuming nothing, just reading what you wrote. When you say someone else's numbers are "pretty close" you're saying the numbers are good, but could be better.

In other words, you're saying Litz's numbers are close but not right on.

The only way you can know that is if you have better numbers, and that's what your statement implies.

Which is nonsense.

And that BS you were directing at Huntsman has nothing to do with it. I just think you're FOS.

H-4350, Varget, H4895 and H-1000 weigh ~0.02 of a grain per kernal. I mostly use these powders. The finer/denser extruded powders like VV N-550, to a lesser extent RL-17 are harder to get +/- one kernel.

My scale only resolves to 0.02gr so any weights I get are within this parameter.

It took me some time to develop a technique that gave accurate results in a timely manner.

BC's will vary somewhat due to as stated previously twist rate, environmentals and in addition the degree of 'damage' the bullet gets as it enters the rifling all play a part.

There are no better numbers ......just numbers that jive with reality of bullet drop.

I won't go into the effects of refraction, probably a waste of time in this conversation.

Depending on your shooting discipline, whether it is hunting deer at near ranges, varmints at long range or 1000 yard competition, will dictate the level performance required for success.

Its better to have a high level of performance and not need it than the other way around.

I agree, there is a point where effort and reward are immeasurable.

But, do not abandon good practice, try to keep things tight, the reward is consistency.

With the tools available today there is less effort and greater reward than has been previously known.

I see this in group sizes shrinking and the probability of a hit increasing.

Yes, that much is clear and it's been stated by a few different posters already so there's no need to repeat the obvious.

It doesn't lend any credence to your posts, all it does is show how ridiculous it was for you to say that someone else's numbers were "pretty close."

A bullet's BC is independent of atmospherics, the atmospherics are entered in a ballistics solver to obtain density of air and speed of sound not to change the BC of a bullet. Please read this book if you are in doubt about the BC's independence of atmospheric conditions.

I am not saying that atmospheric conditions do not change the trajectory because it does because the denser the air is the greater the drag is, assuming both bullets are the same and have equal speeds.

^^^

When punching info into the Ballistic program, all known parameters, the variables are mainly elevation and environmentals.

So, in the program to get an accurate drop prediction what changes..........its the effective BC of the bullet.

To say a BC of a bullet is x.xxx is most likely a reference to a standard.

Does it make a lot of difference , not likely , but it gives an understanding of what is happening.

Or , one could defend a position with walls made of words that include arrogance, BS, ridiculous, the obvious which probably is delivered with a huge eye roll.

I'm pretty sure you deliver all of that with a straight face.

Pretty much, trying to keep from slipping into Alaska trailer park ghetto talk. Have yourself a good day and shoot straight.

Had a discussion with one of the Nation's top PRS shooters about this very subject. He's been weighing charges to the granule and has seen SD's for strings of 30 rounds reduced to 8

OK, but can any improvement from this be reliably resolved on target?

Which brick do you take out of a wall that allows the whole structure fall apart ?

I will not knowingly degrade my standards to the Lee powder dipper method, which btw are pretty good for hunting grade ammo inside 200 or so yards.

Not exactly. The only thing that the ballistic calculator is figuring out WRT environmentals, is how dense is the air that the bullet is flying through, or in other words how much aerodynamic drag is the bullet experiencing in flight. Elevation is irrelevant if you know the pressure and temperature, or just the density, of the air at your firing position.

The BC is a measure of how aerodynamic a given bullet is compared to a standardized bullet. Environmental conditions don't change that, since they apply equally to all bullets, they simply increase the level of resistance that the bullet has to overcome.

The BC is simply expressed by form factor, or bullet shape, and SD. Rifling engraving changes the shape, and therefore changes the form factor. Environmental factors don't alter the BC of a bullet directly, but I see what you're saying that they indirectly affect the bullet's flight characteristics.

While not charged with a Lee Dipper, these loads were all thrown with a Quick Measure, not trickled, and not weighed individually. These groups won't win any BR records, but I doubt that observed results would improve noticeably by increasing the precision of my powder charging technique.

Yes it can, except most people don't have the ability, equipment, or desire, to do so.

Here's 2.3" 1000 yard BR target:

It really comes down to accuracy requirements vs. time/volume of ammo production. For plinking, throwing a good load with my QM can get right around 0.5MOA accuracy or better, as shown in the group pics above. That is with a variety of barrels, ranging from factory to top end. But if I'm going to a LR competition, I'll take the time to weigh each charge with scrutiny. Same with the BR game, the accuracy requirements are higher, and the need to produce ammo in high volumes is lower.

Interestingly, the chrono results Rick quoted above show more meaningful SD values than most. When we start to get 30-50+ shots included in an SD calculation, that increases the confidence in the sample representing the load's performance. I think most guys who claim tiny SD's based on a few shots over the chrono, would be disappointed if they kept shooting until they had 30 rounds measured and factored into the SD value.

While I agree 1000 yard benchrest would be the ideal proving ground, I can't agree what you've shown constitutes proof of concept. That would need a few blind tests.

All true. My first sentence was to address the notion that it can't be seen on a target. Most don't pursue the ultimate results for whatever reason. I dump powder all the time with a measure for various things, but I do weigh every charge for stuff that matters, like 1000 yard Benchrest. Anyone can shoot a small group, but attention to details ensures a repeat performance.

BTW, 1 grain of Varget does weigh .02 grains....

I've shot 1K BR long enough to prove it on paper.....

Not knowing which ammo you were shooting for a given group in a series of say ten groups, with perturbations of one kernel of powder vs. dead nuts?

How about you prove it doesn't matter......

Have you got the ability and equipment?



62 pounds with an 8" forend and 3" butt makes for a pretty good test vehicle....

I won't be weighing to the 1/100 grain, believe me

I'm an Audette developer dude and weigh on an RCBS 750 to the .1 grain if I can keep it zeroed and calibrated


The Audette seems to produce the same results or results that are just as good on the target......



800 yards...




1370 yards....




1610 yards...




1825 yards...

I thought you might go that way with the discussion, but it doesn't really address the question. Make no mistake, I'm not of the belief that since I can't do it then you can't either. I know I don't have the skill and equipment to resolve such a fine detail. To prove it does/doesn't matter requires the equipment and skill you possess. My sticking point is you'd need to run a several blind tests.

Rick,

I agree that it's not always necessary to weigh charges with the utmost scrutiny to get pretty darn good results on LR targets. Here are a few more of mine. These are also all thrown loads. Notice the vertical on the longer targets...

I knew I was going there too......

We agree more than we disagree, but when I'm loading for a match, it doesn't take any longer to weigh to the kernel than not. I use a Sartourios that weighs to the hundredth, but I don't fret over a couple either way.

1K BR is all about the details, so stacking tolerances will not bode well in the end. There may be more than one thing I do that may or may not make a difference, but the expense of testing every one is too costly in a $600 barrel, but costs nothing to do, except a little time.

I've set enough club, state, and world records to prove what I do is not for naught....

1K 10 shot groups can be more telling in your loads....

The other poster did fret over them though, and in a less exacting discipline IIRC. That's what got me started.

I appreciate a good conversation, so thanks.

aalf,

There is no question that 10-shot groups are absolutely more telling than 2,3, or even 5. Having said that, nobody is as picky as the BR guys when it comes to absolute accuracy, and groups that would probably place you in last place, would likely put a big grin on the face of most other shooters, even competitors in other disciplines. You don't need to be able to put 10 shots into groups in the 0.3's to hit a 1.5 MOA steel plate or a deer at 700 yards

For competing, each cartridge should get the utmost attention, but for plinking, mass-produced ammo that shoots 0.5 or better is perfect, at least IMHO.

Excellent shooting, BTW!

Yea, we didn't get too side tracked....

And to summarize (repeat?), it still takes ability, equipment, and desire.....

Usually the definition anal...thanks.

If anyone is interested in a peek inside Litz' mind when it comes to analyzing accuracy and precision of chronograph's you can read here;
http://appliedballisticsllc.com/Articles/ChronographChapter.pdf

I've also read his experiences with the LabRadar and I'll poke around and edit in a link if I can find it again.



Inherent in this statement is an assumption that your LabRadar unit is more accurate than what Litz is using. They claim 0.1% accuracy which makes for 3fps error on a 3000fps capture. Litz' Oehler was similar for precision (though I can't comment on accuracy because his 12ft Oehler was his comparison standard).

Axtell, I'm curious how you conduct your "field testing" to measure your BC's and plot out your drag curves. Is your "field testing" based on your LabRadar? Or are you using an Infinition or other doppler radar system from work? Because here's the thing; the folks at LabRadar told me the best I can hope for in capturing velocities downrange is about 150 yards with a 30 cal if I'm lucky (progressively less as the caliber shrinks). Also they told me I can't put the unit further down range like Bartholome and Litz do with the Oehler on occasion to stretch out the drag curve. They don't work like that. Does that mean you're calculating your BC's using 150yard data and extrapolating beyond to build your drag curves and get your G7 and drop values? Or are you taking drop data and backing it into your computer to give you a BC?

Help me understand as I'm simple and confused.

RCarmuglia,
It's interesting that your friend cited a SD of 8 for a 30 shot string. A long time ago, Bob Jensen who loaded the ammo for the 92 Palma matches cited a sigma 7 as the holy grail for 600 yard loads in my sport (Highpower Rifle). (I'd have to check what N was attached to that). What's interesting is he dumped powder for the 92 Palma Ammo. He shared that he got his sigma 7 through means other than granule accurate powder charging. I think he attributed testing primer lots by shooting primer powered bb's out of a special rig over a chrono to test their consistency and force (he said softer was better). Alan Warner feels otherwise on powder charges. He told me that kernel counting powder charges was the way to consistent elevations at 1K. I think he was trying to rationalize his purchase of his Prometheus. I have a Gen1 and it doesn't make me hold elevation like the Tompkins clan.

Here's Litz' early impressions of the LabRadar;
http://forum.accurateshooter.com/threads/preliminary-labradar-testing.3871199/

What's also worth reading are posts 7 thru 10 of this thread, where he essentially voices what I did above along with a few other things that I didn't think of such as trajectory angle skewing the calculations.

He and 2 others are using a $550 scale that measures to the 1/100 grain. Not sure of the name. They also use a special powder trickler.

Does that mean you're calculating your BC's using 150yard data and extrapolating beyond to build your drag curves and get your G7 and drop values? Or are you taking drop data and backing it into your computer to give you a BC?


Pretty much that is it.

Taking velocities at face value from the LR I've found that the BC's advertised do not always jive with the ballistic calculator. This assumes correct inputs for atmospheric conditions as best as possible (the Vortex calculator is good for that when you know your position).

Testing reveals that some bullets do not actually fall to the POA as predicted in the calculator (tall test verifies scope correction factor).

Ultimately I take the data garnered in the field and 'back' it into the program.

Many times using Litz's BC's things work out as come ups are as predicted.

I think what is skewing my results on occasion, are a combination of, velocity too slow, rate of twist not optimized and some rifles damaging the bullet a bit as it enters the rifling.

With the Labradar an up date to version 1.1.3 solved the 22 caliber issue.

I'm pretty sure one consideration was the need to produce a quarter million units. That's the figure I recall from the article in Handloader magazine.

In some forum I read where Litz is now using the new Oehler system 88. From what I could gather the 88 can measure time of flight to within a millisecond at ranges over 1000 yards, uses GPS, radio and acoustic targets and is battery powered. Given the quality of Oehler stuff and the skill of Litz I expect we'll see even more accurate data in his next book.

[bleep] A Aalf that is some very nice shooting brother and I don't compliment much.

It is indeed hard for me to wrap my small brain around how someone can't realize/understand/agree that a single grain of powder can, will and does make a difference in combustion energies produced.

If I was that anal or desired such beyond what I get on my gear you can bet your fart maker that I would have a scale that would do exactly such.

http://www.googleadservices.com/pag...cO1loPPAhXBNz4KHWadCwQQwg8IIQ&adurl=


The only book you'll ever need!

Has anyone considered...........ah, who am I kidding.


Carry on.

Haha makes me wonder how I've a garage/shop full of bone.... Puzzys...

They key word in hunting, is "hunt"...... But that's simply not cool. A "hunter" needs to shoot rimfires and everything else at dumb range, cause there's nothing else to do.... Poor dumbphuques.... Don't "wonder" when a wife strays, or a sibling eats a boolit.... Hint, re hint, re hint +++ P

Oooooops the magical word, "hunt".....

Mebee the do nothing crowd should say, long range "shooting"?????

"There are lies, damned lies, and then Statistics!"

Winston Churchill

There are those that do, and those that dream....

And then there are the west coast libs that live happily amongst the top ten gayest population whilst spouting judgement from their child chit filled holes, voted democrat the last seven elections and can't hit a can past 200.. Carry on

I vote R am a deplorable azz and shoot the chit out of cans so hold your tongue 9. We ain't all bad.

http://youtu.be/Q8Ax9W2H54A

. Ps 1000 yards

And your drinking one of my favorites, you pass!! But I do prefer bottles in that flavor if your ever buying.

Noted if the opportunity ever arises bottles it is.

Its the long range "hunting" forum, true. But its where we talk about precision LR shooting as well, like this thread.


Only one talking about hunting is you, for some reason.

I'd say if someone wants to be a long range hunter, he ought to do a lot of long range shooting first. Unless you're hunting beer cans like Fred. Fred, did you get an exit wound?

She was standing on the lid. Lol if it helps I shoot sticks, rocks, paint dots ect.

That's impressive penetration, must've been a Barnes.

I'm not seeing evidence of the "4 razor sharp petals cutting like a buzzsaw" thru that aluminum.

Coors - the .270 of beers . . . I drank a few when I was at Mines.

The 4 razor petals only show on PBR cans , thicker steel, I mean tin, I mean aluminum but anyway its thicker see.

LOL.