Over the years it has always annoyed me that the .323/8mm bulets always are credited with so low BC's.
Look at this link from Nosler,
http://www.nosler.com/index.php?p=11&b=5&s=3

A .30 180 grs bullet with a SD of .271 have a BC of .507, but the
.323 bullet at 200 grs with a SD of .279 only has a BC of .379!!
And then the .338 bullet at 200 grs with an SD of only.250, exeeds the .323 with a BC of .414!!

This does not make sence!!! Same SD should give about equal BC, and that fits the other calibers!

The same differences can be found also in the Barnes manual as well as other manuals! Is this some stupid discrimination of the 8mm, or what the heck?????

Bent

Sd is a function of dia/weight while BC has everything to do with shape.

It's entirely possible to make 8mm bullets with a BC as high as 6, or 7, or 8. Place an order for a couple million and they will make them for you.

Ray

Is BC just a computer calculation? Or is it empirical evidence compiled through testing? One reason I ask is that it seems the initial velocities may also have something to do with BC as well. Someone please set me straight on this.

How many different 8mm bullets are there on the market? One of the reasons why the 8mm Mag never really caught on was because bullet manufacturers didn't pump out 8mm bullets like .270, ,280, .30, .338 or .35. If they did, you wouldn't have this problem.

I totally agree, I believe the BC figures for 8mm figures on Noslers site are false.

The .323 200 grn AB should have a higher BC than the .338 200 grn AB. It should be somewhere between the .308 200 and the .338 200.

Reloader

There's definitely a problem here. Just look at Sierra's and Hornady's 8mm offerings.

The .323 Hornady 195 grn flat base has a BC of .410 and the .338 200 grn FB has a BC of .361 which is how it should be.

Sierra makes a 200 MK for the 8mm that has a .520 BC

Nosler flubbed the BC figures on the 8mm AB or exagerated the .338 AB

Only real field testing will give you the actual BCs but, I'd be willing to bet the 8mm AB would be higher than the .338 AB in equal weights.

Reloader

quote:

Originally posted by Wink:
Is BC just a computer calculation? Or is it empirical evidence compiled through testing? One reason I ask is that it seems the initial velocities may also have something to do with BC as well. Someone please set me straight on this.

For the most part, BC values are calculations. It would be cost-prohibitive for bullet manufacturers to determine the BC of their bullets from actual field testing. However, there are some that have been determined by actual firing. But, the calculations are usually close enough. You can do it for yourself with a couple of chronographs. And yes, velocity is a big factor.

BC values are like velocities. Nobody believes them. Even after you shoot thru two chronographs there are shooters who still will not believe the numbers. The same skepticism applies to wind deflection. Exterior ballistics is basic laws of physics. You can't change or even bend them.

This site offers a helpful discussion of this topic:

Ballistic Coefficient

quote:

Originally posted by Reloader:
I totally agree, I believe the BC figures for 8mm figures on Noslers site are false.

The .323 200 grn AB should have a higher BC than the .338 200 grn AB. It should be somewhere between the .308 200 and the .338 200.

Reloader

I agree. The .323 cal 200 grs Accubond is a pretty sleek bullet - comparable in both length and shape to a .308 cal 180 grs AB. I have wondered myself how Nosler got those numbers??
- mike

1. because we have no real interest in the 8mm caliber in this country.

2. appearances can be deceiving...remember the "swoopy" 1968 Corvette Stingray? It was only 4% more aerodynamic in forward gears than in reverse.
Cd (coefficient of drag) is a better number to work off of. It compares the frontal area to a flat surface of the same square footage. BC just adds the shape of the rear end to deal with the drag caused by laminar airflow from from to rear. As the air passes over the projectile the ease with which the airflow re-establishes it's integration into the atmosphere aids in stability and flight. It's why trimming 1/8" off the rear spoiler of one brand of NASCAR competitors cars can move a car from first to worst and vice versa.

regars,

Rich
DRSS

Thanks to reloader and mho for actually reading my post and understanding my question.

And also thanks to Rich for a honest answer in his No.1 statement!

For those who think i do not understand SD and BC, I can only say - I do.
And that is why I ask this question. When two(close in caliber) identical shaped bullets with identical SD vary so much in BC, something is way out in the cornfields.
It has bugged me over the years, and this thing is present in almost every bulletmakers manual in America. On the Nosler link, you will see the same with the other bullet-types. But I really do not see how they would benefit from badmouthing their own product?

You can try these 338 Lap Mag bullets with a BC of 0.94.



Mark

It is very strange, when you compare the numbers from Nosler's website for their AccuBond bullets:

.308 cal, 180 grs, B.C. .507, S.D. .271
.323 cal, 200 grs, B.C. .379, S.D. .274
.338 cal, 200 grs, B.C. .414, S.D. .250
.338 cal, 225 grs, B.C. .550, S.D. .281

Why this dip in BC for the .323 cal bullet when compared to bullets of similar sectional density?? It is certainly not obvious when you inspect the .323 cal 200 grs AB, it looks just as sleek and aerodynamic as any other AB.

Is this a conspiracy against us 8mm shooters??

- mike

Exactely! And you will see the same difference in both the the Ball.Tip and the Partitions, and it is the same in all my older Nosler Manuals, as well as the Barnes manual.

quote:

Originally posted by MarkH:
You can try these 338 Lap Mag bullets with a BC of 0.94.



Mark

Jupp, I could try them, but just how did you think this was in any way related to my question?

quote:

Originally posted by MarkH:
You can try these 338 Lap Mag bullets with a BC of 0.94.



Mark

O'k, send me a 1000 of them, and I will report back with the result's of my testing!

quote:

Originally posted by Bent Fossdal:
...It has bugged me over the years, and this thing is present in almost every bulletmakers manual in America. ...

Hey Bent, From my perspective, BC is simply an Estimate.

It doesn't matter which Model is used to calculate it, if the old Charts in P.O. Ackley's Handbook For Shooters & Reloaders is used, or if the Bullets are fired and the Velocity change noted or the actual Drop Charted(which is the best of the lot).

1. When picking a Mathmatical Model to use, it seems each manufacturer went out of their way to select different ones. The Method they picked is listed in the older Bullet Manuals and normally a reason listed about why they selected the one they did.

2. The Chart in Mr. Ackleys book works as well as any of the Math Models. Try it some time on a few Bullets and then look up what the manufacturers "think" it is. Lets say they think it is .350BC, your Chart value will mormally be from .300<->.400BC which is as accurate as their value.

3. You can measure the Velocity Loss and Mr. Oehler has a specific Model Chronograph, with two large triangular sonic screens, which can be set up to measure the same exact Bullet as it makes the trip down range. This set-up is relatively quick to set up and I believe comes with 100yds of cable. But even if it is shorter, it would give an excellent estimate, because the same Bullet is measured twice using the same Timer.

4. The best Method seems to be actually measuring the drop over a known distance. This requires a Survey to establish the actual height above Sea Level between two points and the Target Centers need to be at the same height. Then shoot a series of shots and measure the Drop from Target Center.
---

But, there are other problems as well. Changes in height from the Test Poit when actually Hunting, changing Environmental Conditions, changes in the actual Bullet Shape from being made in multiple Dies and then the also changing Bore Condition from shot to shot. All of these things cause the Bullets to fly slightly different from shot-to-shot.

So, that is why I look at BC as only an "Estimate" irregardless of the Method used to determine it. When a person actually understands how these parameters change, it makes you stop and wonder how we ever make consistent long distance shots as easily as we do.
---

And NO, BC is not all about the Base. Rather than argue the Point, I'll just reference the Ackley Charts and people can see it for themselves. Yes, the Base has some effect, but not to the "Point" of negating the overall shape, including the Tip and Profile. Just doesn't work that way.

Good Hunting and clean 1-shot Kills.

I hear you, Hot-Core, and I know how it works, and how the BC is merely a guesstimate.

What is bugging me is that is seems they are using a different formula for their 8mm bullets. If you look at the link from Nosler, there is no way they could have used the same formula on the 8mm.200 grs and the .338 200 grainer.

See?

This is an excellent question! I recall that the 200-grain 8mm Partition bullet was given a higher B.C. than that! (.426 in their reloading #5 manual!!) But I just looked on-line, and it has been dropped to .350.

Is it possible that Nosler has revised their B.C. data overall? Or is there something about the .323" bore size that is just inferior? I doubt it! The Germans wouldn't design a sub-standard cartridge!

quote:

Originally posted by Reloader:
I totally agree, I believe the BC figures for 8mm figures on Noslers site are false.
Reloader

OR, the B.C.'s for the other calibers are optimistic!

The B.C. of most projectiles varies with the velocity. So any ONE B.C. ascribed to any bullet is only valid at one particular velocity, and it changes as the bullet decelerates....

Intresting discussion. These things called B.C. and S.D. serve absolutely no good purpose other than to create discussion. The fact that shape and weight do different things is pretty well known. But to what degree is necessary is never discussed, only how much can we get.

Can someone tell me the practial difference in bullet's of equal cal and different B.C. when fired at say, 300yds? I find that shooting 129gr bullet's out of one of my rifles put's me at little disadvantage when shooting at paper at 400yds as compared to the 140gr match kings I'm trying now. As I understand it, if you have the twist to stabilize the bullet your using then the only thing left is to keep it supersonic.

Which brings up the question of how far do you need to keep it there? Well all we seem to know for sure is the higher B.C. will keep it there for some distence determined by the muzzle velocity.

Would an .323 bullet @ 200grs and BC of .379 be anyless effective than a ,338 bullet @ 200grs and a BC of.414? And if so, how far must the bullet's travel for the .338 bullet to realize it's balistic advantage?

Maybe I'm missing something here!

Bent

You said that no one was reading your initial question and answering it. As I remember, the gist of it was this:

quote:

This does not make sence!!! Same SD should give about equal BC, and that fits the other calibers!

I think all of us tried to answer by stating that BC and SD were NOT the same thing and were not comparable from bullet to bullet.

If I were you and I felt that bullet manufacturers were misrepresenting the BC or SD values of their bullets I would either call them and take it up with them directly or I would use somebody elses bullets. But before you make that call, make sure you really do understand the difference between SD and BC. JMHO

Ray

quote:

Originally posted by Bent Fossdal:
...What is bugging me is that is seems they are using a different formula for their 8mm bullets. If you look at the link from Nosler, there is no way they could have used the same formula on the 8mm.200 grs and the .338 200 grainer.

See?

Hey Bent, I know exactly what you mean.

Two excellent comments here:

quote:

Originally posted by Reloader:
I totally agree, I believe the BC figures for 8mm figures on Noslers site are false.

quote:

Originally posted by El Deguello:
OR, the B.C.'s for the other calibers are optimistic!

I have thought for many years it is primarily driven by the Marketing Groups of each Bullet Manufacturer.

When the Plastic Tipped Bullets came out, it really seems to have gotten much worse. But the desire to have the sleekest Bullet Design by the average Hunter or Shooter sure sold a lot of "Higher Profit" Bullets(to me too ). And fortunately, most all of them were accurate and held together fairly well.

Anyone who ever goes out and actually shoots their Bullets to create their own Drop Chart soon realizes how inconsistent with reality the BC values in the various Manuals happen to be. Barnes got caught-up in the "who makes the sleekest" and has realized it is better to list BCs closer to reality. They are changing them as quickly as they can.

It is easy enough to just set Bullets side by side and see which ones will fly the flattest. No Magic is required. If one Bullet looks a bit sleeker than the next one, it is. But..., the actual differences in Flight Paths is often lost in the Grouping ability at distance.

Few folks believe a good old RN Bullet is useful beyond 200-300yds, only because they never actually tried them at 400-500yds.

Best of luck to all you folks.

quote:

Originally posted by Cheechako:
Bent

You said that no one was reading your initial question and answering it. As I remember, the gist of it was this:

quote:

This does not make sence!!! Same SD should give about equal BC, and that fits the other calibers!

I think all of us tried to answer by stating that BC and SD were NOT the same thing and were not comparable from bullet to bullet.

Well, Ray....I can see how this confused you, but
I was speaking out of the Noslers bullet-board, was I not?
What I should have said was that if two bullets of different caliber have the same shape and SD, they should be proportional in dimensions and therfore pretty simmilar in BC(although sligthly raising as the bullets gets heavier) - which the rest of the bulletboard shows - so I thought my meaning was obvious.
If you care to look;
http://www.nosler.com/index.php?p=11&b=5&s=3
Compare the .30 180 grs with a SD of .271, which gives a BC of .507, and the .338 225 grs with a SD of .281, which gives a BC of .550. This fits, because of heavier bulletweight and slightly higher SD, therfore somewhat higher BC.
But can You then explain to me why the .323 200 grs with a SD of .274 - slightly more than the .30/180grs and slightly heavier - have only a BC of .379???

I am well avare that bullet shape makes the BC, and can differ a lot even if the SD are equal.

Scudrunner,
If you want to try those long .338LM bullets you need a 1:7" twist barrel. They do not work in anything else.

Hot dang, Gerard, how about MY question?

There are several ways of measuring BC. The easiest perhaps is using a couple of chronographs. One at muzzle and the other at say one hundred yards. I suspect that this is the method used most often to measure ballistic co-efficient.

After a lot of data is calculated an engineer could come up with a formula that would match the test results and BC could be calulated based upon shape and denisty etc. Then a bullet manufacture could design a high BC bullet based upon the formula.

BTW: I have read that Ballistic Coefficient varies with velocity. So a guy could load the bullet to different velocities and remeasure.

If a person doesn't have two chronographs the a relative BC could be measured by sighting in say a certain .30 cal 200 grain bullet at say 2700 fps. The take a 8 mm certain grain bullet at 2700 fps. Sight the two loads dead on at 100 yards.
If everything else is the same such as the height of the scope above the bore, shoot these same loads at a longer distance say 300 yards. The load that shoots the lowest has the poorest BC.

I posted this here before. A guy over on 24 hour campfire, actually has Barnes redoing their BC configurations.
He calibrated two Oehler 35 Chronographs together. With one at 205yds.

The Coefficient is a constant factor as distinguished from a variable in mathmatical term.

That factor being the the way the bullet is shaped: smooth, wind resistant, pointed and other variables.

For a bullet to have a high B.C. it will also fly threw the air a little faster.

It's worthy comparing Noslers BC's with Winchesters BC's.

8mm 200g Accubond Nosler .379 Win .477
8mm 180g BT Nosler .357 Win .438

The Winchester BC's are more in-line with the what you would expect. I asked on the Nosler forum why the 8mm BC's were so low and they said because they were done by actual field testing and not by calculation.

I then asked if they were going to re-test all of their bullets since these numbers were so out of whack and all I got was deathly silence. This was about 6 months ago.

quote:

Originally posted by SlowHand:
It's worthy comparing Noslers BC's with Winchesters BC's.

8mm 200g Accubond Nosler .379 Win .477
8mm 180g BT Nosler .357 Win .438

The Winchester BC's are more in-line with the what you would expect. I asked on the Nosler forum why the 8mm BC's were so low and they said because they were done by actual field testing and not by calculation.

I then asked if they were going to re-test all of their bullets since these numbers were so out of whack and all I got was deathly silence. This was about 6 months ago.

Slowhand, thanks for understanding the issue, and for giving an answer related to the question! Very mutch appretiated!!! The "death silence" part reminds me alot of the answer I got from the Barnes people some years ago!

So, gentlemen, we have solved the riddle!

Thanks again, slowhand!

I had the same thing happen with Barnes a year ago.........silence.

quote:

Originally posted by SlowHand:
...I asked on the Nosler forum why the 8mm BC's were so low and they said because they were done by actual field testing and not by calculation.

Yes indeed, if a person takes the time to create their own Drop Chart by actually shooting the Bullets they intend to use, it is a real eye opening experience.

quote:

I then asked if they were going to re-test all of their bullets since these numbers were so out of whack and all I got was deathly silence. This was about 6 months ago.

Got`em. Sounds like they had a "Rolaid Experience" with you putting them on the spot - good for you.