# ballistic coefficient on bullets

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by new shooter, Dec 9, 2006.

1. ### new shooterWell-Known Member

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question on custom bullet companies? I see some of these companies don't list their BC (ballistic coefficient) of their bullets. i understand there has been some arguments over their BC (like richard's wild cat bullets). Is there not a non-biased company that could check their BC; so we hand loaders would have all the facts. Why would you spend a dollar for ONE bullet when you would not know the BC? when the bullet you are using might have more BC and then you would be wasting your money and time. if this question seems ignorant please forgive as I am new at this. thanks for the replies

2. ### Michael EicheleWell-Known Member

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In alot of cases (all cases), differant bullets will have a differant BC for a given powder charge, load density, barrel length, twist rate, velocity, air density, and I am sure a few other things we havent discovered yet.

It is almost always a waste of time to use the factories published BC for anything past 400-500 yards anyway. So you might as well just try differant bullets and figure out what they are dropping in what air density. Then cross referancing this real world data with a good ballistic calculator, you can come up with a real BC for your rifle/load combo. Published BC's are only an average based on a controlled enviornment and specifec barrel length/twist combo's. Trust me, it is no waste of time to fire away and figure out the real BC in the real world with your equipment.

Also, if youre interested in using a particular bullet with no published BC and want a rough estimate, BC can be calculated. Please note that sometimes this will be close and sometimes it might be way off the mark. Most of the time, it will give you an idea based on physics. It takes a BC calculator to do this. These can be found in several ballistic calculators both PC and web based.

It is also more important to have a bullet that shoots good in your rifle with a lower BC than one that shoots bad yet boasts a high one. Obviously this is to a point of balance as a really low BC will have a detrimental effect on overall performance at 1000 yards. At that point, sure 1 MOA 100 yard accuracy and a high BC would be better than 1/2 MOA 100 yard accuracy and a very low BC due to wind drift and other factors.

Bottom line: Find a bullet that shoot really good in your rifle that has the highest BC possible that maintains acceptable accuracy bearing in mind that the bullets with the highest BC's in your rifle might not shoot worth a crap.

3. ### CatShooterWell-Known Member

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[ QUOTE ]
In alot of cases (all cases), differant bullets will have a differant BC for a given powder charge, load density, barrel length, twist rate, velocity, air density, and I am sure a few other things we havent discovered yet.

[/ QUOTE ]

I'm sorry... but the BC of a bullet has NOTHING to do with powder, load density, twist, primers, or anything else internal to the rifle...

... BC starts when the bullet hits the air, AFTER it leaves the barrel, and it only relates to the bullet's ability to pass through the air.

Himidity, air density and temperature do NOT affect BC.

BC is a mathamatical quality of the shape of the bullet... nothing more.

.

4. ### royinidahoWriters Guild

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Not being a smartA here but that non-biased company would be you!

The BC is the BC for only one set of atmospheric/environmental conditions. Change any of the atmospheric/environmental conditions and the effective BC changes. At least that's my understanding.

5. ### MikecrWell-Known Member

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I agree with Roy on the non-biased company being you. There is nobody else.. No standards, and no independant group with which to establish standards. SAAMI? NRA? IBS? NOPE!!

Catshooter is right also, w/regard to BC claimed under StdMetro or ICAO conditions. Who knows what any maker bases their BC on though. And local BC will have to be adjusted for conditions, unless you have the means to adjust the drag curve. Depends on your ballistic software.
BC would be a constant with a matching drag curve(not G1), but because software available does not reference a matched curve for your bullet, under the specific -local conditions, apparent BC goes all over the place.
And worst of all, bullets are not made to ANY standard. Every lot is different from any maker. So their BC is bogus to begin with.

6. ### CatShooterWell-Known Member

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Actually... Mike and Roy are both on to it.

Back in the days when I was a young grasshopper, BC was determined by the famous "Dupont chart", which I still have a copy. It is a large wall chart that has figures of bullets, and some basic numbers, and you add or subtract points for certin features - you add for a boat tail, you subtract for a round nose. etc... it decorates my loading room now - I LOVE IT! /ubbthreads/images/graemlins/wink.gif

There are several protocols for determining BC... Sierra came out with their ballistic program many years ago (15-ish??), and it is sooooo bad, that each bullet has to be tested at many velocities, and different numbers assigned to it, so the program will reasonable track.

It is BADD SOFTWARE. But you can be reasonable sure that your Sierra bullet will track as predicted (but not always).

But it will not do a very good job of tracking other company's bullets.

Other companies measure the lost speed over a fixed distance (usually 200 yds) and give the bullet a fixed BC based on the lost velocity over that one tract at that one muzzle velocity.

There are sophisticated programs that will compute the BC and do the alterations BC as the bullet speed changes...

All these programs start at standard "mets".

The barometric pressure and the temperature are two variables that don't affect the BC, but the formula's must adjust for, because they affect the density of the air.

There are some bullet companies that STILL use the Dupont chart to rate their bullets.

So bullet "A" with a BC of .375 is NOT the same as bullet "B" or "C" or "D" with a BC of .375.

So it's kinda foggy... but I don't think we want the bullet police to come in and regulate it.

.

7. ### Michael EicheleWell-Known Member

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[ QUOTE ]
Himidity, air density and temperature do NOT affect BC.

BC is a mathamatical quality of the shape of the bullet... nothing more.

[/ QUOTE ]

I wouldnt bet anything you cant afford to loose on that. What I posted is based on fact, not fiction. Using only form and length and diameter is fiction. I will give you this, the form, length, diameter and weight have more to do with it than any other factor however, these figures are not the only thing that go into it. You had better spend a little more time doing research as well as time behind differant rifles doing a little more experimenting before you continue to claim every thing I say on this site as false.

8. ### Michael EicheleWell-Known Member

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[ QUOTE ]
The BC is the BC for only one set of atmospheric/environmental conditions. Change any of the atmospheric/environmental conditions and the effective BC changes. At least that's my understanding.

[/ QUOTE ]

Now that I can agree with.

catshooter quoted:

[ QUOTE ]
Himidity, air density and temperature do NOT affect BC.

[/ QUOTE ]

Then catshooter quoted
[ QUOTE ]
Actually... Mike and Roy are both on to it.

[/ QUOTE ]

RII quoted:
[ QUOTE ]
The BC is the BC for only one set of atmospheric/environmental conditions. Change any of the atmospheric/environmental conditions and the effective BC changes.

[/ QUOTE ]

Mike quoted:
[ QUOTE ]
And local BC will have to be adjusted for conditions, unless you have the means to adjust the drag curve. Depends on your ballistic software.
BC would be a constant with a matching drag curve(not G1), but because software available does not reference a matched curve for your bullet, under the specific -local conditions, apparent BC goes all over the place.
And worst of all, bullets are not made to ANY standard. Every lot is different from any maker. So their BC is bogus to begin with.

[/ QUOTE ]

So really catshooter, you agree that there are other factors than just form. Am I right.

That means to me that you just dont like me. You know, you say one thing then say another....
Did I piss you off somewhere?

9. ### CatShooterWell-Known Member

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[/ QUOTE ] So really catshooter, you agree that there are other factors than just form. Am I right.

That means to me that you just dont like me. You know, you say one thing then say another....
Did I piss you off somewhere?

[/ QUOTE ]

What???... is your problem???

[ QUOTE ]
In alot of cases (all cases), differant bullets will have a differant BC for a given powder charge, load density, barrel length, twist rate, velocity, air density, and I am sure a few other things we havent discovered yet.

[/ QUOTE ]

This is NOT true.

[ QUOTE ]
It is almost always a waste of time to use the factories published BC for anything past 400-500 yards anyway.

[/ QUOTE ]

This is NOT true.

The following group was shot at 405 yards.

The rifle was built, and the first 35 rounds were shot to get the velocity, and 100yd zero.

Rounds 36, 37, and 38 were fired at the target (405 yds) based on come-ups dialed from a ballistic program...

http://www.snipercountry.com/images/Pablito-M24-0.46-target.jpg

[ QUOTE ]
So you might as well just try differant bullets and figure out what they are dropping in what air density. Then cross referancing this real world data with a good ballistic calculator, you can come up with a real BC for your rifle/load combo.

[/ QUOTE ]

Back engineering BCs does not work, unless you have a lot of time on your hands.

[ QUOTE ]
Published BC's are only an average based on a controlled enviornment and specifec barrel length/twist combo's.

[/ QUOTE ]

This is NOT true.

[ QUOTE ]
Trust me,

[/ QUOTE ]

HA!!!

[ QUOTE ]
it is no waste of time to fire away and figure out the real BC in the real world with your equipment.

[/ QUOTE ]

What you are talking about is developing your own drop chart - you are NOT developing a BC... so NOT true!

I don't either like or dislike you... I don't give a rats ass...

You need to get a grip and not let your fragle ego take hold of you.

.

10. ### Michael EicheleWell-Known Member

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On a calm note,

I didnt say it was always a waste of time to use the factory published BC for 1K shooting. I said it is almost always a waste. Your example is of 405 yards NOT 1K. I dont doubt that you have used a factory BC and come out with a perfect hit at 1K. No proof needed here. I believe it. I have done the same myself. However, please dont believe that you can always use the published BC for every bullet and hit perfectly in every circumstance. I dont dont care what you believe or dont. Its your targets. Just please dont quote me and say it is absolutly not true unless you KNOW for a fact it is total bull crap. I can back up every thing I stated.

I am done arguing with you here and in every other post, Go ahead, swing away at me.

11. ### CatShooterWell-Known Member

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[ QUOTE ]
I am done arguing with you here and in every other post, Go ahead, swing away at me.

[/ QUOTE ]

What the hell are you talking about... I have NEVER had an argument with you on ANY other post.

Are you mixing me up with someone else, or is it that everyone argues with you, and we all look the same?

.

12. ### Michael EicheleWell-Known Member

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Not continuing to argue, just clarifying. Your're right, we havent argued in any other posts. I just meant, future posts. I will not be partaking in any future arguments with you. And no, nobody else argues with me here. Some have shown me where I was wrong, or even showed me another way to look at something, but no one has ever quoted me and yelled back that it simply wasent true.

13. ### Michael EicheleWell-Known Member

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New shooter,

sorry about the hijacked thread. Back to your original question, posted are some links to some good reads about BC's that are from more than reputable sources. These will help you understand the BC better and what goes into it.

The statment at the bottom of this first article sums it up very well.
http://www.shootingsoftware.com/coefficients.htm

http://www.riflebarrels.com/articles/bullets_ballastics/measure_ballistic_coefficients.htm

This last one is from Sierra and is most likely the most informative for most shooters interested in this topic.

http://www.exteriorballistics.com/ebexplained/4th/44.cfm

With this you should be able to draw your own educated conclusions based on credible scources and not mine or anybody elses.

14. ### goodgrouperWell-Known Member

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I don't want to flare up a fire here but the barrel does have an affect on bc. The twist rate is directly responsible in part for the stability of the bullet and how it flies through the air. Understabilized bullets with a rated bc of say .7 obviously do not fly as efficiently as a properly stabilized bullet with a bc of .7 resulting in a much lower bc. On the flip side, a bullet that is overstabilized also has an altered bc because of the agressive yaw of repose and the nose might not follow the arc of the trajectory although it will be quite a small difference. Much smaller reduction in bc than if the bullet is understabilized of course.

Badly worn barrels also change the bc of the bullet as they degrade the aerodynamics of the bullet jacket. Over the course of the barrels life, you can usually see a small degredation of bc over time.

Now, for purposes of actually trying to hit a target, the shooter must know how air density and air temp among other atmospherics change the path of his bullet. Or just get a ballistic program and carry it with you in the field and it will correct the the trajectory for you and give the proper information.

Clear as mud right?