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ballistic coefficient on bullets

 
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  #1  
Old 12-09-2006, 03:13 PM
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ballistic coefficient on bullets

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
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Old 12-09-2006, 09:58 PM
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Re: ballistic coefficient on bullets

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.
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Old 12-10-2006, 08:31 AM
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Re: ballistic coefficient on bullets

[ 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.


.
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Old 12-10-2006, 09:07 AM
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Re: ballistic coefficient on bullets

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.
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Old 12-10-2006, 01:05 PM
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Re: ballistic coefficient on bullets

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.
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Old 12-10-2006, 02:13 PM
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Re: ballistic coefficient on bullets

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! [img]/ubbthreads/images/graemlins/wink.gif[/img]

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.

.
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Old 12-10-2006, 02:19 PM
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Re: ballistic coefficient on bullets

[ 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.
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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