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# How important is bc?

#36
02-02-2010, 06:39 AM
 Silver Member Join Date: Aug 2009 Location: Carlisle, PA Posts: 478
Re: How important is bc?

[QUOTE=Michael Eichele;357296]You could get that info in the 4th edition of the Sierra reloading manual years ago. What is your point? QUOTE]

I was answering a direct question.

Steve asked the question "So, does the boat tail help with wind deflection by reducing the time of flight? "

"So, two bullets, all things being equal, other than the boat tail. Time of flight to a thousand yards is .2 seconds different. How much wind drift difference does that make?

I estimated an answer to his direct question about time difference. He was looking for understanding. When people are looking for understanding it is usually best to answer their direct question. So I did that.

I understand BC. When I'm doing ballistics for my self I don't use time lag. I use QuickTarget Unlimited because it accepts data from QuickLoad and I can enter the G7 BC data from Litz's book in it if that is appropriate for the bullet.

BTW: If it matters, the information I gave on time lag happens to be correct. If you look in Litz's book, Chapter 5, you will find wind drift explained in terms of lag time. The delta Tlag equation I used in the difference reply was derrived from his equations on page 68.

Fitch
#37
02-02-2010, 07:37 AM
 Platinum Member Join Date: Aug 2003 Location: NC, oceanfront Posts: 4,189
Re: How important is bc?

Michael, I believe you're muddling up TOF -vs- LAG within it.
The 168smk may have arrived earlier, but it lagged more. That is, there was a larger differential between it's potential vac arrival(w/resp to MV), and it's actual arrival.
There would be less lag with the big AMAX regardless of MV, because it's velocity drops off slower than the 168.

And with drop, it's just the rate of gravity over a bullet's TOF. Air density plays no role in it, other than to change that TOF, by influencing BC, which causes LAG, and allows increasing drift at the same time.

BC works equally well for both drift and drop, all by itself.
Otherwise, we would have to invoke two BCs. One for drop, and one for drift.
#38
02-02-2010, 10:31 AM
 Official LRH Sponsor Join Date: Mar 2007 Location: Montana Posts: 2,928
Re: How important is bc?

Back to the boat tails. Does the long hunter that works out to 1000 yrds really benefit from the boat tail? I know that it is a very general question, but I am not convinced that it is not more of a sales gimmick than a benefit. It's not like we have a lot of choice, they pretty much all have the boat tail, unless you look at short range bullets.

I think, but I'm not sure, that we all agree that a flat base bullet is inherently more accurate. Do we gain enough from the boat tail to off set the accuracy?

The nose design is the most responsible for how the bullet performs in flight. Am I wrong? As the bullet slows the boat tail becomes more important?

Steve

PS I have very much enjoyed the discussion.
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#39
02-02-2010, 11:54 AM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,830
Re: How important is bc?

Quote:
 Originally Posted by Mikecr Michael, I believe you're muddling up TOF -vs- LAG within it. The 168smk may have arrived earlier, but it lagged more. That is, there was a larger differential between it's potential vac arrival(w/resp to MV), and it's actual arrival. There would be less lag with the big AMAX regardless of MV, because it's velocity drops off slower than the 168. And with drop, it's just the rate of gravity over a bullet's TOF. Air density plays no role in it, other than to change that TOF, by influencing BC, which causes LAG, and allows increasing drift at the same time. BC works equally well for both drift and drop, all by itself. Otherwise, we would have to invoke two BCs. One for drop, and one for drift.
Sorry to confuse you Mike. I didnt get TOF confused with the lag within it. My words may not have sounded clear but I get it. I was just pointing out that it is not TOF that is responsible for windage rather the lag within it. That is, how fast or slow the bullet looses its velocity.

Sorry, I dont agree with you that gravity is the sole function of drop. Drop is directly related to TOF and TOF is directly related to air density. You dont have to invoke 2 BC's for wind and drop. That is why the calculations for drop include gravity as a factor. If there were no air density, the trajectory would be purely parobolic. In other words, the highest point would always be at the exact center of the arc. In the world we live in the highest point in the trajectory is closer to the target than we are. Also, that is why we cannot simply take the angle of a shot's cosine and multiply it by the yardage and aim for the corrected yardage. In a vacume this would work. In our air it does not work. Why? Because gravity is NOT the only influence on the bullet. If gravity was the only influence that simple system would work just fine yet we multiply the cosine by the drop from borline. Why? Because drop from boreline reflects gravity and air density. So yes, air density absolutely plays a role in bullet drop as well as wind.
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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.

Last edited by Michael Eichele; 02-02-2010 at 12:15 PM.
#40
02-02-2010, 12:06 PM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,830
Re: How important is bc?

[QUOTE=Fitch;357326]
Quote:
Below is the quote you replied to in which invoked my reply. FWIW, I realize your numbers are correct. I dont need to look at Litz's book to know you were correct. That was never the point. I was not calling your numbers into question. I have written a couple of different ballistic calculators. Trust me, I understand lag time as ALL of my windage factors are calculated based soley on them. If you read my first post again, you can deduce that my comments were meant to agree with you even if it was from a different angle.

Quote:
 Originally Posted by Jon A Wind drift is less related to time of flight than it is to BC. If you try and make a direct correlation between TOF and wind drift you’re just going to confuse yourself—because a big, slow, high BC bullet can have much less wind drift than a faster lower BC bullet—even if it has a longer time of flight. It’s not a matter of how long the bullet is in the air, it’s a matter of how much effect the air has on the bullet while it is—which is in a sense exactly what BC measures for you. The higher the BC, the less affect the atmosphere has on the bullet; from slowing its velocity to pushing it sideways in the wind (or up or down for up/down drafts).

Sorry if I mussunderstood you. I was refering to your response to Jon A and not Steve. It appeared that you were dissagreeing with him and felt that he was spot on. I cant say you were wrong as you were not. I just thought you missunderstood what he stated.

M
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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.

Last edited by Michael Eichele; 02-02-2010 at 12:44 PM.
#41
02-02-2010, 12:17 PM
 Platinum Member Join Date: Aug 2003 Location: NC, oceanfront Posts: 4,189
Re: How important is bc?

Boat tails are not a hoax, and base drag is a significant part of total drag.

Flat base bullets ARE more accurate.
But at some point/range drift becomes far more difficult to manage than accuracy. This is currently the condition 1Kyd competitors are in, even if they completely deny it. They are all, every single one, shooting heavy per cal bullets(most are boat tails), even though these bullets will not shoot as accurate(as demonstrated closer) as lighter flat base bullets could..
Yet they continually claim 'accuracy' is their top priority... No,,, their setups demonstrate BC first, -followed by accuracy. They get the highest BC bullet shooting as accurately as they can.
Otherwise, they'd be shooting 6PPCs/30BRs at 1kyd.
Oh but those deluding themselves using the recent mid-range mighty mouse cartridges for 1kyd? Well that wheel just keeps going roundy roundy. Their results will be as inconsistant as all who have tried the same in the past.
This is because the devil's in the wind.

You just cannot deny the importance of BC at long distances.
#42
02-02-2010, 12:34 PM
 Platinum Member Join Date: May 2008 Location: South of Canada and North of Wyoming Posts: 6,068
Re: How important is bc?

Steve,

I cant argue whether or not flat base bullets are more accurate than boattails. I dont have enough experience to make a conclusion but I have read a number of opinions that they are so I'll accept it. Question is, how much more accurate are they? Boattailis are apparently accurate enough for 1K plus hunting so I think accuracy is a moot point. And boatail bullets, having a better BC, are less affected by enviromental conditions making them potentially more accurate in a sense at longer ranges.

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