Drag Function?

savage_man

savage_man

New member
Not sure to post this here or on the firearms side... and the winner is.... anyway, could someone break down drag function for me? Maybe while you're at it you could explain ballistics coefficient? I think I have a wrap on it... but maybe not... Thanks for your help in advance.
 
They basically try to quantify the drag on a bullet. All bullets are slowed down by traveling through air. Higher BC means the bullet is more streamlined and slows down less quickly.

Jack
 
Then why do all the bullets for the .224" Bergers bullets rated at a G1? They are all G1... what do I have to do to find a bullet for .224" with a higher drag function?
 
Last edited:
Originally Posted By: savage_manThen why do all the bullets for the .224" Bergers bullets rated at a G1? They are all G1... what do I have to do to find a bullet for .224" with a higher drag function?

Drag function is the efficiency of the body design. All bullets slow down, but some of the same weight and diameter slow down faster than others.

G-1 is for flat based bullets and those with teeny weeny boat tails like the .224 Sierra 52 Matchking - it flies like a flat base.

Flat base and little boat tail bullets are classed as G-1. Bullets that are loooong and have loooong boat tails, are classed as G-7, and have a different numbering system for the BC, and different math to calculate their path through the air.

A G-7 BC of 0.190 is a MUCH HIGHER BC than a G-1 BC of 0.275.

In .224" diameter bullets, G-7 bullets at ~68 grains - the Hornady 68gr match is a G-7, as is the 69gr SMK , and 70gr. Burger.

 
Originally Posted By: savage_manThen why do all the bullets for the .224" Bergers bullets rated at a G1? They are all G1... what do I have to do to find a bullet for .224" with a higher drag function?

All the .224" Berger bullets do NOT have a G-1 drag function... the heaver 224" bullets have a G-7 drag function.


Originally Posted By: Jack RobertsThey basically try to quantify the drag on a bullet. All bullets are slowed down by traveling through air. Higher BC means the bullet is more streamlined and slows down less quickly.

Jack

Well... not really. The question was about drag function, not about drag
frown.gif
frown.gif
frown.gif
 
So maybe I missread their website I was looking at the varmint .224"... Its the combination of the drag function and the BC that I should be looking at?

So the drag function is basically the arrow dynamics of the bullet?

And BC is more of the bullets ability to not be as affected by wind and other variables as opposed to others?

Is there an equasion for all this? I guess a simple google search would answer that... unless they don't search for that too....
laugh.gif

 
Last edited:
Originally Posted By: savage_manSo maybe I missread their website I was looking at the varmint .224"... Its the combination of the drag function and the BC that I should be looking at?

So the drag function is basically the arrow dynamics of the bullet?

And BC is more of the bullets ability to not be as affected by wind and other variables as opposed to others?

Is there an equasion for all this? I guess a simple google search would answer that... unless they don't search for that too....
laugh.gif



Let me put it simply - The BC is the number that is used in a program to (hopefully) predict the flight path of a bullet.

Not all BC are the same, even for the same bullet.

Take a flat based 0.224" Sierra 53gr Match king - a flat base bullet.

Put a bunch in brown bags and give them to a bunch of bullet companies - ask them what the BC is.

You will get a bunch of numbers back - running from 0.235 to 0.260 - depending on how the company computes, figures, or guesses at the BC - it will be a G-1 BC.

Give them all a 0.224", 75gr long base boat tailed bullet, and you will get even a bigger mess.

You'll get BC's from 0.210 to 0.230 (G-7), and BC's from 0.370 to 0.430 (G-1), cuz some companies are not equipped to measure/calculate G-7 BC's.

The point of this is that BC's are not that accurate, and each company has it's own way of computing them - Sierra tests each individual bullet at different speeds, and it's BC's work perfectly in the Sierra Infinity program, but just so-so in other people's ballistic programs.

It's the same with the other bullet makers.


.
 
Also realize that published BC numbers are some times exagerated much like fuel economy numbers. That's why your ballistic program isn't as accurate as you would like it to be.
 
Good post! Good answers!

While we're here, will someone explain Sectional Density numbers, and how some use these numbers instead of BC.

Is it just different numbers to arrive at the same answer?
 
Originally Posted By: ninehorsesGood post! Good answers!

While we're here, will someone explain Sectional Density numbers, and how some use these numbers instead of BC.

Is it just different numbers to arrive at the same answer?

Sectional density is just the weight of the bullet compared to the area (diameter)

So a 100gr 0.224 bullet will have a much higher sectional density that a 100grain 0.45" bullet... it is the weight per square inch.

It is very indirectly related to BC... a very distant cousin.

.
 
Excellent question, I didn't even know what the SD stood for in my Lymans reloading manual... thank you.

Why does it matter? Does it play into the equation to find the BC?
 
Originally Posted By: savage_man

"Why does it matter? Does it play into the equation to find the BC?"



No...

While the casual observer might "think" they do, because higher BC bullets typically have higher SD's, it is possible to have a bullet with a high BC that has a SD lower than a bullet with a lower BC (that made sense, didn't it??)
smile.gif



.
 
Originally Posted By: savage_manIts about at clear as mud... I guess its one of those things I'll understand with time and experiance.

You will not get with time... time has nothing to do with it.

BC is the ability of a bullet to slip through the air - the more streamlined a bullet is, the higher BC it has and the less drag it has.

There were some formulas made to calculate BC many years ago, and the formulas were based on flat based bullets. The formulas worked pretty well.

When the long boat tailed bullet was developed, it worked "OK" with the flat based bullet formulas at high velocities, but as the bullets slowed down, the airflow over the boat tail started taking more effect, and the bullet became even more streamlined.

At this point, the formulas did not work very well. So they developed new formulas and the G-7 was born.

With SD - you can have have a heavy, blunt nosed bullet and compare it with a streamlined bullet that weighs less.

If you have a 30 calibre 220 gr round nose bullet, and compare it to a 155 gr boat tail spitzer, you get...


220 round nose
Sectional Density: 0.331
Ballistics Coefficient: 0.310

155gr Match King
Sectional Density: 0.233
Ballistic Coefficient: 0.504

You can see that the 155gr has a lower SD and a higher BC than the 220 round nose...

So the two are not related.

If you don't get it now, don't worry - it's all just academic crap anyway, and it's not necessary to understand this stuff to shoot a rifle and have fun.


.
 
Originally Posted By: fw707Hey Cat,
how does velocity affect BC numbers?

The way the air flows over the bullet changes with different speeds.

At high speeds the boat tail and flat base behave the same - like flat based bullets. The tail drag is the same area of the base times 14.7 pounds. So I bullet that has a .20" inch area at bore diameter, and a .20" base area... it has a constant tail drag of 3 pounds, until it hits around 600 fps and then it slowly changes.

But a boat tail bullet that has a .20" inch area at bore diameter, and a .10" base area, has tail drag of 3 pounds at very high velocity (3,000+ fps-ish) - but when the velocity gets to the point where the air is starting to follow the slope of the boat tail, the drag starts diminishing, and continues to get less and less as the bullet slows.

As the speed slows, the boat tail bullet has less tail drag... and as Martha Stewart says, "... and that is a good thing!"


.
 
Quote by Catshooter:::If you don't get it now, don't worry - it's all just academic crap anyway, and it's not necessary to understand this stuff to shoot a rifle and have fun.

That is all I needed to read.
 
Like you said I've enjoyed shooting without understanding this, I fact I didn't know BC and SD even existed until the past couple months. I just want to know as much as I can about what's going on and why. Guess that's what you get being an engineers son...

Thanks again.
 


Write your reply...
Back
Top