Sectonal Density?

Lavid2002 · May 12, 2008, 09:29 PM

What is sectional density? I read the formula in my lyman reloading manual and I would like to know how it applies to the shooting worls. Is it how dense the bullet is...giving the shooter an idea of how it will react on targets?

Archie · May 12, 2008, 09:45 PM

of bullet weight to bullet diameter. It is almost a measure of density, but only in relation to the bore diameter.

It has an effect on ballistic coefficient, which is the ability of the bullet to retain velocity in flight. It also has some effect on the burn rate needed to obtain most efficient results from handloading. Typically, the greater sectional density, the greater penetration - ignoring other factors like bullet shape and different velocity.

I've read a number of articles and listened to a number of arguments regarding SD, and so far, haven't been convinced about all of the theories. Still, it is part of what makes reloading a fascinating field of study. Sounds like you're already interested.

Yithian · May 12, 2008, 11:09 PM

SD for the reloader is pretty much null and mute.
The only reason I would need to figure a SD is if I were making my own bullets.

It has no effect in bullet performance other than to tell you the BC at given speeds.
BC's are pretty much given to you by bullet manufacturers nowdays.
It has void effect on terminal ballistics.

So, if you see it, just ignore it.
Manufacturers use it similar to the word "Tactical".
It's part of the sales gimic.

wncchester · May 13, 2008, 07:15 AM

Sectional Density is ONLY the ratio between diameter and weight, has no relationship to Ballistic Coefficent. A .30 cal bullet with a given SD could have a ballistic tip, hollow point, round nose or even be a wad cutter, the SD would remain the same. So would a 150 gr. Barnes solid copper bullet have the same SD as a soft 150 gr. bullet made for the 30-30 but the terminal effect would be vastly different.

In the old days when all bullets were cup and core of pretty much the same materials, SD was useful in estimating how deeply it might penatrate. With today's vast variety of bullet construction SD simply has no meaning. Anyone trying to argue a point around SD is missing the fact that things have changed.

Lavid2002 · May 13, 2008, 12:39 PM

SO for someone making there own bullets, or looking at the same type of bullet like lead made out of the same type of lead COULD use sectional density to determine how much it will penetrate? Thats What I got out of it....
I understand. Im really new to reloading. Perhaps ballistics gel is more efficient than SD?

jimbob86 · May 13, 2008, 12:45 PM

Quote:

Perhaps ballistics gel is more efficient than SD?

For a rough idea of penetration potential, yes.....

First, what is it that you are trying to do? (First, understand the problem.....)

Lavid2002 · May 13, 2008, 12:50 PM

"what are you trying to do"
Understand what sectional density is to broaden my knowledge of the shooting sports. No more, no less. Read it in lymans 48th. Wanted to see if it applied to me in any way, shape, or form. Each load states it so I figured I should know.

jimbob86 · May 13, 2008, 01:04 PM

..... involving practical shooting situations beyond 150 yards or so, then ballistic coefficient (BC) becomes more informative than SD on bullet trajectory. Hitting the quarry in the first place is more important than what you hit them with, provided you don't try anthing ridiculous (bullets constructed for varmits out of really small bores, for example).

If you use a commercially available bullet, its BC should be listed in that company's reloading manual, as will its SD, though I am not sure what use knowing your bullet's SD would be.......

Jim Watson · May 13, 2008, 02:01 PM

Sectional density is the ratio of the bullet weight to the SQUARE of diameter.

Back when bullets were either solid lead or a simple cup jacket and core, sectional density was a pretty good predictor of penetration. If you care to buy premium bullets with trick construction, it matters a lot less.

Ballistic coefficient is sectional density divided by a form factor expressing the "streamlining" of the bullet and is what you need to figure downrange trajectory and retained velocity.

Lawyer Daggit · May 13, 2008, 05:30 PM

I agree with wnchester and Jim Watson's comments. Only that I would add that if using a bullet with high sectional density one may more comfortably elect to use a cheaper 'unsophisticated' bullet like the old Hornady Weldcore, but if you are using a calibre with poor SD, if you wish to take large game and take difficult shots (ie not the traditional side on to heart / lungs) you would be well placed obtaining one of today's high performance bullets.

This may note effect Americans very much, but in many developing countries in the World US premium bullets are extremely expensive.

Erik · May 18, 2008, 08:52 PM

As noted, sectional density is a bullet's weight in pounds divided by the square of its diameter in inches. Bullets with greater sectional density tend to penetrate deeper than those with lesser sectional density.

It may be used for "at a glance" estimation and comparison of penetration performance. How? Bullets of similar sectional densities, propelled at similar velocities, and exhibiting similar percentages of expansion typically penetrate to similar depths.

Not sure what the sectional density of a given bullet is? Use the following formula:

M ÷ 7000 ÷ d2 = sectional density

Step 1:
Divide M (M = bullet weight in grains) by 7000:

Step 2:
Determine d2 (d2 = the square of bullet diameter in inches):

Step 3:
Divide the quotient of step 1 by the product of step 2:

WESHOOT2 · May 19, 2008, 07:02 AM

I consider SD significant for handgun rds developed to shoot people.
It offers a window of possible penetration.

More weight behind the hole suggests to me deeper penetration, regardless of bullet construction.

Not hard science (yet?).
IMO&E WAY more important than "void effect on terminal ballistics".

(think: two bullets of similar construction and same diameter, one with a higher SD. Which will penetrate further in the same media?)

Yithian · May 20, 2008, 12:33 AM

It depends on said construction.
If it is a pointed steel round, it will penetrate farther than a soft lead one.
What about the 'dreaded' Teflon bullets?
Is the target wearing armor?
Is it a 300 Lb wild boar?

SD is a good way of misjudging a shot, IMO.
And, I am not alone.
Neither are you tho.

I go by what I know and have experienced.
A perfect example...
My 204RUG loaded with 39gr Sierra BlitzKings will not penetrate hairy hides.
The same rifle loaded with 40gr V-Max's sinks in a minimum of 2 inches, and then explodes.
They have the same relative SD, yet the BK's are lacking, and the V-Max's will take 200 Lb wild hogs.
V-Max 40gr SD = 0.137
V-Max 32gr SD = 0.110
BK's SD = 0.134
Construction of the projectile.
And no, the lighter weight means little. A 32gr V-max has taken 140 Lb hogs, by me.
The BK has zero harvests by me so far, unless it was a small animal like a squirrel.
I shoot in the ear.

Don't rely on a single factor to judge bullet performance.
The logic of SD used to work, to a degree, but is severely flawed today.

Yithian · May 20, 2008, 01:28 AM

Sorry you were talking pistol and I, rifle.
I had a hard time relocating this site, so I just decided to post twice.
Consider this site when you think Sectional Density has any part in the Terminal Ballistics reported.

It is a unbiased comparison of various defence loads for handgun ammunition.
Question: How difficult is it for you to find any mention of SD?

http://ammo.ar15.com/Self_Defense_Ammo_FAQ/index.htm

Great info BTW.
There aint nothing better than using ammo, to determine for yourself what it does, and does not do.

May 12, 2008, 09:29 PM	#1
Lavid2002 Senior Member Join Date: April 6, 2007 Posts: 2,568	Sectonal Density? What is sectional density? I read the formula in my lyman reloading manual and I would like to know how it applies to the shooting worls. Is it how dense the bullet is...giving the shooter an idea of how it will react on targets? __________________ Math>Grammar

May 12, 2008, 09:45 PM	#2
Archie Senior Member Join Date: May 26, 2000 Location: Hastings, Nebrasksa - the Hear Posts: 2,209	Sectional Density is the ratio of bullet weight to bullet diameter. It is almost a measure of density, but only in relation to the bore diameter. It has an effect on ballistic coefficient, which is the ability of the bullet to retain velocity in flight. It also has some effect on the burn rate needed to obtain most efficient results from handloading. Typically, the greater sectional density, the greater penetration - ignoring other factors like bullet shape and different velocity. I've read a number of articles and listened to a number of arguments regarding SD, and so far, haven't been convinced about all of the theories. Still, it is part of what makes reloading a fascinating field of study. Sounds like you're already interested. __________________ There ain't no free lunch, except Jesus. Archie Check out updated journal at http://oldmanmontgomery.wordpress.com/

May 12, 2008, 11:09 PM	#3
Yithian Senior Member Join Date: June 7, 2007 Location: Texas Posts: 719	SD for the reloader is pretty much null and mute. The only reason I would need to figure a SD is if I were making my own bullets. It has no effect in bullet performance other than to tell you the BC at given speeds. BC's are pretty much given to you by bullet manufacturers nowdays. It has void effect on terminal ballistics. So, if you see it, just ignore it. Manufacturers use it similar to the word "Tactical". It's part of the sales gimic. __________________ Pondering the differences, terminally, between the V-Max and the A-Max.

May 13, 2008, 12:39 PM	#5
Lavid2002 Senior Member Join Date: April 6, 2007 Posts: 2,568	Alright SO for someone making there own bullets, or looking at the same type of bullet like lead made out of the same type of lead COULD use sectional density to determine how much it will penetrate? Thats What I got out of it.... I understand. Im really new to reloading. Perhaps ballistics gel is more efficient than SD? __________________ Math>Grammar

May 13, 2008, 12:50 PM	#7
Lavid2002 Senior Member Join Date: April 6, 2007 Posts: 2,568	"what are you trying to do" Understand what sectional density is to broaden my knowledge of the shooting sports. No more, no less. Read it in lymans 48th. Wanted to see if it applied to me in any way, shape, or form. Each load states it so I figured I should know. __________________ Math>Grammar

May 13, 2008, 07:15 AM	#4
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	Sectional Density is ONLY the ratio between diameter and weight, has no relationship to Ballistic Coefficent. A .30 cal bullet with a given SD could have a ballistic tip, hollow point, round nose or even be a wad cutter, the SD would remain the same. So would a 150 gr. Barnes solid copper bullet have the same SD as a soft 150 gr. bullet made for the 30-30 but the terminal effect would be vastly different. In the old days when all bullets were cup and core of pretty much the same materials, SD was useful in estimating how deeply it might penatrate. With today's vast variety of bullet construction SD simply has no meaning. Anyone trying to argue a point around SD is missing the fact that things have changed.

May 13, 2008, 01:04 PM	#8
jimbob86 Junior member Join Date: October 4, 2007 Location: All the way to NEBRASKA Posts: 8,722	If you are handloading for hunting applications..... ..... involving practical shooting situations beyond 150 yards or so, then ballistic coefficient (BC) becomes more informative than SD on bullet trajectory. Hitting the quarry in the first place is more important than what you hit them with, provided you don't try anthing ridiculous (bullets constructed for varmits out of really small bores, for example). If you use a commercially available bullet, its BC should be listed in that company's reloading manual, as will its SD, though I am not sure what use knowing your bullet's SD would be.......

May 13, 2008, 02:01 PM	#9
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,543	Sectional density is the ratio of the bullet weight to the SQUARE of diameter. Back when bullets were either solid lead or a simple cup jacket and core, sectional density was a pretty good predictor of penetration. If you care to buy premium bullets with trick construction, it matters a lot less. Ballistic coefficient is sectional density divided by a form factor expressing the "streamlining" of the bullet and is what you need to figure downrange trajectory and retained velocity.

May 13, 2008, 05:30 PM	#10
Lawyer Daggit Senior Member Join Date: December 5, 2004 Posts: 1,181	I agree with wnchester and Jim Watson's comments. Only that I would add that if using a bullet with high sectional density one may more comfortably elect to use a cheaper 'unsophisticated' bullet like the old Hornady Weldcore, but if you are using a calibre with poor SD, if you wish to take large game and take difficult shots (ie not the traditional side on to heart / lungs) you would be well placed obtaining one of today's high performance bullets. This may note effect Americans very much, but in many developing countries in the World US premium bullets are extremely expensive.

May 18, 2008, 08:52 PM	#11
Erik Senior Member Join Date: December 24, 1999 Location: America Posts: 3,479	As noted, sectional density is a bullet's weight in pounds divided by the square of its diameter in inches. Bullets with greater sectional density tend to penetrate deeper than those with lesser sectional density. It may be used for "at a glance" estimation and comparison of penetration performance. How? Bullets of similar sectional densities, propelled at similar velocities, and exhibiting similar percentages of expansion typically penetrate to similar depths. Not sure what the sectional density of a given bullet is? Use the following formula: M ÷ 7000 ÷ d2 = sectional density Step 1: Divide M (M = bullet weight in grains) by 7000: Step 2: Determine d2 (d2 = the square of bullet diameter in inches): Step 3: Divide the quotient of step 1 by the product of step 2: __________________ Meriam Webster's: Main Entry: ci·vil·ian Pronunciation: \sə-ˈvil-yən also -ˈvi-yən\, Function: noun, Date: 14th century, 1: a specialist in Roman or modern civil law, 2 a: one not on active duty in the armed services or not on a police or firefighting force b: outsider 1, — civilian adjective

May 19, 2008, 07:02 AM	#12
WESHOOT2 Senior Member Join Date: February 20, 1999 Location: home on the range; Vermont (Caspian country) Posts: 14,324	"Weight behind the hole" I consider SD significant for handgun rds developed to shoot people. It offers a window of possible penetration. More weight behind the hole suggests to me deeper penetration, regardless of bullet construction. Not hard science (yet?). IMO&E WAY more important than "void effect on terminal ballistics". (think: two bullets of similar construction and same diameter, one with a higher SD. Which will penetrate further in the same media?) __________________ . "all my ammo is mostly retired factory ammo"

May 20, 2008, 12:33 AM	#13
Yithian Senior Member Join Date: June 7, 2007 Location: Texas Posts: 719	It depends on said construction. If it is a pointed steel round, it will penetrate farther than a soft lead one. What about the 'dreaded' Teflon bullets? Is the target wearing armor? Is it a 300 Lb wild boar? SD is a good way of misjudging a shot, IMO. And, I am not alone. Neither are you tho. I go by what I know and have experienced. A perfect example... My 204RUG loaded with 39gr Sierra BlitzKings will not penetrate hairy hides. The same rifle loaded with 40gr V-Max's sinks in a minimum of 2 inches, and then explodes. They have the same relative SD, yet the BK's are lacking, and the V-Max's will take 200 Lb wild hogs. V-Max 40gr SD = 0.137 V-Max 32gr SD = 0.110 BK's SD = 0.134 Construction of the projectile. And no, the lighter weight means little. A 32gr V-max has taken 140 Lb hogs, by me. The BK has zero harvests by me so far, unless it was a small animal like a squirrel. I shoot in the ear. Don't rely on a single factor to judge bullet performance. The logic of SD used to work, to a degree, but is severely flawed today. __________________ Pondering the differences, terminally, between the V-Max and the A-Max.

May 20, 2008, 01:28 AM	#14
Yithian Senior Member Join Date: June 7, 2007 Location: Texas Posts: 719	Sorry you were talking pistol and I, rifle. I had a hard time relocating this site, so I just decided to post twice. Consider this site when you think Sectional Density has any part in the Terminal Ballistics reported. It is a unbiased comparison of various defence loads for handgun ammunition. Question: How difficult is it for you to find any mention of SD? http://ammo.ar15.com/Self_Defense_Ammo_FAQ/index.htm Great info BTW. There aint nothing better than using ammo, to determine for yourself what it does, and does not do. __________________ Pondering the differences, terminally, between the V-Max and the A-Max.