Where do you stand on Sectional Density?

Gday @DaddyFlip
Your joined on the vote count now & I hunt Africa let alone a few aussie critters lol

SD is Completely irrelevant to terminals
TSD is what needs to be understood first & then that can even be taken to another level & what to call that @michael458 would have a better idea than me

Shock horror to some im about to use a less than .2 SD on elephant all going well if we get my mates first & don’t worry it was tested in media & aussie critters which although those 2 testing substances showed different results & those results were , I could catch the bullet in the media & failed many times too catch one in any critter any angle lol
Cheers

At the risk of being Captain Obvious, SD is just one of the factors that determine a bullet’s potential penetration. It’s a number that describes the design of a bullet. Longer, heavier bullets tend to penetrate deeper, all things being equal. Bullet construction is another important factor. Good metallurgy and tight tolerances can make a bullet tougher and therefore better able to penetrate. The other variable is velocity. Faster is generally better….until it isn’t.

I pay no attention to the SD of the bullets I hunt with. I select proven performers based on my experience and the experience of people I trust. Generally, crusty curmudgeons like myself. I leave the lab coat ballistics to others.

Wyatt Smith said:

Op were you talking about solid bullets or expanding. It’s been proven that for solids it’s one of the least important factors for deep penetration, although some companies try to use it to cover up flaws in the more important like meplat size and nose profile.

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More specifically for expanding. I was curious because it seems people think that a 300 grain 375 is a great bullet for Buffalo but a 300 or even 350 grain 458 bullet is undergunned. I have no experience in Africa or with a 375, so I was hoping people with more experience than me could weigh in on the matter given that a lot of reading about it is either old or direct references to the old material

NoStepOnSnek said:

More specifically for expanding. I was curious because it seems people think that a 300 grain 375 is a great bullet for Buffalo but a 300 or even 350 grain 458 bullet is undergunned. I have no experience in Africa or with a 375, so I was hoping people with more experience than me could weigh in on the matter given that a lot of reading about it is either old or direct references to the old material

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This is where I feel sectional density should at least be considered in all the different factors that go into choosing a bullet. A 300 grain 458 caliber bullet has a sectional density of .2. It may very well get the job done, but it definitely lacks "Momentum Retention" and therefore has less penetration potential. The larger diameter and shorter profile are a poor combination for penetration.

Look at it like this. A big rig (truck only) running into your house at let's say 25 miles per hour. The damage will definitely be significant. Now imagine the same truck with a 50 foot, fully loaded trailer attached hits your house at 25 miles per hour. Probably going in one side and out the other. With the trailer attached the sectional density went way up and maximized Momentum Retention.

Fordy said:

Gday @DaddyFlip
Your joined on the vote count now & I hunt Africa let alone a few aussie critters lol

SD is Completely irrelevant to terminals
TSD is what needs to be understood first & then that can even be taken to another level & what to call that @michael458 would have a better idea than me

Shock horror to some im about to use a less than .2 SD on elephant all going well if we get my mates first & don’t worry it was tested in media & aussie critters which although those 2 testing substances showed different results & those results were , I could catch the bullet in the media & failed many times too catch one in any critter any angle lol
Cheers

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I hope you're elephant hunt goes well and that you drop that big guy in his tracks. I'm very curious about what caliber and bullet weight you have chosen to get a sectional density that low. Would you mind sharing.

Every few years this SD discussion occurs- and strangely enough, no one's mind is changed. Surprise Surprise Surprise.

rookhawk said:

This is absolutely true @Wyatt Smith . But SD and BC seem to go together. SD+BC really matter in heavy-for-caliber bullets in lightweight calibers. I think you and I would both extol the virtues of a 140gr 6.5x55, or a 175gr 7x57, or a 220gr 300HH, or even a 250gr 318 WR. Is it the BC, the SD, or both combined in a very heavy bullet at moderate velocity that makes these load configurations so darned good? Probably a mix of all along with a lot of "hang time" where a bullet bores a slow, steady hole into the animal rather than zip right through.

But at medium and large bore calibers at moderate range? I delight in a nice round nose bullet that feeds and expands perfectly, even if the SD or BC seems lethargic.

When all other factors are discounted, the biggest hole in the vital area of an animal wins.

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Personally, I like and prefer heavy for caliber bullets. Heavy for caliber bullets naturally have a higher SD and often a higher BC. In my opinion SD is only useful for comparing bullets of different calibers, for example a 270 vs a 7mm. If the bullets are of the same caliber, weight is sufficient.
Round nose bullets are my favorite, the 175 7mm, 220 30 caliber. The 170 grain in the 30-30 and 32 Winchester special is pure magic and medium sized game at 100 yards and less.

I thought of a new twist on the SD topic. Before my hunting days ended over 20 years ago, I owned a .458 shooting 420- and 540-grain bullets; that's SDs of .286 and .368. The cartridge manufacturer never mentioned SD in those days (they do now on one of their offerings) but touted the John "Pondoro" Taylor Knockout Value (TKO) = (weight x velocity x diameter)/7000. The 420 was advertised as a plains game / big cat load while the 540 could be used for buff and ele. There were (and are) testimonials of good performance in Africa and other hunting grounds with these loads. Sounded good and reasonable on the surface; I used to daydream of hunting big game with this setup.

Problem was, the .458 was actually a Marlin 45-70 lever action; albeit, a Jim Brockman custom built Beast model (probably 1998 vintage I think). The carts were Garrett hard cast lead. The velocities were 1850 and 1550 fps resulting in KE of 2900 ft-lb for the 540 (3200 for the 420). I know the Marlin has been used successfully in Africa, but in general I think lever actions are frowned upon for DG. To summarize:

SD = .368 (great)
Weight = 540-grains; heavy for caliber (great)
Diameter = .458-inch (great)
Meplat = .360-inch (great)
Bullet = hard cast lead (mixed reviews)
Caliber = 45-70 Govt. (not so great)
Velocity = 1550 FPS (not so great)
Energy = 2880 ft-lb (not so great)
Rifle = Marlin lever action (mixed reviews)

For most hunters, I think one of the bottom five factors might weigh heavily and exclude this setup from consideration, even though the first four factors are excellent. SD didn't tell the whole story.

Garrett now has a 500-grain copper clad steel jacketed FN at 1550 they enthusiastically endorse for DG. The 540-grain is specified for the big bears.

When y'all are done discussing SD you can expand the discussion to what I refer to as a "Variable Ballistic Coefficient". It is only slightly related to SD in that the momentum of the mass behind the point is considered, but the issue is point shape, angle from the centerline and frontal area. In basics it is how does the bullet's shape transform when it encounters resistance to a very low Ballistic Coefficient- best case scenario is the point becomes flat (relative to the centerline) with a frontal area of 2 to three times that of the non-expanded bullet.

My standpoint:
Heavy for caliber bullets. This in general will mean higher SD.

But I am not thinking in terms of SD.
Mass penetrates, not the velocity.
So, above poll choices do not reflect my approach.

DaddyFlip said:

No need to cast aspersions. Would you hunt DG with a 7mm Rem Mag, 190gr. match bullet

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No the velocity is too high.....
I have killed dg game with a 7x57mm with 170 and 175 gr and 3006 with 220gr...

I prefer heavy for caliber bullets with high sd in legal DG calibers and moderate velocity 2200 to 2400fps eg.

9.3 286gr and 300gr
375 300gr, 340gr, 350gr and 380gr
510 570gr and 600gr

Now you can multiply divide subtract add and come.up with whatever you want but I will use heavy for caliber high sd bullets on dg everytime

IvW said:

I will use heavy for caliber high sd bullets on dg everytime

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The SD is a by-product coincidental to the heavy for caliber, not a correlation.

Ray B said:

The SD is a by-product coincidental to the heavy for caliber, not a correlation.

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Whatever it is it works

BeeMaa said:

Calling @michael458.

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Well, Here I Am. Now what? HEH.................. Sometimes I answer the phone knowing it is one of my kids, this pisses them off ("What do you Want? If I wanted to talk to you I would call YOU!) In jest of course, but it is funny to get their reactions.

Sectional Density?.......... I answered "It does not Matter At All" One of 4 currently at this moment. Many are beginning to realize that there are other factors involved that have higher import than SD. SD was made up by writers and manufacturers to give some sort of numerical importance to a bullet, without proper study of what it even means, if anything at all. There really is not much importance to SD, at least not while a bullet is sitting on the shelf in your loading room. SD alone tells you nothing. As BeeMaa says below, "There are a number of factors involved that make a bullet penetrate"

BeeMaa said:

There are a number of factors that make a bullet penetrate, expand or blow up. And any of those can be the desired outcome. Sectional density is important, but I'd put it close to the bottom of the list. All of the factors above it will impact the sectional density to achieve the desired effect.

Material(s) used
Construction and heat treatments/process of bonding or forming
Bullet shape
Frontal area/tip shape
Length
Speed
Weight
Sectional density

This only really works when comparing similar bullets trying to achieve the same results. So take a 375H&H 270 grain TSX and compare it to a 300 grain TSX. Even then, it would depend on what I'm hunting , at what range and what outcome I'm looking for.

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@BeeMaa is a wise man.

When discussing SD it has to be broken into two separate Categories...... SOLIDS.......... Expanding/Trauma Inflicting. These two Categories treat SD in completely different ways.

We will start with Solids First, they are much easier. There are 8 Absolute Known Factors of Solid Terminal Performance, and the last Factor, and least Important Factor is Sectional Density. All other factors have more bearing on how a solid penetrates.

#1 Meplat Percentage of Caliber

#2 Nose Profile

#3 Construction & Material

#4 Nose Projection

#5 Radius Edge of Meplat

Above Factors are in Bullet Design

#6 Velocity

#7 Barrel Twist Rate

#8 Sectional Density


#8 Sectional Density
Sectional Density will ONLY BE A FACTOR with two bullets that are exactly the same in every other Factor or aspect. Factors #1 and #2 far outweigh Sectional Density in the terminal performance of Solids. We can take a properly designed 458 caliber 325 gr Solid and far out penetrate in depth and stability a poorly designed 550 gr 458 caliber bullet....... My son recently shot a medium sized elephant at 10 yards, perfectly executed side brain shot, with a 350 gr .474 caliber properly designed solid at 2200 fps. This bullet exited the head on the far side and still may be going for all I know. A 350 gr .474 caliber bullet has a sectional density of .223, and I personally would choose this little 350 gr bullet over the Woodleigh 500 gr RN FMJ at .4725 (ones I have here) any and every day for any mission............

Example;

Sectional Density .313


Sectional Density .374



Sectional Density .221





I think that should be self explanatory........................

Expanding or Trauma Inflicting Bullets.

Now we enter a world where Sectional Density of Expanding or Trauma Inflicting bullet that is setting on the shelf, or in the box they came in is useless and will remain the same until it is fired, and begins terminal penetration, then the SD changes dramatically.

Terminal Sectional Density will not tell you how deep a bullet will penetrate, but it will tell you WHY.

Only Terminal Sectional Density has any bearing at all.

There are hundreds of different expanding type bullets out there, bonded (Swift A), Monolithic (Barnes TSX) Go all to hell (Nosler Ballistic Tips) and so forth, get the picture of how all these work? Now, picture this, while they are sitting on the shelf in your loading room, if they are the same weight and caliber, every single one has the exact same Sectional Density. Do all of them penetrate to the exact same depth? Do all of them dump the same amount of Trauma on tissue in the same way? Of course they do not.

Now, in the last 15 years or so, enter Generation 1 and Generation II CNC Machined bullets, and the dynamic changes again. Now we have a Swift A Frame, Barnes TSX, Nosler BT, and CEB Raptor and Copper Hammer bullets sitting on the shelf, all same caliber, all same weight, all same SD. But now, we are going to through the proverbial Monkey Wrench in the mix, and the Generation 1 and II are going to have LESS SD on the shelf.

Lets use this example a 500 gr Swift A Frame in .458 caliber compared to a 420 gr CEB Raptor. Of course the 500 gr Swift has a Shelf SD of .341 and the 420 Raptor a Shelf SD of only .286. The Manufacturers and Gun Writers would tell you that the higher SD will of course penetrate deeper. But they do not understand, or care to understand what happens when the bullet goes to work, or "Terminal Sectional Density"

1. 500 Swift A Frame 458 Lott 2270 fps Buffalo weight 493 grs Expanded Diameter .824 inches
Terminal Sectional Density .104



Perhaps we should also include a 500 gr Woodleigh Soft in .458, also Shelf SD of .341 as well.

2. 500 Woodleigh Soft 2125 fps Buffalo retained weight 494 gr .902 expanded diameter...... Terminal Sectional Density .087

Apologies for the poor quality photo;



3. 420 CEB Raptor 458 B&M 2250 fps buffalo Retained weight 335 gr maximum terminal diameter (jagged points on front) .465 diameter
Terminal Sectional Density .221





Now we can see how Terminal Sectional Density can at least tell us the story of WHY............

Both of the 500 gr Expanding bullets had less than 1/2 the "Terminal Sectional Density" than what the 420 Raptor retained. In all cases, the 420 Raptor will vastly out penetrate any 500 gr Expanding Conventional bullet, either in test medium, or animal tissue.

500 gr .458 caliber Swift A Terminal SD .104
500 gr .458 caliber Woodleigh Soft Terminal SD .087
420 Raptor Gen II .458 caliber Terminal SD .221

The Terminal Sectional Density can answer the Why as you can see. But people this is simple, you don't have to run the numbers to know this, unless you are just plain STUPID. If you are any sort of knowledgeable shooter, you know that a Swift A Frame will penetrate deeper than a Nosler Ballistic tip, simply by understanding how they are contructed and how they work once Terminals begin. But both the same caliber and same weight on the shelf will have the same SD.

Enter the world of Gen I and Gen II, they work differently than Conventional expanding, and they rock the world of Conventional Thinking.

I could give many many more examples, all to the same point and same end story. Hopefully this opens your eyes somewhat, and helps begin the understanding of Sectional Density, and just what it does mean exactly. For me, not much. I have it in the same category as Muzzle Energy, really only a number but does not mean a lot. There are many many other factors to consider, that are far more important than that of "Shelf SD"..........................

DaddyFlip said:

@IvW gave me an idea how to better illustrate why SD doesn't matter (is not a factor). Consider the following Hornady projectiles - Same "ideal top performing SD for DG of .330"; which one are you choosing for your buffalo hunt? You didn't pick the 416 because of SD, you picked it for (1) energy; (2) diameter; (3) weight. SD never crossed your mind. Even if the 30cal bullet was the same DGX Bonded construction, you wouldn't choose it for your buff hunt because the SD was .330. Even if it were legal, you never considered your 300 H&H for buffalo. SD doesn't matter.

View attachment 770502View attachment 770503

Now if you're choosing between 300-350-400-450 grain bullets for the 416, they will all do the job on buffalo. The heavier the weight, the higher the SD, but that's only a consequence of the weight increasing, not some magical significance of SD. (By the way, every 416 bullet of equal weight has the same SD, regardless of any other metric, making SD even less significant when considering which brand and type of bullet you want to use.)

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It is a factor, an important one, even; just not the only factor.

In a vacuum with no other variables, it doesn't tell us much other than "long/heavy for caliber."

It's a convenient calculation to tell us a characteristic about a given bullet for a given class of animal. Even if the calculation had never been identified, we'd all intuit that a 180 or 200 gr 30 cal is a better choice for elk or moose than a 150 gr. SD is a simple way for us to gain some clarity on our intuition.

All of this science stuff makes me want to give you guys wedgies and swirlies. Maybe duct tape to the flagpole.

SD suggest a bullet's terminal performance is based on a bullets configuration before it touches the game animal. As soon as the bullet enters the animal it usually changes shape and weight and therefore the SD figures change and the SD values for that bullet are instantly rendered useless.
Also, is SD an indication of wound channel, straight line penetration or tissue damage? Usually not SD is yesterday's news.

Gday mark458
Sorry for delayed response I got a little sidetracked on preparations

Mark458 said:

I hope you're elephant hunt goes well and that you drop that big guy in his tracks.

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Thankyou & same

Mark458 said:

I'm very curious about what caliber and bullet weight you have chosen to get a sectional density that low. Would you mind sharing.

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It is a .510 cal shot out of my Jeffery around 2750 MV & is 358 gr

Definitely not one’s normal approach but one that has shown it will preform better than a lot of solids on the market today especially in its ability to resist deflection

Now the final part of this testing will if going well be elephant & that is one I have thought extremely hard on & with the talks /discussions in many parts ( pretty well ever part we could throw @ it ) with a guy I look upto it’s come down to the moment is nearly here & will see if it will do what we expect

That’s about as simple as I can put it for now & also just finishing up which 375 bullet we will take also that is based on a similar concept & one that without a doubt on that you’ll never see me use a 300 gr pill in a 375 again & a 190 to 230 is all that is needed with change I will add on performance compared to any 300 gr or plus pill

Hope that answers some of your curiosity ( I will do a report on the outcome good or bad once hunt is done )

Cheers

I use a light 400 grain bullet in my 50-110 Winchester and it sure kills cape buffalo fast.