Where do you stand on Sectional Density?

Sectional Densities and Ballistic Coefficients are very important on moderate velocity, moderate recoil, deep penetrating calibers like 140gr 6.5x55SE and 175gr 7x57.

For Africa and medium to large bores, it doesn't matter at all. Bullet construction and reliable feed mean virtually everything.

Hunters get themselves into trouble when they apply thinking for 350 yard shots on Pronghorn, 200 yard shots on Elk, and 60 yard shots on Cape Buffalo while smashing together all the things that matter in a universal context.

The mission, the caliber, and the effective average shooting distances determine if SD matters at all.

Read enough from or talk to enough old timers and you will see a trend that the cartridges that hit above their weight almost invariably has a SD of .3 and up.

It's not that SD doesn't matter; it's that the two factors that make up SD matter more and SD does not (and doesn't have to) enter into the everyday conversation of cartridge and bullet selection. If it soothes one to remember "ye olde 0.330", then by all means. My new analogy is this:

Sectional density is the ratio of bullet weight (converted to pounds) divided by bullet diameter squared. The formula is pounds/(inch x inch).

Let's say you have a new sports or muscle car. You proudly proclaim that the car goes 0-60 MPH in 4.8 seconds. The ratio of speed over time is called acceleration, expressed as distance/(time x time). The above 0-60 acceleration (assuming a constant rate) would be 12.5 MPH per second, 18.3 feet/(second x second) or "18.3 feet per second per second". NO ONE talks about nor cares about the acceleration number (sectional density) at the drag strip; all they care about is the time (weight) when the trap speed (caliber) is known. Same for quarter mile; when the distance is known, all we care about is the time. Acceleration is just a calculation that results from the two factors that do matter. There's not even a gauge on the dash for acceleration; you just feel it.

Sectional density is the same. Once you've decided on the caliber (trap speed or distance) , all that matters is the weight (time). If SD really mattered and higher was better, then you could choose any number of unsuitable calibers for DG with SD over .300, such as .308 220 grain or even 6.5mm 160 grain, as I previously demonstrated. Sorry y'all; I get hung up when math is made out to be more important than it is. Proud to say I'm still the only vote for "It doesn't matter at all".

Sectional density is a differentiating factor only if all other factors are equal (which seldom occurs in practice).

DaddyFlip said:

It's not that SD doesn't matter; it's that the two factors that make up SD matter more and SD does not (and doesn't have to) enter into the everyday conversation of cartridge and bullet selection. If it soothes one to remember "ye olde 0.330", then by all means. My new analogy is this:

Sectional density is the ratio of bullet weight (converted to pounds) divided by bullet diameter squared. The formula is pounds/(inch x inch).

Let's say you have a new sports or muscle car. You proudly proclaim that the car goes 0-60 MPH in 4.8 seconds. The ratio of speed over time is called acceleration, expressed as distance/(time x time). The above 0-60 acceleration (assuming a constant rate) would be 12.5 MPH per second, 18.3 feet/(second x second) or "18.3 feet per second per second". NO ONE talks about nor cares about the acceleration number (sectional density) at the drag strip; all they care about is the time (weight) when the trap speed (caliber) is known. Same for quarter mile; when the distance is known, all we care about is the time. Acceleration is just a calculation that results from the two factors that do matter. There's not even a gauge on the dash for acceleration; you just feel it.

Sectional density is the same. Once you've decided on the caliber (trap speed or distance) , all that matters is the weight (time). If SD really mattered and higher was better, then you could choose any number of unsuitable calibers for DG with SD over .300, such as .308 220 grain or even 6.5mm 160 grain, as I previously demonstrated. Sorry y'all; I get hung up when math is made out to be more important than it is. Proud to say I'm still the only vote for "It doesn't matter at all".

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I'm curious what is your dangerous game caliber of choice, in this case let's say for buffalo, and what grain bullet do you shoot.

DaddyFlip said:

It's not that SD doesn't matter; it's that the two factors that make up SD matter more and SD does not (and doesn't have to) enter into the everyday conversation of cartridge and bullet selection. If it soothes one to remember "ye olde 0.330", then by all means. My new analogy is this:

Sectional density is the ratio of bullet weight (converted to pounds) divided by bullet diameter squared. The formula is pounds/(inch x inch).

Let's say you have a new sports or muscle car. You proudly proclaim that the car goes 0-60 MPH in 4.8 seconds. The ratio of speed over time is called acceleration, expressed as distance/(time x time). The above 0-60 acceleration (assuming a constant rate) would be 12.5 MPH per second, 18.3 feet/(second x second) or "18.3 feet per second per second". NO ONE talks about nor cares about the acceleration number (sectional density) at the drag strip; all they care about is the time (weight) when the trap speed (caliber) is known. Same for quarter mile; when the distance is known, all we care about is the time. Acceleration is just a calculation that results from the two factors that do matter. There's not even a gauge on the dash for acceleration; you just feel it.

Sectional density is the same. Once you've decided on the caliber (trap speed or distance) , all that matters is the weight (time). If SD really mattered and higher was better, then you could choose any number of unsuitable calibers for DG with SD over .300, such as .308 220 grain or even 6.5mm 160 grain, as I previously demonstrated. Sorry y'all; I get hung up when math is made out to be more important than it is. Proud to say I'm still the only vote for "It doesn't matter at all".

Click to expand...

This is what I was trying to say and you’ve done a far better job than I did.
All 300 grain 375 bullets will have the exact same sectional density, every last one. A 300 grain sierra will act differently than a Swift that will act differently than a Barnes banded solid, yet the SD is the same for all.
As an indicator of bullet performance, SD is far down the list.

Mark458 said:

I'm curious what is your dangerous game caliber of choice, in this case let's say for buffalo, and what grain bullet do you shoot.

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If you have stumbled upon several of my other posts, you'll know I don't hunt and I won't ever go to Africa. Ballistic theory and mathematics, which we are investigating here, are immune to such practical limitations. However, were you to drag me to Africa, I could bring either 375H&H or 416Rem, for which I have 270-300gr and 350-400gr bullets, respectively, of various styles. Either caliber in either grain would suit, though the heavier bullet in both calibers might offer better insurance (all other factors equal) because they are heavier; the resulting SD is merely a mathematical consequence.

The only point I've been trying to make, and my answer to the OP question, is illustrated in bold below. For DG, of the three numbers listed, SD is the LEAST important. If such a wide range of caliber and bullet weights can have the same "ideal for DG" SD, then it must be ruled out as an important factor. The caliber and weight, the energy the combination produces, and the bullet type are all more important than the SD number. After those (or maybe before all of those), it's with what total combination the shooter can reliably hit the target.

Cal-Grs (SD)
375-270 (.274)
416-350 (.289)
375-300 (.305)
416-400 (.330)
308-220 (.331)
264-160 (.328)

I dont think SD is important until you start getting into larger caliber and hence larger game. I hunted deer and elk primarily. A good 150g bullet and up will take either of these easily without worrying about SD.

As I have posted elsewhere, SD shows the average length of a bullet (given similar density). The measurement is weight/diameter x diameter. DxD would be the frontal area of a square bullet. Actual area would be Pi x radius x radius. but since both methods are proportional, both work. In either case the result is weight/area. The answers will get larger as the weight increases and smaller as the area increases. If the bullet shape was flat point and base with parallel sides- shaped like a wad-cutter all bullets with similar SDs would be the same length regardless of diameter. A better criteria would be the ratio of bullet length to diameter.

DaddyFlip said:

you'll know I don't hunt and I won't ever go to Africa. Ballistic theory and mathematics, which we are investigating here, are immune to such practical limitations.

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nough said......

IvW said:

SD is tops for DG ideal top performing SD is around .330 or slightly more

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No need to cast aspersions. Would you hunt DG with a 7mm Rem Mag, 190gr. match bullet with SD of .337?

If not, SD is not tops for DG or any G...

IvW said:

nough said......

Click to expand...

DaddyFlip said:

If you have stumbled upon several of my other posts, you'll know I don't hunt and I won't ever go to Africa. Ballistic theory and mathematics, which we are investigating here, are immune to such practical limitations. However, were you to drag me to Africa, I could bring either 375H&H or 416Rem, for which I have 270-300gr and 350-400gr bullets, respectively, of various styles. Either caliber in either grain would suit, though the heavier bullet in both calibers might offer better insurance (all other factors equal) because they are heavier; the resulting SD is merely a mathematical consequence.

The only point I've been trying to make, and my answer to the OP question, is illustrated in bold below. For DG, of the three numbers listed, SD is the LEAST important. If such a wide range of caliber and bullet weights can have the same "ideal for DG" SD, then it must be ruled out as an important factor. The caliber and weight, the energy the combination produces, and the bullet type are all more important than the SD number. After those (or maybe before all of those), it's with what total combination the shooter can reliably hit the target.

Cal-Grs (SD)
375-270 (.274)
416-350 (.289)
375-300 (.305)
416-400 (.330)
308-220 (.331)
264-160 (.328)

Click to expand...

I don't think we disagree as much as you think we do. You said it yourself, the heavier bullet in each caliber would most likely offer better insurance all other factors being equal. That's been my argument from the start. I don't seek out high sectional density as much as I just happen to end up there.

The insurance analogy is a good one. A standard insurance policy is choosing standard for caliber bullet weights. 300 Grain for 375. 400 Grain for 416 and 500 Grain for 458. The sectional density you end up with is generally on the north side of .3. I know bullets are much better than they used to be but when you go light for caliber I feel you are choosing to go without any insurance. It might work the vast majority of the time, but sooner or later you may need that insurance. This isn't just my gut feeling, as I mentioned earlier I have talked with different PH'S over the past 25 years who have experienced it first hand with clients that shoot 250 or 270 grain bullets from their 375's and have run into trouble even with high quality bullets. I feel the mistake many of these hunters are making is that they want one rifle that will take care of all their needs while on safari and choose the flatter shooting option. While I often have taken just one rifle I never compromise the buffalo hunt by shooting a lighter bullet to help with my plains game hunting. I practice shooting longer distances with the heavier bullets.

Going heavy for caliber in my opinion is like taking a rider on your insurance policy. Good chance you won't need it, but it's there if you do. The additional price for this is a little bit of velocity. I think the price is cheap.

Again I don't seek out high sectional density as the most important factor in bullet selection. By not choosing light for caliber bullets I just happen to end up with a relatively high sectional density.

Mark458 said:

Sectional density is merely an indicator of momentum which translates to penetration. If you're hunting dangerous game and you want maximum penetration then you are going to choose the heaviest bullets within the chosen caliber which in turn is going to have the highest sectional density.

The chart shown above shows the same sectional density of two different calibers. Obviously the larger caliber is going to inflict more damage to the animal. A better choice of charts would compare a range of calibers that you would choose from to hunt dangerous game. 375 H&H to let's say 505 Gibbs to keep it within reasonable choices.

A few examples of these are

Caliber. Weight. SD

.375 350. .356
.416. 430. .355
.458. 550 .375
.505. 600. .330

Notice that these are all heavy for caliber options.

You can see that the 375 caliber at 350 grains has a SD significantly higher than the 505 Gibbs. It may very well penetrate better than the Gibbs. Is there anyone on this forum that is willing to argue that the 375 is going to do more damage than the Gibbs given they are utilizing the same bullet (let's say a Swift A Frame)

The one that stood out to me was the 458. That has been my caliber of choice for some time now. It has the best SD and is a large diameter. The best possible penetration while inflicting a large wound channel.

Let the debate continue.

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Sectional density is an indicator of momentum????? Please explain

375 Ruger Fan said:

Sectional density is an indicator of momentum????? Please explain

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Great discussion.
What about SD when the bullet is penetrating the target medium?
Mono metal, bonded, or cup and core?

Reference from Pierre van der Walt, African Dangerous Game Cartridges.

Indicator of momentum retention is slightly different and I totally agree with that statement.

Momentum has a velocity component. SD does not. So how one is an indicator of the other is a bit of a stretch.

375 Ruger Fan said:

Indicator of momentum retention is slightly different and I totally agree with that statement.

Momentum has a velocity component. SD does not. So how one is an indicator of the other is a bit of a stretch.

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You're correct, I left out the word retention in my earlier post when talking about penetration potential

Mark458 said:

I don't think we disagree as much as you think we do. You said it yourself, the heavier bullet in each caliber would most likely offer better insurance all other factors being equal. That's been my argument from the start. I don't seek out high sectional density as much as I just happen to end up there.

The insurance analogy is a good one. A standard insurance policy is choosing standard for caliber bullet weights. 300 Grain for 375. 400 Grain for 416 and 500 Grain for 458. The sectional density you end up with is generally on the north side of .3. I know bullets are much better than they used to be but when you go light for caliber I feel you are choosing to go without any insurance. It might work the vast majority of the time, but sooner or later you may need that insurance. This isn't just my gut feeling, as I mentioned earlier I have talked with different PH'S over the past 25 years who have experienced it first hand with clients that shoot 250 or 270 grain bullets from their 375's and have run into trouble even with high quality bullets. I feel the mistake many of these hunters are making is that they want one rifle that will take care of all their needs while on safari and choose the flatter shooting option. While I often have taken just one rifle I never compromise the buffalo hunt by shooting a lighter bullet to help with my plains game hunting. I practice shooting longer distances with the heavier bullets.

Going heavy for caliber in my opinion is like taking a rider on your insurance policy. Good chance you won't need it, but it's there if you do. The additional price for this is a little bit of velocity. I think the price is cheap.

Again I don't seek out high sectional density as the most important factor in bullet selection. By not choosing light for caliber bullets I just happen to end up with a relatively high sectional density.

Click to expand...

I agree with all of this.

A Well Constructed Bullet + Good Sectional Density (generally) = Deep Straight Line Penetration.

Which diameter bullet is appropriate for Antelope or Buffalo is another conversation.

Wyatt Smith said:

This is what I was trying to say and you’ve done a far better job than I did.
All 300 grain 375 bullets will have the exact same sectional density, every last one. A 300 grain sierra will act differently than a Swift that will act differently than a Barnes banded solid, yet the SD is the same for all.
As an indicator of bullet performance, SD is far down the list.

Click to expand...

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.