Sectional Density

[PLThomas]

I’m a little confused when it comes to sectional density and revolver calibers for defense against predators or even hunting.

From my understanding, the smaller the diameter bullet will have a higher sectional density (given the bullet weights are the same).

So why does everyone suggest a larger caliber for defense against predators or hunting if a smaller caliber with a higher sectional density is considered inadequate? for example I have had many people tell me that a 45 colt (standard pressure not the hot loaded stuff) 10mm, 44 special etc. is a better round for hunting or predator defense than a .357 magnum.

sectional density for a 180 gr .357 mag is ~.202, for a 200gr it’s ~.224.

for a 255 gr .45 colt it’s ~.178, .44 special 246gr ~.191, and 10mm 220gr is ~.196.

the .357 magnum has a higher SD and in a lot of cases also has a higher velocity and muzzle energy, so it would seem that it would be the better round, yet I always hear “get the largest caliber you can shoot accurately”. (Obviously I’m not comparing .357 mag to .41 mag, .44 mag or any of the larger magnum/super magnum calibers).


sorry for the long post, just trying to learn and understand how this all comes into play.

 

[J-Bar]

Non-ballistician here.

I think sectional density is important when shooting at long range. SD helps the bullet retain velocity and punch through wind efficiently.

At short range a big hole is more likely to take down a threat quickly.

I’m sure others can provide details more eloquently than I.

 

[PLThomas]

Non-ballistician here.

I think sectional density is important when shooting at long range. SD helps the bullet retain velocity and punch through wind efficiently.

At short range a big hole is more likely to take down a threat quickly.

I’m sure others can provide details more eloquently than I.

So would that mean that a light for caliber bullet in .45 would be better than a heavy for caliber .357 just due to the diameter? Let’s say a 185gr .45 vs 180gr or 200gr .357?

Light for caliber on the .45 in order to get velocity up, or would a standard weight still be better even if it had lower velocity?

 

[mcb]

IMHO SD is not a great number for much of anything. For external ballistics high SD is good for long range but Ballistic Coefficient tells the story better. For terminal ballistics (unless we are talking about bullets that do not deform) SD starts changing, usually decreasing rapidly, as soon as the bullet hits the target and starts to expand.

 

[PLThomas]

IMHO SD is not a great number for much of anything. For external ballistics high SD is good for long range but Ballistic Coefficient tells the story better. For terminal ballistics (unless we are talking about bullets that do not deform) SD starts changing, usually decreasing rapidly, as soon as the bullet hits the target and starts to expand.

Are expanding bullets better for predator defense? I was always under the impression that you wanted a hard cast/non deforming bullet for that job.

 

[DR505]

Are expanding bullets better for predator defense? I was always under the impression that you wanted a hard cast/non deforming bullet for that job.

"Predator" covers a lot of ground.

 

[earplug]

I don't think sectional density is much of a issue with handgun caliber bullets. Your dealing with relatively short chambers and magazines. Mass is perhaps the best a handgun can rely on. Witness the great penetration of old 44 and 45 caliber handgun bullets.

 

[mcb]

Are expanding bullets better for predator defense? I was always under the impression that you wanted a hard cast/non deforming bullet for that job.

Whether you use an expanding bullet vs a non-expending bullet is all about balancing penetration and damage. Getting sufficient penetration is number one priority with damage a close second. Expending bullets typically give up some penetration to increase the damage. So now you must look at your potential target and balance that against the capabilities of your selected handgun and choose ammo that will give you sufficient penetration while hopefully maximizing damage. Too much pentation gives up potential damage and insufficient pentation means your damage might not get to where it is needed to kill the target.

 

[Riomouse911]

Handguns don’t drive bullets at rifle velocities that allow for large expansion along with deep penetration to kill. Expansion limits penetration, especially at the lower velocities handguns generate.

Big bore SWC type handgun bullets striking a critter at a .410”, .429” or .452”,etc. diameter are already near the size of an expanded .358” bullet, so you’ll get deep penetration from the mass and good damage potential with a larger diameter magnum handgun bullet than a smaller one.

Stay safe.

 

[PLThomas]

Handguns don’t drive bullets at rifle velocities that allow for large expansion along with deep penetration to kill. Expansion limits penetration, especially at the lower velocities handguns generate.

Big bore SWC type handgun bullets striking a critter at a .410”, .429” or .452”,etc. diameter are already near the size of an expanded .358” bullet, so you’ll get deep penetration from the mass and good damage potential with a larger diameter magnum handgun bullet than a smaller one.

Stay safe.

That makes a lot of sense, thank you

 

[jmr40]

I think sectional density is important when shooting at long range. SD helps the bullet retain velocity and punch through wind efficiently.

At short range a big hole is more likely to take down a threat quickly.

You're confusing Ballistic Coefficient "BC" with sectional density "SD". Although often the best BC is also an indication of a high SD, but not always. Bullets with a higher SD will penetrate deeper than those with low SD numbers (all other factors being the same). High BC bullets are more aerodynamic and retain speed better at range.

And a small hole that penetrates to vital organs does far more damage than a big hole that doesn't make it to the vital organs.

But this isn't a simple concept to explain. And to be honest is more relevant to rifles than handguns. SD is a ratio of a bullets weight and diameter. For example a 147 gr 9mm bullet will penetrate much deeper than a 155 or even 165 gr 40 caliber bullet. Once you get to 180 or 200 gr 40 caliber bullets then penetration starts to equal out.

And it assumes the same bullet construction and the same impact speeds. Some bullets expand rapidly at relatively slow speed and don't penetrate well even with high SD numbers. Other bullet designs penetrate very deep. And impact speed limits penetration. There are entire books dedicated to the topic. But SD is a factor, but not the only one to consider.

A general rule is to use heavy for caliber bullets if you need deep penetration. And a heavy for caliber 9mm or .357 caliber bullet will out penetrate a light for caliber 40 or 45 caliber bullet.

 

[WrongHanded]

Meplat diameter and velocity are probably more important than bullet diameter or section density. Section density does help conserve momentum though.

 

[wcwhitey]

Handguns don’t drive bullets at rifle velocities that allow for large expansion along with deep penetration to kill. Expansion limits penetration, especially at the lower velocities handguns generate.

Big bore SWC type handgun bullets striking a critter at a .410”, .429” or .452”,etc. diameter are already near the size of an expanded .358” bullet, so you’ll get deep penetration from the mass and good damage potential with a larger diameter magnum handgun bullet than a smaller one.

Stay safe.

Right on the money.

 

[PLThomas]

So a large diameter heavy bullet (250+ gr .45) will do better in penetration even if it has a lower velocity (say 800 fps) vs something like a 180gr or 200gr .357 mag going much faster? Is this all due to the larger bullet mass retaining momentum longer?

I guess what I am asking now is how much does velocity come into play. Is there a known point where a large caliber heavy bullet is just going too slow to penetrate?

 

[WrongHanded]

So a large diameter heavy bullet (250+ gr .45) will do better in penetration even if it has a lower velocity (say 800 fps) vs something like a 180gr or 200gr .357 mag going much faster? Is this all due to the larger bullet mass retaining momentum longer?

I guess what I am asking now is how much does velocity come into play. Is there a known point where a large caliber heavy bullet is just going too slow to penetrate?

There's a big difference between penetration depth and wound damage. That doesn't answer your question, but it's worth mentioning.

 

[wcwhitey]

So a large diameter heavy bullet (250+ gr .45) will do better in penetration even if it has a lower velocity (say 800 fps) vs something like a 180gr or 200gr .357 mag going much faster? Is this all due to the larger bullet mass retaining momentum longer?

I guess what I am asking now is how much does velocity come into play. Is there a known point where a large caliber heavy bullet is just going too slow to penetrate?

Its mass will better help it overcome things like bone. It’s wound channel .452 SWC vs .357 SWC is already bigger. Hard cast bullets at anything 800 fps and faster will penetrate more than what is needed on soft tissue (ballistic gel). It’s when they strike objects like bone when mass becomes more important. The bigger the animal the more dense muscles and bones you will encounter.

Now if all you have is a .357 and heavy game and predators are your concern. Nothing wrong with a 180 Grain Flat Nosed Hard Cast Bullet at 1100 FPS out of a Trail Gun.

 

[PLThomas]

"Predator" covers a lot of ground.

When I say predators I am talking about if these calibers were to be used against something like a Cougar, Black Bear, Grizzly Bear or Moose. Obviously I know there are better choices for large, dangerous game (such as .44 mag or bigger) but I have had people tell me that a .45 acp is better vs a cougar or black bear than a .357 mag because the .45 is bigger and heavier and I’m just trying to figure out why.

I would have guessed a 180-200gr hard cast .357 mag going ~1300fps would be better than a 230-255gr .45 acp going ~900fps. But it sounds like the consensus is that larger and heavier is always better as long as it hits the intended target.

 

[wcwhitey]

When I say predators I am talking about if these calibers were to be used against something like a Cougar, Black Bear, Grizzly Bear or Moose. Obviously I know there are better choices for large, dangerous game (such as .44 mag or bigger) but I have had people tell me that a .45 acp is better vs a cougar or black bear than a .357 mag because the .45 is bigger and heavier and I’m just trying to figure out why.

I would have guessed a 180-200gr hard cast .357 mag going ~1300fps would be better than a 230-255gr .45 acp going ~900fps. But it sounds like the consensus is that larger and heavier is always better as long as it hits the intended target.

I think you are correct. I would rather have that .357 with a hard cast, semi Wadcutter gas check with the flattest nose it could have over a .45 ACP with hollow points or FMJ.

Edit: If it was me though I would not choose between those two. In the Lower 48 I would be be just fine with a .44 Special 260 SWC Wide Nosed at 900 FPS.

 

[PLThomas]

Okay, BTW thank you everyone for the replies.

 

[WrongHanded]

So again, meplat diameter and velocity are the important factors in wounding with non-expanding handgun projectiles.



Increasing bullet diameter and weight can certainly increase penetration depth. But as with defensive ammunition for human threats, only so much penetration is required. The degree of wounding done to that depth of penetration however, is important.

 

[StrawHat]

The ballisticians figured this out long ago. The best cartridge, bullet weight combination was usually the only offering. But then, experimenters, designers and hunters got involved. And that brought us choices. Not a bad thing just a confusing thing.

But when it gets too boggling, you can always return to the standard bullet weights and be well served.

Kevin

 

[CraigC]

Sectional density is a good predictor of penetration. One can reasonably assume that bullets of similar SD and design will offer similar penetration. It's also a useful tool when comparing one caliber to another. Wanna know what .45 bullet will penetrate similarly to your favorite .475 bullet? SD is the answer. For non-expanding hardcast bullets, the sweet spot seems to be .25 - .27. Here we find bullets in the 355-360gr range for .44's and .45's, 430's in .475 and 440-500gr for .500's. These will penetrate nearly double that of "standard" weight bullets like the .44cal 250gr Keith bullet. Shape is also critically important. Larger meplats cause more tissue destruction but lose a little penetration. Even so, I prefer WFN's and WLN's over LFN's. A bullet that 'looks' like an LBT but isn't, might not penetrate worth a crap. We've seen that first hand.

The problem with comparing the big bores to smaller cartridges like the .357 is that the .357 really needs expansion to be effective. The .44 and bigger do not. In fact, except for light game like deer, we'd usually rather they didn't. To answer your question, yes, a 200gr .357 hardcast will penetrate better than a 250-260gr .45 bullet, at the expense of wounding.

 

[bangswitch]

Sectional density has to do with the bullet weight for its diameter. Small diameter may penetrate better than large diameter, but that is dependent on bullet weight as well. Velocity at impact being the same, a heavy-for-diameter bullet will penetrate deeper than a lighter-for-diameter one of the same diameter. SD pays a part in bullet stability as well, as a heavy bullet has to be longer than a lighter bullet when they are both the same diameter, and a longer bullet will be more stable in flight. Shape plays an additional role, which can also determine length. Boat-tail bullets fly better than flat-tail ones (less drag), and a highly tapered ogive flies better than a rounded one.

 

[buck460XVR]

When I say predators I am talking about if these calibers were to be used against something like a Cougar, Black Bear, Grizzly Bear or Moose.

Never really considered moose as a predator, even tho they injure 5-10 folks a year in Alaska....more than Grizzly and Black bear attacks combined. Just a thick skinned, heavily muscled game animal. Most common predator around here are coyotes. Thin skinned and easy to kill. I generally kill at least one a year while turkey hunting with a shotgun. Same can be said for wolves, bobcats and cougars. No real need for bone crushing penetration. Good percentage of Dangerous Game animals are like Moose, not predators, but large herbivore prey animals that have learned and evolved, to protect themselves and their offspring, from predators.

While SD can be somewhat of a predictor of penetration, the actual construction of the projectile is just as important, especially when it comes to jacketed bullets, but also affects lead and other monolithics.

I’m a little confused when it comes to sectional density and revolver calibers for defense against predators or even hunting.

Because of their relative short effective range, I pay little or no attention to the SD of my revolver hunting bullets, even those used in my handgun caliber carbines. I use projectiles that exhibit the best accuracy, while providing the type of terminal performance I want. Bullet construction for the most part, when we talk about revolvers, is the major contributor to terminal performance, whether it be expansion or penetration.

 

[BobWright]

Sectional density vs. mass. Mass wins.

Bob Wright