Sectional Density

[WrongHanded]

Sectional density vs. mass. Mass wins.

Bob Wright

That depends on how the mass is distributed. A silver dollar probably won't get great penetration.

 

[BobWright]

That depends on how the mass is distributed. A silver dollar probably won't get great penetration.

That depends on the velocity.

Bob Wright

 

[WrongHanded]

That depends on the velocity.

Bob Wright

It sure does Bob. Velocity can help overcome lower sectional density.

 

[mcb]

For a given velocity a silver dollar that hits edge on is going to penetrate allot better that one that hits flat.

 

[CraigC]

Velocity is far less important than mass.

I've heard the same people that advocate "heavy for caliber" bullets say that SD is meaningless. I reckon they didn't understand it in the first place.

 

[WrongHanded]

For a given velocity a silver dollar that hits edge on is going to penetrate allot better that one that hits flat.

Yep. Neither will penetrate as well as the same material made into a ball, and that won't penetrate as well as the material made into a cylinder (striking end on) that is twice as long as its diameter is wide.

 

[WrongHanded]

Velocity is far less important than mass.

For penetration, or for wounding?

 

[CraigC]

IMHO, velocity will have a greater impact on wounding than penetration. In fact, it can be detrimental to penetration, depending on the bullet. Maybe this year I'll finally do the testing that will bear this out.

 

[JTQ]

You're confusing Ballistic Coefficient "BC" with sectional density "SD".

I believe this is correct.

 

[WrongHanded]

IMHO, velocity will have a greater impact on wounding than penetration. In fact, it can be detrimental to penetration, depending on the bullet. Maybe this year I'll finally do the testing that will bear this out.

This is exactly what Veral Smith of Lead Bullet Technologies says in Chapter 17 ('Stopping Power Formulas') of his book Jacketed Performance With Cast Bullets. Which is where I pulled the image from that I used in post #20. If you haven't read it, you should consider doing so. It's exactly your sort of thing.

 

[CraigC]

This is exactly what Veral Smith of Lead Bullet Technologies says in Chapter 17 ('Stopping Power Formulas') of his book Jacketed Performance With Cast Bullets. Which is where I pulled the image from that I used in post #20. If you haven't read it, you should consider doing so. It's exactly your sort of thing.

I've got his book somewhere here. IMHO, he's 100% correct. He effectively disproved the myth that the legendary Keith bullet made use of its cutting shoulder in tissue. When in fact, it had no effect at all. The meplat was doing all the work. That picture illustrates how it creates the wound channel and why it's typically a good bit larger than the bullet itself. The SWC just makes nice holes in paper. I've heard people claim that cast bullets only make a hole the diameter of the bullet. In fact, I have a picture of a deer's heart with one big chunk of it removed as the .476" 355gr WFN passed through. They kill all out of proportion to their paper ballistics.

 

[JTQ]

That depends on how the mass is distributed. A silver dollar probably won't get great penetration.

That depends on the velocity.

Bob Wright

 

[WrongHanded]

I've got his book somewhere here. IMHO, he's 100% correct. He effectively disproved the myth that the legendary Keith bullet made use of its cutting shoulder in tissue. When in fact, it had no effect at all. The meplat was doing all the work. That picture illustrates how it creates the wound channel and why it's typically a good bit larger than the bullet itself. The SWC just makes nice holes in paper. I've heard people claim that cast bullets only make a hole the diameter of the bullet. In fact, I have a picture of a deer's heart with one big chunk of it removed as the .476" 355gr WFN passed through. They kill all out of proportion to their paper ballistics.

The chart also shows that a 38(.357) FN driven at 1200fps creates a larger would diameter than a .44 WFN driven to 900fps.

In that chapter he talks about concepts such as Displacement Velocity (DV) of tissue off of the meplat, and of Terminal Sectional Density (TSD) which is calculated based on the meplat diameter rather than bullet diameter, because as you mentioned, only the flat nose of the bullet is actually doing the work. And he talks about balancing the TSD and DV to get best results.

I suppose one could approach his work with skepticism, but the concepts he's written about line up so well with the real world information coming from big bore handgun hunters like you, it's hard to argue with his work.

 

[Mycin]

I've been researching this sort of stuff on and off for decades, even more-so recently in considering whether my 357 or 45 Blackhawk would be most appropriate for hogs. For a while, I had the same question as the OP -- why isn't a 357 bullet of similar SD yet higher velocity considered in the same class as a 44 or 45 of lower velocity? The consensus among experienced handgun hunters is that they aren't, but why? Here's how I look at the issue.

Meplat diameter and velocity determine the diameter of the wound channel - bullet mass/sectional density don't matter at a superficial level. However, velocity is an ever-decreasing value, especially in terminal ballistics. More mass means more momentum, which helps retain velocity as the bullet passes through bone and tissue so that the wound channel is still significant when passing through vitals. That's where higher BC comes in - retaining more velocity.

One of the concerns in terminal ballistics is that the bullet be able to punch through tough hide and bone and not be slowed or deflected so much that the vitals aren't hit. A 1" thick bone is nearly three times as thick as a 357 bullet is wide, whereas it's slightly over twice as thick as a 45 bullet is wide. In other words, a given bone is less of an obstruction to the bigger bullet, relatively speaking. Same for thick hide and dense muscle. When this idea finally sunk into my brain, it all started to make more sense.

I think of it sort of like weight classes in boxing. A welter weight fighter of great skill is unlikely to knock out a mediocre heavy weight boxer, simply due to the difference in mass.

So my 357 would be fine for light bodied game such as deer, and even for smaller hogs, but big tough hogs, bears, elk, moose, etc., are really out its weight class.

 

[black mamba]

In hunting, penetration is king. You must reach the vitals, and the perfect broadside shot is not always available, so you need enough penetration to get through tough hide and bone. Since a small hole through the vitals is better than a large wound through non-vital tissue, penetration trumps wound mass. SD not only helps penetration, but it adds punch and shock to the target animal. I always use heavy for caliber bullets for hunting (300s to 340s in .45, 265s to 300s in .44, and 225s to 250s in .41).

 

[CraigC]

The chart also shows that a 38(.357) FN driven at 1200fps creates a larger would diameter than a .44 WFN driven to 900fps.

In that chapter he talks about concepts such as Displacement Velocity (DV) of tissue off of the meplat, and of Terminal Sectional Density (TSD) which is calculated based on the meplat diameter rather than bullet diameter, because as you mentioned, only the flat nose of the bullet is actually doing the work. And he talks about balancing the TSD and DV to get best results.

I suppose one could approach his work with skepticism, but the concepts he's written about line up so well with the real world information coming from big bore handgun hunters like you, it's hard to argue with his work.

This is why I despise the oft-repeated notion that all you need is a standard weight bullet at 900fps. Elmer Keith figured out nearly 100yrs ago that his 1200fps load killed better than 900fps. Now, 900fps is effective but I can't agree with the idea that more isn't better. The problem you run into with cast bullets is that the faster you push them, the more you risk deformation. Good for wound channel width, bad for depth.

The testing I want to do is to determine what role velocity plays in penetration with a bullet that does not deform.

 

[WrongHanded]

Hey OP! Are you confused yet?

I would suggest that if you want to learn a little more, you consider contacting Lead Bullet Technology and getting a copy of the book I mentioned earlier. I actually had to talk to Veral by phone to get a copy, but he seems like a very smart guy. I had a good conversation with him. He came up with the WFN, LFN and WLN designs when the Keith style SWC was consider the king of non-expanding bullet designs. If you get him on the phone, he may even answer some of your questions. And if you ever decided later that you wanted to cast your own, that info is all on the book.

 

[PLThomas]

Hey OP! Are you confused yet?

I would suggest that if you want to learn a little more, you consider contacting Lead Bullet Technology and getting a copy of the book I mentioned earlier. I actually had to talk to Veral by phone to get a copy, but he seems like a very smart guy. I had a good conversation with him. He came up with the WFN, LFN and WLN designs when the Keith style SWC was consider the king of non-expanding bullet designs. If you get him on the phone, he may even answer some of your questions. And if you ever decided later that you wanted to cast your own, that info is all on the book.

I would say not so much confused but more intrigued, I have been looking up information on Veral Smith’s book and his formulas for calculating penetration and I think I definitely want to get a copy of his book.

quick question for someone who has the book, In this article: https://alaskagunsite.wordpress.com/2017/01/01/the-case-for-the-357-magnum/

the author quotes a formula for calculating potential/forecasted penetration, he states:

“We can easily turn this into a forecasted penetration (+/- 5%) of aqueous animal tissue or 10% ballistic gelatin by using the following formula: 28.8 X (.400″/.280″) X 1.3 = 53.5 inches of penetration (PEN) If you’re wondering what that .280″ number is, this is the typical meplat diameter of a factory loaded 44 caliber bullet that has a flat-nose. (All bullets in these comparisons are hard-cast bullets with wide meplats….just what the doctor ordered for unruly Brown Bears!) The 1.3 number is a coefficient for human tissue or 10% ballistic gelatin. Wood or water or other mediums would have different coefficients.”

I am assuming the formula is from Veral Smith as he is talking about his formulas, but what I don’t understand is where the .400” number comes from.

*and once again, thank you for all the info and replies, everyone has been extremely helpful!

 

[WrongHanded]

The testing I want to do is to determine what role velocity plays in penetration with a bullet that does not deform.

I will be very interested in those results, Craig!

I also believe maintaining meplat integrity is very important. And I can completely understand why increasing velocity can be detrimental. The relatively new popularity of mono solids such as copper (even with reduced mass for volume) seem to address this well. But I'm betting your testing will reveal the truth of the matter.

Reading through that book has really opened my eyes on the effectiveness of the typical 10mm bullet design for woods defense vs .357 mag. The 10mm is just much more of a compromise due to the necessities of bullet profile on an auto-loading cartridge design.

And I've also come to the conclusion that for my own purposes, 1200fps is an effective velocity to maintain. If that were to remain a constant, both penetration and wounding can be increased through meplat diameter and mass. But that's just me, and for your purposes (hunting very large game), I can see why you might feel differently.

 

[WrongHanded]

I would say not so much confused but more intrigued, I have been looking up information on Veral Smith’s book and his formulas for calculating penetration and I think I definitely want to get a copy of his book.

quick question for someone who has the book, In this article: https://alaskagunsite.wordpress.com/2017/01/01/the-case-for-the-357-magnum/

the author quotes a formula for calculating potential/forecasted penetration, he states:

“We can easily turn this into a forecasted penetration (+/- 5%) of aqueous animal tissue or 10% ballistic gelatin by using the following formula: 28.8 X (.400″/.280″) X 1.3 = 53.5 inches of penetration (PEN) If you’re wondering what that .280″ number is, this is the typical meplat diameter of a factory loaded 44 caliber bullet that has a flat-nose. (All bullets in these comparisons are hard-cast bullets with wide meplats….just what the doctor ordered for unruly Brown Bears!) The 1.3 number is a coefficient for human tissue or 10% ballistic gelatin. Wood or water or other mediums would have different coefficients.”

I am assuming the formula is from Veral Smith as he is talking about his formulas, but what I don’t understand is where the .400” number comes from.

*and once again, thank you for all the info and replies, everyone has been extremely helpful!

I'm not sure the PEN formula is Veral's. From reading his work it seems he values full penetration on game animals, so I can see why he'd feel the need to calculate penetration depth.

But - that article got me very interested - I did the math myself for the various results posted. Using the .400" in the PEN formula, and the 400fps in the PWC formula, as constants. And as constants, they work out to the same results. So either they actually are constants. Or the math is all funky and wrong because the author has used those values as constants when they in fact are not. The former seems more likely.

I'm going to record these formulas now, and run so.e of my own loads with them.

 

[Mycin]

FWIW, Bear Tooth Bullets used to have a cavitation calculator on their web site (before they closed down) that calculated cavitation in wetpack (IIRC) based on meplat diameter and velocity. Out of curiosity, I reverse-engineered their results and found that the formula they used was (Velocity) * (Meplat Diameter) / 400. There's that number again. There must be something out there that these various sources are referencing to get that constant.

 

[PLThomas]

I'm not sure the PEN formula is Veral's. From reading his work it seems he values full penetration on game animals, so I can see why he'd feel the need to calculate penetration depth.

But - that article got me very interested - I did the math myself for the various results posted. Using the .400" in the PEN formula, and the 400fps in the PWC formula, as constants. And as constants, they work out to the same results. So either they actually are constants. Or the math is all funky and wrong because the author has used those values as constants when they in fact are not. The former seems more likely.

I'm going to record these formulas now, and run so.e of my own loads with them.

The only problem I have ran into with .400 being a constant is if you have a Meplat larger than .400 (such as a full wadcutter .41, .44 or .45) the penetration depths are very small compared to something with a smaller meplat.

maybe that is correct, but looking at Smith’s displacement velocity formula, a full wadcutter bullet will give you the best results per caliber if velocity is the same (I.e. a full wadcutter .45 at 1000fps is going to have a higher Displacement Velocity than a semi wadcutter or round flat nose going the same speed)

I would think that something that has a DV in the 100-125 range that he states would also have a similar penetration depth as a different bullet in the same DV range. I could be completely wrong here.

 

[WrongHanded]

The only problem I have ran into with .400 being a constant is if you have a Meplat larger than .400 (such as a full wadcutter .41, .44 or .45) the penetration depths are very small compared to something with a smaller meplat.

maybe that is correct, but looking at Smith’s displacement velocity formula, a full wadcutter bullet will give you the best results per caliber if velocity is the same (I.e. a full wadcutter .45 at 1000fps is going to have a higher Displacement Velocity than a semi wadcutter or round flat nose going the same speed)

I would think that something that has a DV in the 100-125 range that he states would also have a similar penetration depth as a different bullet in the same DV range. I could be completely wrong here.

So what Veral states in that chapter is that as meplat diameter goes up for a given bullet weight and velocity, DV also goes up, but penetration goes down. Makes perfect sense because if more tissue is being displaced by a projectile of the same mass and starting velocity, that projectile will slow down and stop in a shorter distance due to the increased resistance of the increased volume of tissue it is displacing. But if you think two very different projectile with the same DV should penetrate to similar depths, do some calculations and see what you get.

Regarding some of these formulas, I would not go so far as to say they are "correct". This if for reasons such as using meplat diameter as apposed to meplat surface area (which is obviously more applicable). So my assumption is that the constants used are broad approximations that give calculated results somewhat close to real world results. Consequently, even if they prove fairly reliable across a broad range of loads, at the extreme ends of the range they are likely to produce numbers that won't quite line up with real world testing as well as the middle of the range.

But as we all know that a projectile is slowing down from the instant it leaves the barrel, and much more once it enters a medium denser than air, know we can't expect linear results throughout the entire bullet track. My conclusion is that the formulas are a coarse approximation, but somewhat useful none the less.

So I wouldn't worry too much about the constant values versus meplat or bullet diameters. They're just what makes the formula work. However, if you use the PWC formula to run th data in the chart from post #20, you'll find they come out pretty close. And I believe that data is from Veral's real world results. Though obviously, the velocities listed are rounded figures, and the wound diameter are probably not easy to measure with great precision.

 

[PLThomas]

So what Veral states in that chapter is that as meplat diameter goes up for a given bullet weight and velocity, DV also goes up, but penetration goes down. Makes perfect sense because if more tissue is being displaced by a projectile of the same mass and starting velocity, that projectile will slow down and stop in a shorter distance due to the increased resistance of the increased volume of tissue it is displacing. But if you think two very different projectile with the same DV should penetrate to similar depths, do some calculations and see what you get.

Regarding some of these formulas, I would not go so far as to say they are "correct". This if for reasons such as using meplat diameter as apposed to meplat surface area (which is obviously more applicable). So my assumption is that the constants used are broad approximations that give calculated results somewhat close to real world results. Consequently, even if they prove fairly reliable across a broad range of loads, at the extreme ends of the range they are likely to produce numbers that won't quite line up with real world testing as well as the middle of the range.

But as we all know that a projectile is slowing down from the instant it leaves the barrel, and much more once it enters a medium denser than air, know we can't expect linear results throughout the entire bullet track. My conclusion is that the formulas are a coarse approximation, but somewhat useful none the less.

So I wouldn't worry too much about the constant values versus meplat or bullet diameters. They're just what makes the formula work. However, if you use the PWC formula to run th data in the chart from post #20, you'll find they come out pretty close. And I believe that data is from Veral's real world results. Though obviously, the velocities listed are rounded figures, and the wound diameter are probably not easy to measure with great precision.

Ah! That makes sense, thank you

 

[JohnKSa]

The testing I want to do is to determine what role velocity plays in penetration with a bullet that does not deform.

There is a linear relationship, assuming the target medium is homogenous and the comparison is between bullets of similar frontal area that do not tumble.