Sectional Density - Desert Dog

[Beck]

I generally find this guy to be entertaining, and somewhat knowledgeable. I have found myself disagreeing with him on a handful of occasions, and this is certainly one of them. I am a believer in sectional density, but I guess he thinks it's bullshit. What do you think? Video below:

 

[CBeck]

Sectional density matters to penetration because it describes how much mass is concentrated behind a given frontal area of a bullet.

• Higher SD = more weight behind a smaller cross-section

When a bullet enters any medium, it slows down because of drag. A bullet with higher SD:

1. Has more momentum per unit of frontal area
2. Loses velocity more slowly
3. Pushes deeper before stopping

But, I agree SD isn’t all that matters…..

Penetration is influenced by several factors working together:

1) Bullet construction (huge factor)

• Bonded / solid / monolithic bullets retain weight → deeper penetration
• Fragmenting or soft bullets lose mass → less penetration

2) Expansion

• When a bullet expands, its effective diameter increases, which reduces penetration (even if original SD was high)

3) Velocity

• Higher velocity increases penetration until expansion or fragmentation increases drag

 

[Beck]

Sectional density matters to penetration because it describes how much mass is concentrated behind a given frontal area of a bullet.

• Higher SD = more weight behind a smaller cross-section

When a bullet enters any medium, it slows down because of drag. A bullet with higher SD:

1. Has more momentum per unit of frontal area
2. Loses velocity more slowly
3. Pushes deeper before stopping

But, I agree SD isn’t all that matters…..

Penetration is influenced by several factors working together:

1) Bullet construction (huge factor)

• Bonded / solid / monolithic bullets retain weight → deeper penetration
• Fragmenting or soft bullets lose mass → less penetration

2) Expansion

• When a bullet expands, its effective diameter increases, which reduces penetration (even if original SD was high)

3) Velocity

• Higher velocity increases penetration until expansion or fragmentation increases drag

I agree with your assessment. His video amuses me a bit because he emphasizes mass and momentum, both of which are fundamental components of sectional density.

 

[Hunter-Habib]

I am a big believer in heavy-for-caliber bullets. As long as velocity is still adequate.
Such as:
173Gr for 7x57mm Mauser
220Gr for .30-06 Springfield, .300 Holland & Holland Magnum, .300 Winchester Magnum
250Gr for .338 Winchester Magnum
286Gr for 9.3x62mm Mauser
400Gr for .404 Jeffery
550Gr for .450 Rigby Magnum
600Gr for .505 Gibbs

Sectional density makes a difference in penetration but only if all other factors are equal.

For certain game animals, a slightly lighter bullet in certain calibers aids in getting velocity up. Take lion hunting or leopard hunting with a 9.3x62mm Mauser, for example (also tiger hunting, back when hunting them was legal). If I were using this caliber to hunt an elephant, I would prefer a 300Gr solid. But for hunting the great cats, I would prefer a 286Gr soft point so that case capacity (and thereby velocity) could be increased. The great cats possess a highly developed central nervous system and are quite susceptible to the shock generated by high velocity bullets (even if said bullets are a little light).

 

[Beck]

I am a big believer in heavy-for-caliber bullets. As long as velocity is still adequate.
Such as:
173Gr for 7x57mm Mauser
220Gr for .30-06 Springfield, .300 Holland & Holland Magnum, .300 Winchester Magnum
250Gr for .338 Winchester Magnum
286Gr for 9.3x62mm Mauser
400Gr for .404 Jeffery
550Gr for .450 Rigby Magnum
600Gr for .505 Gibbs

Sectional density makes a difference in penetration but only if all other factors are equal.

For certain game animals, a slightly lighter bullet in certain calibers aids in getting velocity up. Take lion hunting or leopard hunting with a 9.3x62mm Mauser, for example (also tiger hunting, back when hunting them was legal). If I were using this caliber to hunt an elephant, I would prefer a 300Gr solid. But for hunting the great cats, I would prefer a 286Gr soft point so that case capacity (and thereby velocity) could be increased. The great cats possess a highly developed central nervous system and are quite susceptible to the shock generated by high velocity bullets (even if said bullets are a little light).

Exactly. Factors I consider when choosing a bullet include Mass, Velocity, Shape, Construction (to me includes material), Sectional density, game being hunted, and caliber.

 

[CBeck]

I get what he’s saying ….sectional density does not matter as much when comparing, for example, a monolithic bullet to a soft expanding bullet… I could agree with that…. but wait, I actually don’t agree that, it does matter.

A lower‑sectional‑density monolithic bullet can penetrate deeper than a similar sectional‑density soft bullet because penetration is driven more by retained weight and expanded diameter than by original sectional density.… but I can look for a higher sectional density soft to equal the penetration of a lower density monolithic bullet…..so in this example I AM still using sectional density as a predictor of penetration.

 

[Aaron N]

The guy annoyed me in the first 30s, did he do tests with ballistic gel to prove his point? Or was it essentially click bait?

 

[Tanks]

SD does not seem to matter with mono bullets with the right bullet design. @michael458 did exhaustive tests on it.

 

[CBeck]

The guy annoyed me in the first 30s, did he do tests with ballistic gel to prove his point? Or was it essentially click bait?

Agree… he acted like he was nervous… Lol

 

[schwerpunkt88]

I'm waiting for Desert Dog to weigh in on this one..."somewhat knowledgeable," that's pretty rich. I can't think of any other YouTuber who has a broader AND deeper understanding of all things hunting, fishing, and guns who has more integrity in his videos than the Desert Dog. He and I have even disagreed on a non-related subject, but you have to respect his knowledge.

 

[CBeck]

SD does not seem to matter with mono bullets with the right bullet design. @michael458 did exhaustive tests on it.

Within the same bullet design and construction, sectional density absolutely matters.

Let’s compare .375 caliber monolithic bullets same brand and model:

A 270‑grain mono will generally penetrate deeper than a 250‑grain mono.

In my thought process, why Sectional Density Matters…..

With monolithic bullets

• Weight retention is nearly 100%
• Expansion is controlled and very consistent
• Construction is identical

Because those variables are essentially held constant, the remaining differences are:

1. Sectional density
   • 270 gr (.375) SD ≈ 0.274
   • 250 gr (.375) SD ≈ 0.254
2. Momentum
   • The heavier bullet carries more momentum at similar velocities
3. Resistance vs mass
   • Same expanded diameter
   • More mass behind that frontal area

Result: Higher SD + more momentum = greater penetration

 

[Beck]

I'm waiting for Desert Dog to weigh in on this one..."somewhat knowledgeable," that's pretty rich. I can't think of any other YouTuber who has a broader AND deeper understanding of all things hunting, fishing, and guns who has more integrity in his videos than the Desert Dog. He and I have even disagreed on a non-related subject, but you have to respect his knowledge.

Yea, I am going to side with Kevin Robertson on this one. I don't think sectional density is a "lie". I might agree if he'd said "sectional density is less important than bullet construction", but he didn't say that did he?

 

[sgt_zim]

The math gets kinda weird with softs. Slower impact velocity means less expansion, so SD stays nearer to an unfired state than when impact velocity is higher and expansion is greater.

And then there is Randy Garrett's test with caliber 458 solids on saturated newspaper, where 45-70 out-penetrated 458 WM, which out-penetrated 458 Lott, which out-penetrated 460 Wby mag.

PENETRATION: THE 45-70 & 458 MAGNUMS

There is something about a projectile's interaction with water that we don't really understand, and since flesh is 70%+ water, seems like something we should try and understand better. How we might come to a better understanding of it is a hard thing in a dynamic and dangerous situation like testing bullet penetration, and we can only come up with rough proxies and our anecdotal experiences.

And that's all complicated by the fact that flesh is an inconsistent medium - we have to include bone, and different layers/density of muscle, plus connective tissue.

Sorta like the dictum from the novel "Dune," only the slow blade penetrates (the shield).

All that aside, I generally shoot the heaviest weight (and slowest) bullets (and therefore the highest SD) available for a given cartridge.

When I go back to Africa next year, I'll bring 430 gr for my 404 and 350 gr for my wife's 375; though I'll probably just stick with 286 gr if I decide to bring my 9.3x62.

 

[375Fox]

I don’t think sectional density is BS, but I do think it’s outdated. Maybe it’s a good predictor of penetration with the same bullet, but bullet design and construction are a lot more important.

 

[375Fox]

I might agree if he'd said "sectional density is less important than bullet construction", but he didn't say that did he?

Maybe not that exact wording but that’s what I heard.

 

[schwerpunkt88]

Yea, I am going to side with Kevin Robertson on this one. I don't think sectional density is a "lie". I might agree if he'd said "sectional density is less important than bullet construction", but he didn't say that did he?

I'm not arguing about sectional density...I responded to the backhanded insult of Desert Dog

 

[Beck]

I'm not arguing about sectional density...I responded to the backhanded insult of Desert Dog

You must be pretty delicate if you think that is a "backhanded insult"

 

[dchum]

Yes, comparing projectiles of all different types, construction and design is completely pointless and an antiquated method that is useless and is just numbers on paper.

Tough pill for many to swallow.
Tissue damage kills not SD or anything else.

 

[Beck]

Yes, comparing projectiles of all different types, construction and design is completely pointless and an antiquated method that is useless and is just numbers on paper.

Tough pill for many to swallow.
Tissue damage kills not SD or anything else.

It is an attribute, not the bible

 

[sgt_zim]

Yes, comparing projectiles of all different types, construction and design is completely pointless and an antiquated method that is useless and is just numbers on paper.

Tough pill for many to swallow.
Tissue damage kills not SD or anything else.

Tissue damage is a result of expansion and penetration.

Obviously solids penetrate the deepest, but at the expense of no expansion. Unbonded softs expand the most, but at the expense of penetration.

SD only informs on the potential for penetration. Higher SD speaks to a greater potential for penetration than lower.

I'm pretty sure you could get this fellow up to 2700 or 2800 out of a 458 Lott

But I'm also pretty sure nobody's hunting cape buffalo with it, either.