Bullet Sectional Density (SD) ... the most meaningless variable for the hunter!!

[mcb]

It sort of funny. With internal ballistics you really want lower sectional density as this will tend to let you run faster burning powders making more efficient use of case volume resulting in higher muzzle velocities. As soon as we transition to external ballistics we want very high section density as high sectional density usually also means a reasonable high ballistics coefficients resulting in a flatter trajectory. As soon as we enter terminal ballistics on critters we want that sectional density to again be as low as possible without compromising bullet structure to make a larger wound channel.

As hunters we are pretty good at using bullets that go from high section density for the external ballistic phase and then transforming to low section density projectiles for the terminal phase. There has been some work going the other way mostly in military application but I have seen a few for civilian use also. Guns that are squeeze bore guns that start out with a low sectional density projectile and then squeeze the projectile up to a higher section density at some point down the barrel. Not sure I have ever seen it all brought together though since most military application want high section density in the terminal phase also as that is typically better at defeating armor.

rambling...

 

[Dibbs]

Well you're not alone in your thinking:
https://gundigest.com/gear-ammo/amm...od-measure-of-a-bullets-penetration-potential

From a hunting standpoint, SD has real meaning for me. 30 caliber works far better on medium and large game. 180 grain works far better than
150 grain, so, IMHO, makes for a faster cleaner, more ethical kill. This is a case where size actually does matter.

 

[earlthegoat2]

Just anecdotes but I have one shot killed and bang flopped more deer and hog critters with the most pathetic sectional density projectile in common use. The 12 ga foster slug.

I have never recovered one from any animal I have shot, though I have been party to folks who have shot them with a slug and there was no exit wound.

IMO, this is an example of sectional density being a load of bunk. For sure, the ranges were relatively short compared to typical rifle rounds but I only know what I’ve seen and I can tell you, what I have seen does not always agree with what I have heard or read.

I used to be a sectional density prophet too. In my younger days I read all the Chuck Hawks articles. He is a big proponent of sectional density and that is where I first heard the term.

I’m not going to say SD doesn’t matter. To me it does matter in the more roundabout way of me preferring heavy for caliber bullets. IMO, heavy for caliber bullets just kill game better.....which is to say faster. For me quicker kills=better kills.

I think momentum plays a part in all of this somewhere too. Large diameter and as such heavier bullets, even at relatively low velocities, still have enhanced killing power over their smaller brethren.

In terms of wounding, there are a few things to consider. Many folks are right that shot placement is paramount to harvesting game. If you hit an animal in the vital organs they are going to die. Where and when are the only questions after that. When game recovery matters hitting an animal in the boiler room is most important.

However, if you miss the vitals, will that animal still die? Maybe or maybe not. If it has a big hole in it then it will have a larger area to bleed from as well as a higher likelihood of infection down the line. The same likelihood doesn’t hold true for smaller holes.

How does this all relate to SD? Well I don’t know. What I do know is that at least in my own head is that if you don’t believe in sectional density then you probably do believe in big guns.

Let’s face it, 308 is a lot of gun for whitetail but a lot of folks still use it for that purpose and only that purpose. Once again, IMO, SD only starts to matter when you start using cartridges and bullet diameters that are marginal for the game being pursued. Then statements like “modern bullet technology” and “energy ft-lbs” start getting thrown around. All modern bullet technology does for me is make my adequate gun even more adequate. This is wher SD starts playing second fiddle to bullet construction.

 

[CraigC]

Not much to be honest. I run the gamut from light to heavy and don’t spend much intellectual energy on comparing theoretical lethality

Where I go overboard is in chasing accuracy. I spend a lot more effort developing loads than is necessary for a hunting round, and I do it primarily because I enjoy it.

Over the last 5 hunting seasons I’ve killed 7 deer.

4 were with .308s (2 - 150g, 1 - 165g, 1 - 180g)
2 were with a .358 (1 - 180g, 1 - 225g)
1 was with a .30-06 (180g)

All were one shot kills, all shots were between 100-150 yards, and none of the deer went more than 50 yards.

5 of those bullets listed above have different SDs. They all performed successfully with comparable results . A careful study of the abstract lethality based on SDs would have been an academic exercise with little value to me

Would you say, hunt elk with a 125gr .308 load? Or would you prefer something heavier? If so, for what reason(s)?

 

[LoonWulf]

Would you say, hunt elk with a 125gr .308 load? Or would you prefer something heavier? If so, for what reason(s)?

I'd honestly be curious to see what a 125gr monometal at 3300+ would do for elk. It's exactly opposite of the what I use, and I've always kinda wondered if it's a workable solution on larger stuff. I thought about trying it last cow hunt, but used my 6.5-284 with 143 eld-xs.

 

[Buckeye63]

I have always considered a bullets SD ... but frontal area is another factor, when looking at hunting bullets ....
The 6.5 X 55 with there Long high sectional density 160gr RN bullets is what they built there reputation on .. moderate speed , expansion & deep penetration ... momentum

The 30-06 , with the 200-220 gr bullet moderate velocity, deep penetration... momentum

The 45/70 400-450 gr bullet .. moderate velocity, large frontal area deep penetration... momentum

edit ;;; I forgot the 7mm Mauser ..175gr RN !!!

 

[Slamfire]

I have always considered a bullets SD ... but frontal area is another factor, when looking at hunting bullets ....
The 6.5 X 55 with there Long high sectional density 160gr RN bullets is what they built there reputation on .. moderate speed , expansion & deep penetration ... momentum

The 30-06 , with the 200-220 gr bullet moderate velocity, deep penetration... momentum

The 45/70 400-450 gr bullet .. moderate velocity, large frontal area deep penetration... momentum

The 30-40 Krag was considered a reliable killer with its 220 grain RN bullets going 2250 fps. I like these wound videos, the guy downloads the loads so the velocity is what you would expect at distance and measures the volume of damage. Those heavy lead projectiles from black powder weapons created massive damage on what they hit.

Lorenz bullet vs .58 Minié test in ballistic gelatine




Round ball vs cut lead - gelatine tests, accuracy, ballistics, historical background




Ballistic gelatine tests of the M 1867/77 Werndl rifle

https://www.youtube.com/watch?v=-_8eV8RvqBY



Shooting the Swiss Model 1851 Feldstutzer rifle


https://www.youtube.com/watch?v=xMBfUxmXK1c&list=PLIGg3pcPWcaJltGCC98OKAWsvPVALUp8Z

Remington 45-70 tests in ballistic gelatine



45/70 Sharps gelatine tests




Ballistic gelatine test of muzzleloading lead bullets vs modern 8x57 JRS hunting ammo.

 

[Garandimal]

@Slamfire, that is an excellent post ... as usual.



Compare these two bullets:

Hornady .264 cal 143gr ELD-X with a published SD of .293
Barnes .284 cal 170gr LRX with a published SD of .298

The SD values are virtually the same so which bullet would you expect to perform better on deer and elk? Assume similar MVs.

This is disingenuous.

Compare SD Between bullets of similar construction:
- Against bullets of different SD's w/in the same caliber.
- Against bullets of different calibers w/in the same SD.
- Against bullets of same Wt's but different caliber.

Eg.
A .270/150 gr. Core-Lokt will Penetrate better than a .270/130 gr. Core-Lokt. (Higher SD)
A .270/150 gr. Core-Lokt will Penetrate like a .30-06/180 gr. Core-Lokt. (Similar SD)
A .270/150 gr. Core-Lokt will Penetrate better than a .30-06/150 gr. Core-Lokt. (Higher SD)




GR

 

[MCMXI]

This is disingenuous.

Really? These are the questions presented by @CraigC.

Does bullet weight matter at all? Do you believe that in general, heavier bullets penetrate more deeply than lighter ones? If you answer yes to either of those questions, SD matters.

In my comparison, SD is irrelevant to the performance difference one would expect between these two bullets with essentially the same SD value. In response to my comparison @CraigC states ....

It's going to boil down to construction.

So remind me again of the significance of SD. To disprove a theory you only need to provide one example that illustrates that the theory doesn't apply to all cases and it falls apart. Read through the anecdotal posts in this thread where a bullet with higher SD exhibited less penetration than one with a lower SD. It's a straw man to state that SD matters because a 750gr .50 cal bullet will penetrate deeper than a 40g .22 cal bullet. That's what some are shoveling here. SD is is a derived value and not an intrinsic one. Mass is an intrinsic property.

 

[WestKentucky]

.358 diameter at 1500 FPS and 125 gr of mass killed just as dead as .277 diameter at 3000+ FPS with 130 gr of mass... but that’s nothing any more impressive than what the fraternities at college did with a .224 diameter bullet at 3000+FPS and 62 gr bullet or a .452 diameter bullet at 800 FPS with 230 gr mass. So what’s the big deal here? You don’t kill it if you don’t hit it, and it’s hard to whack a buck at 300 yards with a .45acp. They are all a means to an end, but some just work better than others. Ever wonder why so many things from so many makers end up looking the same? From 50 ft can you tell the difference between any of the bolt rifles on the market, or the brand of AR? When something works people copy it as closely as they legally can, sometimes closer. So, what has proven itself in design has become pretty well standardized into a few categories... 3000fps rifle bullets which are all fairly close in the various metrics, heavy stuff that’s slow and fat, or huge mouthed hollow points on stuff that’s kinda slow but only kinda fat. Notice there’s not many folks barking about using ELD bullets anymore? It didn’t fit the mold of the stuff that works well in the real world.

 

[Robert]

Some of y'all need to go to the range, if for nothing more than to get away from the keyboard and go outside. We are picking flyp out of pepper here...