Sectional Density and On-Game Performance?

[Jordan Smith]

A bullet can expand properly,and penetrate as well.Bullets that retain 100% of their weight will normally penetrate more than a bullet that expands to the same frontal area ,yet loses 40% or more of it's weight.That is why a bullet like the Barnes TSX or TTSX can do both very well.



I find that the Barnes MRX with it's tungsten core,provides the best combination in jacketed bullets.Of course,bullets like the TSX,and TTSX are not jacketed bullets,so your statement obviously doesn't apply to them.

+1

The TSX/TTSX also tend to penetrate deeper than bullets like the NF, SSII, Fusion, etc, because they have slightly less frontal area colliding with flesh and bone, due to the "X" design of the petals, rather than a big, round mushroom shaped frontal area. That doesn't necessarily mean that the X bullets do less damage, though, since they expand plenty wide, and make a fairly large wound channel.

 

[stubblejumper]

The TSX/TTSX also tend to penetrate deeper than bullets like the NF, SSII, Fusion, etc, because they have slightly less frontal area colliding with flesh and bone, due to the "X" design of the petals, rather than a big, round mushroom shaped frontal area.

The .308" TSX below expanded to a maximum width of .800",and has more than enough frontal area to provide a clean kill.You also need to remember that the bullet is spinning as it penetrates,so the x shape is cutting as it penetrates.

 

[Jordan Smith]

Yup, I'm right there with you on this, Stubble, believe me. We're batting for the same team on this issue, but the truth is that there is a little less resistance with the TSX-style bullets due to the little V-notches between the petals. Less resistance means more penetration. As I said before, however, they definitely expand plenty wide, and kill plenty well.

 

[hansol]

You want to have some fun with "Sectional Density"?

All it is is a ratio of bullet weight to length. All things being equal, a heavier bullet will have a greater SD ratio than a lighter weight bullet. Make a 250gr bullet in .308 cal for an uber SD bullet. Run the numbers if you don't believe me.

That's it. That's all.

 

[diemaco]

You want to have some fun with "Sectional Density"?

All it is is a ratio of bullet weight to length. All things being equal, a heavier bullet will have a greater SD ratio than a lighter weight bullet. Make a 250gr bullet in .308 cal for an uber SD bullet. Run the numbers if you don't believe me.

That's it. That's all.

Shouldn't that read diameter? I'm with you though that SD is esentially a ratio of weight and diameter and doesn't mean all that much. Unless you're talking about non expanding solids, SD has little to do with anything.

 

[Jordan Smith]

Bingo.

 

[ben hunchak]

For those drinking the TTSX Koolaid, check out the slug recovered on the big buck post, looks like an overpriced bullet to me, nice big buck and a congrats to the shooter/poster, but by the look of that recovered slug, he's lucky the deer isn't still running. When I recover a slug like that from test media I save it as an example of what I don't want a bullet to do on game!!!!

 

[hansol]

Shouldn't that read diameter? I'm with you though that SD is esentially a ratio of weight and diameter and doesn't mean all that much. Unless you're talking about non expanding solids, SD has little to do with anything.

ooooh I got a little ahead of myself. (heavier = longer, given a specific diameter) Thank you for the correction.

 

[stubblejumper]

For those drinking the TTSX Koolaid, check out the slug recovered on the big buck post, looks like an overpriced bullet to me, nice big buck and a congrats to the shooter/poster, but by the look of that recovered slug, he's lucky the deer isn't still running. When I recover a slug like that from test media I save it as an example of what I don't want a bullet to do on game!!!!

The picture of the TSX that I posted,was recovered from an elk,not from test media.

 

[Tumbleweed]

Semi-rookie hunter here. I shot two deer last year in my first season and one so far this year, so I have a bit of experience with shooting game, but nothing like what our more experienced forum members have accumulated.

My question is about bullet sectional density and what role it plays in on-game effectiveness of a cartridge/bullet combo. I know what sectional density is defined as, so I don't need that explained. Just how it affects the performance of a calibre and why some calibres (6.5x55, for instance) have reputations for being far more effective on game than their basic performance numbers would indicate.

Thanks,
Mark

I'll bet by now you're sorry you asked!

 

[Jordan Smith]

For those drinking the TTSX Koolaid, check out the slug recovered on the big buck post, looks like an overpriced bullet to me, nice big buck and a congrats to the shooter/poster, but by the look of that recovered slug, he's lucky the deer isn't still running. When I recover a slug like that from test media I save it as an example of what I don't want a bullet to do on game!!!!

Are you referring to the GS Custom HV???

 

[mmattockx]

I'll bet by now you're sorry you asked!

Getting there. Ben must have needed something to argue about, anyways.

Calling SD just weight is an oversimplification. I think the OP was asking about the performance on game of long narrow bullets(heavy for calibre). Traditionally 6.5x55mm(160 grain),7x57mm(175 grain),.303 British(215 grain) which all perform exceptionally well in large game e.g., they wade a lot of meat and tend to cut straight wound channels at moderate velocity.

I think this is a better way to phrase my question. I was wondering if the high sectional density was a significant portion of why the above mentioned calibres perform so well on game compared to what their rather pedestrian performance numbers would indicate.

As for the TTSX (and similar) bullets, if someone would make a 135-140gr .264" monometal bullet that shoots well out of my rifles I would never carry another calibre besides 6.5x55 for anything up to grizzly. Despite the testimonials and results of the big 6.5mm bullet test, the 120gr TTSX is just a bit light for my tastes and gives up too much BC (because of the low sectional density) to be my one go to bullet for most game.

Mark

 

[Republic of Alberta]

SD is just a commonly used yard stick that many shooters will recognize. It only has relevance in talking about two bullets from the same manufacturer, of the same design, that do not have some sort of expansion stops built in to them.



An example were SD is irrelevant would be compring say a 7mm Nosler partition vrs a the same SD 338 Nosler Partition. The partition in the 7mm is farther back than the 338's. So even though they have equal SD they will not have equal penetration at the same velocity.




If you want to understand more the first place to start would be learning about how velocity effects penetration on regular "cup and core" bullets. Move out in various directions from there. Always keep in mind there is no magic bullet. Penetration will always come at the price of wound diameter and vice versa, no one bullet will be the "best" at everything.

 

[BigUglyMan]

If you're shooting deer you're engaging in a completely academic discussion with little merit. But if you're shooting big, stoutly built creatures then SD can be important. Guys in the know recommend a bullet with an SD over .300 as a minimum for animals like buffalo, hippo and elephant. Animals requiring 10" of penetration are a whole different proposition than animals that can require up to 4 feet of penetration. Of course this is entirely based on using bullets that are adequately constructed for the task at hand, but SD is simply the relationship between the weight of the bullet and the frontal area. As the weight increases the SD increases. It is a real relationship that is not effected by pressure, temperature, humidity and all the other things that render BC a largely abstract term.

 

[BigUglyMan]

Shouldn't that read diameter? I'm with you though that SD is esentially a ratio of weight and diameter and doesn't mean all that much. Unless you're talking about non expanding solids, SD has little to do with anything.

Cross-sectional area, but you're pretty much right. Easier to use diameter than to calculate the area.

ooooh I got a little ahead of myself. (heavier = longer, given a specific diameter) Thank you for the correction.

Heavier = longer given a specific caliber and material. 180 MRX and TTSX will have the same SD but different lengths. Copper is lighter than Tungsten which is lighter than Lead which is lighter than Bismuth.

 

[Boomer]

Penetration in a fluid medium like tissue is a function of momentum. Momentum can be defined as that force which overcomes resistance against an object in motion. Thus if we have two non-expanding bullets of equal frontal area, shape, mass, and velocity, penetration of a given medium will be equal, but if one element is changed, there will be a difference in penetration. If we compare two expanding bullets, the amount of penetration is also effected by the final frontal area of the expanded bullets, and by their retained weight.

Shooting live targets never reproduces exact bullet performance, but it does produce a trend which can be used for comparative purposes. Seldom are two animals exactly the same size, density, target angle, or range, and it is seldom that the bullet tract on two different animals would be exactly the same. No animal is a homogenous mass, and all animals are made up of skin and hide of various toughness, bones of various density and hardness, tissue of various density and thickness, and of hollow areas which hold nothing but air. All of these elements enter into the penetration formula. But when we shoot with suitably designed bullets, we know that penetration will be sufficient to get the job done in that the additional velocity of lighter bullets relative to a heavier bullet or the additional mass of the heavier bullet relative to a lighter bullet, results in exactly the same penetration of that specific target.

 

[Danny Boy]

I accept SD is a good guideline to measure bullet penetration.

I was trained in the old school; always use the heavier bullets that your rifle can shoot accurately. Generally that translates to higher sectional density. The bullet I have used for many years was the Nosler Partition which held up well for a deep penetration.

In 2005, I became aware of the effects of lead bullet fragments and started transitioning to the TSX. As many have experienced, you don’t need the same heavy weight bullets in TSX as you would in other premium bullets like Partition for penetration. I optimized the overall performance by stepping down on selected bullet weights in favour of higher speed. TSX brings in good if not better results.

The transition to TSX in load development was not cheap for the rifles and calibers that I own. It is not something that I have time and spare change to do every year when manufacturers come up with new bullets. The bottom line is that I am happy with the TSX for big game hunting.