What is this Sectional Density? How do I use the numbers to help my shooting?
THANKS
Jerry

JY, sectional density is a ratio of a bullets weight to its diameter. SD affects the teminal performance of a bullet. It won't really help your shooting. The higher the SD, the more penetration you can expect from a given bullet. So if you are shooting large, heavy game like elk, moose, or bears, you will want a bullet with a fairly high SD(most will say around .270). However, if the game is strictly whitetails, SD really does not matter IMHO as they are fairly easy to kill.

quote:

Originally posted by jy:
What is this Sectional Density? How do I use the numbers to help my shooting?
THANKS
Jerry

SD is the mathmatical relationship between the diameter and weight of a bullet.

I am biased in my opinion but I do have some thoughts about Sd.

The ancients (people who hunted before Mr. Weatherby) noticed that they had better results on game with heavier bullets, when choosing between different weight bullets in the same caliber. I don't think they invented their results, they just observed results. This seemed to be most prevalent with thick skinned big game. That's all sectional density is. It doesn't mean you can't kill an animal with a lighter bullet, people do it all the time. Nor does it mean that high SD bullets always work, there are just too many variables to make equations the only explanation for what happens in hunting.

quote:

I don't think they invented their results, they just observed results. This seemed to be most prevalent with thick skinned big game.

This has been debated at length before.

SD becomes more important as we move up to the big stuff, but it cannot stand on its own. We need to get the bullet into motion. The velocity also cannot stand on its own. Putting more weight behind a given area will improve penetration as momemtum levels can be escalated this way easier than by velocity increases. Momentum on its own cannot stand in isolation. We need to consider the size of the hole that will provide the drag. So the simplest single measure is to relate the bullets's momentum (Mass x Velocity)to its frontal area. That is why a 375 H&H can out penetrate a 458 Win at standard factory velocities.

The 500 gr .458 bullet has a higher SD value (.341) and a higher momentum value than the 300 gr .375 bullet with an SD of .305. Only when we relate the momentum to the frontal area, do we get the explanation as to why the one out penetrates the other, suppose we use solids to avoid other complexities.

SD comparisons must be confined to the same caliber.

Warrior

What Warrior said.

Also, sectional density comparisons should be confined to comparable bullet constructions. That is to say it's not useful to compare the sectional density of a cup and core bullet to a monometal bullet (Barnes TSX) or even a bullet with a lead front and monometal shank (TBBC or Northfork). The latter are much longer than a traditional cup and core bullet.

IMO, the sectional density is not as useful today as it once was with the premium bullets available. I.e. a premium bullet may perform better than a very high sectional density lead core bullet.

LWD

quote:

Originally posted by jy:
What is this Sectional Density? How do I use the numbers to help my shooting?
THANKS
Jerry

It's an absolute meaningless number that sounds real mysterious when it comes to shooting most any game animal, but, you'll be fine, so long as you use common sense and the right tool for the game at hand.

From an internal ballistics point of view, SD relates how easy it is to accelerate the bullet. A lower SD bullet is easier to accelerate with combustion gas at a given pressure. This is one factor used to help identify a powder burn rate that is appropriate.

" It's an absolute meaningless number that sounds real mysterious when it comes to shooting most any game animal"

Really when in fact this "insignificant number" underlies and is fundamental to the very proccess of penetration of a projectile in a target. The ability of a projectile to breech a target is absolutely dependent on this "insignificant number" and more precisely the "energy density" or energy transfer per reference area of a projectile that allows it to overcome the resistance afforded by the target to penetration.

The "number" however is not represented by the SD number refered to or printed in loading manuals.

As Gerard is so fond of pointing out the SD of a bullet sitting on the bench is of no significance

The "real" or "working" SD is represented by the ratio of a bullets weight to the reference area of the presenting part of the projectile in the direction of it's motion. The crux lying in the part referring to motion.

The practical implication of this fact underlies the importance of projectile stability in target for non deforming projectiles. A solid bullet may have exceptional SD whilst in stable motion, however in unstable motion the SD assumes a very low value and poor penetration

Confined to a specific caliber and the same bullet type (read construction), SD is significant. Couple of things work in its favour of the higher SD bullet (heavy) in comparison to the lower SD bullet (light), when we shoot expanding bullets in particular:

1) combination of higher momentum & lower energy
2) Drag less with lower velocity of heavier bullet
3) bullet opens slower and do not over-expand to same extent
4) bullet maintains more mass and does not shatter to same extent

All of the above contribute to deeper penetration, provided that the bullet is used within in its working window and adequate stability is assumed.

Warrior

There are several good points here. Wink mentions the observations of the Ancients. Their observations were entirely correct, of course. Heavier lead core bullets, in the same caliber, undoubtably penetrate deeper than similarly constructed bullets that are lighter, when both are fired at similar pressure levels. The Ancients attributed this to higher Sd, or did they?. Surely they knew that the real reason was fragmentation. The faster you run a lead core bullet, the more it breaks up and the shallower the penetration. I am sure the Ancients saw the logic of this and, by saying that higher Sd bullets are better, they were simply using a form of shorthand, knowing that logic will fill in the gaps. Fortunately, with the advent of CNC technology, the era of the Ancients has now passed and we need not fret about bullet disintegration any more.

Warrior says "SD comparisons must be confined to the same caliber." This is a pretty useless exercise as there is little point in comparing the Sd of two bullets sitting on their bases on the loading bench. (Thanks for remembering, Alf). Surely comparisons within a calibre would involve shooting the bullets compared. Describing a bullet in motion by claiming it has a sectional density of "x", has as much value as saying it is shiny, not dull. Imagine two guys discussing the penetration depth of two bullets fired into ballistic gelatin: "I do not know how to explain this. These two bullets were both polished to the same degree of shininess but one went way deeper than the other. They are the same caliber, the same construction and fired from the same rifle. Do you suppose that the 200fps difference in speed could be the cause?" His friend: "Dunno..... both were equally shiny..... beats me."

Doc is very clear in his assessment of Sd. Well said indeed and BigJakeJ1s makes a good point too. To his remark one must add that Sd also determines to what extent a bullet will self destruct when forced to decelerate by the object that is hit.

Alf, as usual puts his finger right on it in a roundabout sort of way. Torn between two points of view, it seems. On the one hand there is: "Sd underlies and is fundamental to the very proccess of penetration of a projectile in a target." On the other hand he says, and I paraphrased the comment for clarity: "The ability of a projectile to breech a target is absolutely dependent on the "energy density" or energy transfer per reference area of a projectile that allows it to overcome the resistance afforded by the target to penetration." He also confirms the correct line of thought with: "The real or working "SD" is represented by the ratio of a bullets weight to the reference area of the presenting part of the projectile in the direction of it's motion. The crux lying in the part referring to motion." (Alf, I moved your quotation marks around for clarity in the last sentence.) These are very good descriptions, confirming the worthlessness of Sd which is neither a force, power or form of energy and has no value in describing how much work can be done by any object in motion.

Warrior makes a number of points with which I do not agree but what is new about that? The point about more momentum and less energy is somewhat outdated. Within a caliber, lighter bullets can match the momentum values of heavier bullets, or come so close that the difference does not matter. In that case, the lighter bullet will have more energy and, given the choice between two bullets of similar momentum with one having more energy, the choice is a no brainer. Secondly, if a bullet produces lower drag, it also does less work on the target. This translates to narrower wound channels which may be a problem. Points 3 and 4 are incorrect and has been disproven by McPherson in "Bullet Penetration" and by practical observation. Do the manufacturers of heavy for caliber lead cored bullets themselves not correctly claim massive (Sd driven) expansion?

Lighten up guys, have some fun.

/

The difference between a golf ball and a ping pong ball is sectional density. Throw each one as far as you can to see the effect.

quote:

The difference between a golf ball and a ping pong ball is sectional density.

One hundred percent correct! Until you pick them up and throw them.

quote:

Throw each one as far as you can to see the effect.

My point exactly. If the golf ball and ping pong balls are the same diameter, the effect you observe when you throw them is: Increased momentum better overcomes the resistance produced by cross sectional area and the medium being penetrated. It is a slightly skewed example though, like comparing a mono solid to a jacketed hollow point target bullet.

Alf, you have just confirmed again that Sd is meaningless as a pointer to likely performance. Correctly, the momentum that is applied to the cross sectional area exposed to the direction of travel is the correct way of looking at it. Why do you guys insist on furthering the myth of Sd? Shed the shackles and call things by their correct names.
Sd = Correct as a descriptor for a bullet at rest.
Momentum = One form of describing the potential of a bullet in motion.
Energy = Another form of describing the potential of a bullet in motion.
Mass = A bullet at rest
Weight = Also a bullet at rest at a certain point on Earth somewhere
Speed = Useful for calculating some of the potentials above.

and so forth.

quote:

Originally posted by ALF:
" It's an absolute meaningless number that sounds real mysterious when it comes to shooting most any game animal"

Really when in fact this "insignificant number" underlies and is fundamental to the very proccess of penetration of a projectile in a target. The ability of a projectile to breech a target is absolutely dependent on this "insignificant number" and more precisely the "energy density" or energy transfer per reference area of a projectile that allows it to overcome the resistance afforded by the target to penetration.

The "number" however is not represented by the SD number refered to or printed in loading manuals.

As Gerard is so fond of pointing out the SD of a bullet sitting on the bench is of no significance

The "real" or "working" SD is represented by the ratio of a bullets weight to the reference area of the presenting part of the projectile in the direction of it's motion. The crux lying in the part referring to motion.

The practical implication of this fact underlies the importance of projectile stability in target for non deforming projectiles. A solid bullet may have exceptional SD whilst in stable motion, however in unstable motion the SD assumes a very low value and poor penetration

Right. Still meaningless. Whether talking about a printed SD number in a manual or if figuring it out, it doesn't amount to a hill of beans on some of the most popular game animals.

Reports of 6mm TSX bullets weighing 85 grains passing through bull elk are quite telling....printed SDs of low 0.2s.

Sierra 44 cal pistol bullets weighing 240 grains with printed SD of ~ .186 penetrating and exiting adult mule deer in the 285 pound range quartering away.

Hornady SST 30 cal, 180 with printed SD of .270+ blows up on hide of South Carolina whitetail buck at 190 yards.

Not to mention all of the match grade bullets that are used on game where some work and some don't but have "adequate" SDs to penetrate.

It's STILL a meaningless number in the real world of hunting game, so long as you use common sense and the right tools for the game at hand.

quote:

Originally posted by Gerard:
I am biased in my opinion but I do have some thoughts about Sd.

So sectional density has nothing to do with determining the trajectory of a bullet.

Oh really? Sectional density divided by the "form factor", (a numerical value for the shape of the bullet), DOES, because that number IS the ballistic coefficient of that bullet!

If two bullets of equal form but different sectional densities are launched at the same MV, the one with the higher sectional density will shoot flatter and lose less velocity over the same range. Yes, it has a higher B.C. because it has a higher S.D.

Likewise, if two bullets having identical structure and shape but different sectional densities are fired at the same MV, the one with the highest SD will out-penetrate the other in identical media (flesh, bone, air, etc.) This only changes if the S.D. changes during penetration, for example, by expanding and thereby reducing S.D. in the process.

Now, do we put too much emphasis on this difference? Perhaps so...... And, as pointed out above, you cannot use sectional ddensity to compare the likely performance of projectiles of different construction.

/

Yes, recently a penetration test involving .45 caliber rifles, found that in the .45/70, maximum penetration for a 420-grain hard cast bullet was produced at a MV of 1550 FPS. Any significant increase in MV resulted in a measurable degradation of penetration, even though none of the bullets expanded at ANY of the impact velocities........

/

Yea, and the most interesting part is what a waste of time it was.

I'm sure SD is important to someone, but your average Joe hunter has never heard of it and doesn't give a hoot. The ammo makers have done a fine job of letting the public know what bullets are made for what type of game.

Doc, I know what you said. Can you tell me what anybody else said? In layman's terms, I think this is called mental masterbation!

quote:

I'm sure SD is important to someone, but your average Joe hunter has never heard of it and doesn't give a hoot

Even if the average Joe owns a 30-06, and does not care for other calibers or any sort of ballistic events or tests, and let us assume Joe has forgotten all his school maths, but he possesses only field experience, he knows full well that he can buy 130 grain, 150 grain, 165 grain and 180 grain bullets for his rifle - that implies increased SD. SD is just the term to make these jumps, and Joe will select the one that he believes work best for him, thereby discriminating against the others. I am sure Joe, being the simpleton, will reason to pick the heavier bullet as his quarry gets bigger. Never mind ol' Joe is just an idiot.

If all the methematicians/ballisticians over the last 100 years wasted their time, as Doc says, then they must have been dumber than ol' Joe.

El Deguello,
Just as sectional Density is a simplistic way of looking at certain facts around external and terminal ballistics, using Sd to calculate BC is similarly simplistic and misleading. BC is best arrived at by using Cd instead of Sd. For example, Cd takes into acount the varying drag numbers that occur when speed goes up or down and more accurately allows for varying shapes.

The correct formula is therefore: BC = Mass /(Cd x cross sectional area)

When you say: "Yes, it has a higher B.C. because it has a higher S.D." I think it is better to say: "Yes, it has a higher B.C. because it has a lower Cd."

Similarly the statement: "the one with the highest SD will out-penetrate the other in identical media" is true but not correct. Yes, it has a higher SD but the reason why it penetrates better is because it has more momentum. Sd cannot make a bullet penetrate more or less but momentum can. No?

Alf,

quote:

we see that we cannot exchange velocity in lieu of weight in the penetration proccess.

This is true if we look at extreme situations created for experimental reasons. In reality velocity is a good substitute for weight when bullet design is done with the probable speed range and required penetration in mind.

130gr 7mm

quote:

the heavier projectile will need less velocity than the lighter bullet to breech the target

Of course it will. Depth of penetration is determined by the momentum applied to the cross section. So, for similar momentum levels and depth, the heavier bullet must be slower. The downside of using the heavier bullet is provided in your statement: "if it does not deform, become unstable or fragment". Heavy bullets are more prone to do this than lighter ones, not so?

For similarly constructed bullets, heavier bullets are more likely to shed weight when speed is the same as that of a lighter bullet, because bullet destruction in the target is both speed and Sd driven. When lighter bullets are typically driven faster than heavy ones, they again tend to shed more weight. So here is the solution to why monometal bullets can be applied over a wider window of application than jacketed lead bullets. They are impossible to blow up from a shoulder fired weapon. With that limitation removed, advantage can be taken of driving them fast and enjoying the benefits of much improved external ballistics.

You provide the bottom line yourself with: "It would also appear that there are limits to this proccess so that the proccess of penertation happens within a definite window of limitations with regards to mass velocity and reference area." The operative part being "mass velocity and reference area" and that is not Sd.

El Deguello,

quote:

Yes, recently a penetration test involving .45 caliber rifles, found that in the .45/70, maximum penetration for a 420-grain hard cast bullet was produced at a MV of 1550 FPS. Any significant increase in MV resulted in a measurable degradation of penetration, even though none of the bullets expanded at ANY of the impact velocities........

This is a perfect example of why Sd is worthless as a likely indicator of performance. A wide variety of penetration results were obtained with bullets that all have the same Sd.

Alf,
At least Karl and Beat use the correct formula for getting to Sd, but you take my statement of a "worthless number" out of context. I have always said that it is worthless as an indicator of probable terminal performance. Of course it is usefull for the calculations of complex formulae (if it is calculated correctly and not as some do when it implies square bullets) and when it is combined with motion and expansion and such. No problem with that at all. Just do not try to tell me that one bullet is superior to another purely because it has a higher Sd.

Warrior Chris,

quote:

he knows full well that he can buy 130 grain, 150 grain, 165 grain and 180 grain bullets for his rifle - that implies increased SD.

True, but Joe Hunter, being the simpleton he is, having never heard of Sd, is more likely thinking "heavier" rather than "This relationhip between projectile mass and it's reference area is a fundmental part of the whole penetration process" (as Alf said)

quote:

If all the methematicians/ballisticians over the last 100 years wasted their time, as Doc says, then they must have been dumber than ol' Joe.

I am going to ask for something here. All of you who are enamoured with this magical thing called Sd: Show me one reference where a ballistician/researcher/experimeter of good standing attributes increased terminal performance to Sectional Density. Not Sd plus projectile construction or Sd plus velocity or Sd plus form factor or Sd plus the phases of the moon, just Sectional Density.

PS. Chris, you can stop pretending that you are Warren. Just sign your real name, you are misleading the newcomers to the forum.

quote:

I'm sure SD is important to someone, but your average Joe hunter has never heard of it and doesn't give a hoot.

I agree! Your average Joe Hunter" doesn't even know how to zero his rifleand has the local gunsmith do it for him! But the guys who post here are NOT "your average Joe Hunter"......

quote:

Originally posted by El Deguello:

I agree! Your average Joe Hunter" doesn't even know how to zero his rifleand has the local gunsmith do it for him! But the guys who post here are NOT "your average Joe Hunter"......

That's not true. I know a lot of very good hunters who can shoot very well but they do not have the time to spend at the range that they'd like. And some do not even know how to turn on a computer. 3 come to mind that have been hunting and shooting for 40-50 years or more.

As for the local gunsmith doing it for them, I know a few gunsmiths. I worked with 7 in Tucson. I know Sizemore in north Alabama, who was a smith for the 1984 Olympic shooters. I know 5 here in Ohio and northern KY. Not one has the time nor inclination to sight someone elses rifle in.

We can dance around this SD topic for weeks if you wish, and you can slam hunters and shooters that have no desire to frequent any shooting websites and make them seem inferior to AR members, but there are plenty of very good guys out there who are ethical shooters and hunters that use good bullets in adequate calibers to pursue big game, and sectional density is nothing more than a number on a box and the bullets just keep piling up game for them year after year.

quote:

Originally posted by Warrior:
If all the methematicians/ballisticians over the last 100 years wasted their time, as Doc says, then they must have been dumber than ol' Joe.

Not dumber, just too bored.

All the arguments on the planet, don't take away from what I have personally experienced in my hunting career...

give me a high sectional density bullet any day, over a lower sectional density bullet.. especially if the size of the game increases...

Low sectional density bullets will penetrate deeper, if driven at lower speeds.. contrary to the popular hunting circle myths......

High sectional density bullets don't come apart like lower SD bullets at high velocity...

Anyone ever had a 220 grain RN in 30 caliber fail?? or a 160 grain Bullet in 270 cal fail?? or a 175 grain RN in 7 mm fail???

If you have, you are part of a small unique crowd...

quote:

Originally posted by Don Fischer:
Doc, I know what you said. Can you tell me what anybody else said? In layman's terms, I think this is called mental masterbation!

Yep. That's exactly what it was for all of those bored mathematicians!!

Seafire,
What you say holds true for jacketed lead bullets, no doubt. My issue with Sd is that the advent of monometal bullets has made it redundant. Specifically, in the samples you mention, on game a 160gr 30cal will consistently go deeper than a 200/220gr lead core bullet. It will also do this at greater range, with less wind drift and, at close range, with more reliability. This was confirmed by a test done by Magnum magazine a couple of years ago. Ditto for a 110/120gr 270 mono except the Magnum magazine test.

The 7mm sample is particularly close to home. I fired my first shot at a game animal in 1958 with a 7x57 with Kynoch 173/4gr soft points. In 1992 I came desperately close to losing a kudu after shooting it with a 173gr partition style bullet that failed. In between I have had the typical mixed bag of results that one has with lead core bullets. Since 1992 I have been using 140gr monos and from 1997 to 2002, 130gr monos. In that ten year span, involving more than a hundred animals, I have not had a single bad result with any of my 7x57s.

Bullet construction works. To me Sd is just a number that carries no weight.

Gerard, I have a question: if a monolithic solid, not designed to expand (Barnes Banded Solids?), and in the same caliber (say .416) one bullet weighs 350 grains and the other weighs 400 grains but are otherwise identical, and I am me and don't know which one to buy, but I do know I will be hunting buffalo at under one hundred yards, why would I pick one or the other?

OK, why shouldn't I jump in here too. ??

Sectional Density was a figure given to hunters in the early days of jacketed bullets to help explain why "heavy" bullets, in caliber, penetrated further. Bullets in those early days were basically indentical, varing only in weight and nose shape so SD had significance.

All that started changing in the 50s when custom bullet makers came on the scene. Yes, if today's bullets were still made "equal", the ones with a higher SD would still penetrate better. But, today, few things are equal. Penetration now depends more on bullet construction rather than mass alone, making arguments of the SD of a hunting bullet largely irrelivant.

An illustration of what I mean; A golf ball and a small egg are about the same size and weight so their SD is close as well. But toss both at the same speed and we all know one won't penetrate worth a damn!

So, forget SD except as a campfire topic, it just isn't relivant to hunters today. Especially for those of us who reload with a wide variety of bullet construction designs at hand.

quote:

Originally posted by Jim C. <><:
But, today, few things are equal. Penetration now depends more on bullet construction rather than mass alone, making arguments of the SD of a hunting bullet largely irrelivant.

That's exactly right. Case in point, 2 bear hunters, 2 30.06 rifles, two bears, both about 225 pounds, 2 bullets both through the shoulders.

Bullet 1, 180 Scirocco, SD ~ .271
Bullet 2, 220 Corelokt, SD ~ .300+

Scirocco passes through and leaves BIG hole in dirt after penetrating 2 shoulders. Corelokt recovered fully mushroomed on INSIDE of offside shoulder.

2 dead bears, no bullet failures, the lower SD bullet outpenetrated the higher one...why? Because of bullet construction.

SD, a real number, mathematically derived, but nothing more than a topic for debate...but it's been fun so far, might as well keep it going.

quote:

All the arguments on the planet, don't take away from what I have personally experienced in my hunting career...

I agree 100%.

quote:

Originally posted by Warrior:
Even if the average Joe owns a 30-06, and does not care for other calibers or any sort of ballistic events or tests, and let us assume Joe has forgotten all his school maths, but he possesses only field experience, he knows full well that he can buy 130 grain, 150 grain, 165 grain and 180 grain bullets for his rifle - that implies increased SD. SD is just the term to make these jumps, and Joe will select the one that he believes work best for him, thereby discriminating against the others. I am sure Joe, being the simpleton, will reason to pick the heavier bullet as his quarry gets bigger. Never mind ol' Joe is just an idiot.

I consider myself to be an average Joe. I'm not some elitist shooter/hunter, and maybe to you I am an idiot. However, bigger/heavier bullets aren't always best. In fact, it is laughable. I'd take a 110 TSX in a standard 270 rifle over a 135 grain Sierra MK, or 150 SST anyday for deer.

I think we can both agree that the heavier bullets have a higher SD.

But the CONSTRUCTION of the TSX is superior, even the 110, for hunting.

SD, a completely over-rated, over-discussed number....where in the real world of soft tissue trauma, it is STILL MEANINGLESS. And so far, no one has PROVED otherwise, with respect to HUNTING. In fact, I have seen for myself just the opposite and I've given some examples.

quote:

I'd take a 110 TSX in a standard 270 rifle over a 135 grain Sierra MK, or 150 SST anyday for deer.

Doc,

Deer is a soft thin-skinned specie and it can be killed with light bullets featuring low SD's. It is even done with .243/90 gr Nosler Partitions over here with body shots. With head shots it is done with the dinky .223/55 gr bullet.

You should not be comparing a strongly constructed mono-metal bullet like a TSX with a frangible thin-jacketed lead-core bullet like a Speer. That is why I stated clearly that comparisons should be confined to a specific caliber and the same bullet type or construction.

However, you are right in saying that the .277/110 gr TSX will perform better than the heavier 135 gr Speer - that is fairly obvious, as it is such a strongly construted bullet, that invariably retains 100% of it weight, as opposed to the Speer that may not even retain 30%, thus reducing the effective weight of the Speer to about 40 grains. What you should be comparing rather is the 110 gr TSX vs 150 gr TSX - "like with like". These bullets are so good that you may not even notice the difference on deer; you will need to go to elk and moose.

Most soft bullets cannot sustain high impact velocities, and as such, cannot compare with expanding monotithics - that is also fairly obvious.

SD is not outdated, Soft frangible bullets are.

Warrior

This is why bullet construction is much more important that SD. Which is why I chimed in on this thread to begin with. IMO, I think too many folks get hung up on this SD number, when, from what I've seen over the years, it amounts to nothing.

It IS certainly fair to compare bullets of UNEQUAL construction, because SD is derived solely from diameter-mass-weight...and THAT has been the whole argument of why some think it is SO important. If someone is so hung up on SD, then bullet construction shouldn't even be part of the equation. After all, that has been the debate of this thread right?

SD is a factor in bullet penetration right? Hasn't that been the argument?

I can't help it if I can punch holes all in it with a few quick examples of what happens in the real world where bullet construction far exceeds the irrelavence of SD.

quote:

Originally posted by Warrior:
That is why I stated clearly that comparisons should be confined to a specific caliber and the same bullet type or construction.

Well, even if we take this into consideration, with todays WELL constructed bullets, sectional densitiy still becomes nearly if not 100% irrelavent.

Take a 300 Mag and a 150 partition for a medium sized game animal like a caribou. I'll bet at any common hunting distance, say 225 yards, that bullet will pass right through both shoulders. I also believe a 165, 180, and 200 partition will all do the same.

I've seen it. And even in this scenario, SD is worthless to worry about, and is of no concern.

quote:

Take a 300 Mag and a 150 partition for a medium sized game animal like a caribou. I'll bet at any common hunting distance, say 225 yards, that bullet will pass right through both shoulders. I also believe a 165, 180, and 200 partition will all do the same.

If the above it to prove that SD is worthless, then it proves (sic) that differing momentum levels are also useless, by your reasoning. We should not confuse the killing of an animal per se with the notion that SD and Momentum are worthless. Just about anything in life can be skewed.

No single parameter can be made absolute -

- not SD
- not mass
- not velocity
- not momentum
- not cross sectional area
- not construction

they all need to be balanced in one way or the other in the most sensible way for its intended pupose, and that will vary based on the material that you work with - just lead, lead core, bonded, partition, mono-metal, etc. SD is but one factor of the greater whole.

Example; the above can be nicely balanced in say a .45-70 Govn with a hard-cast lead bullet weighing 400 grains and launched at 1,650 fps. We know its effectiveness - it has been publisized widely.

Like wise, if we need extreme penetration we will home in on "cross sectional area", as we want a non-expanding solid bullet.

If we go after large animals (African Buffalo) we will want to up the "momentum" and the mass of the bullet to get more attention in comparison with all the other parameters.

If we go for premuim expanding bullets, we need to make sure the momentum is enough to over come the "brakes" of the wide frontal expansion to still get adequate penetration, etc, etc.

If we are target shooters bullet construction is the least of our worries, and we will focus more on sleek accurately made bullets.

Lead-core bullets has its operating window; a narrow one, as they are prone to break-up.

Premium softs improve on them (the frangible ones)

Expanding monolitics are tougher and has a wider window of application.

And yes, SD can come down as we move up the scale of constructing a tougher bullet - that speaks for itself. SD cannot be viewed out of context. As stated prviously, the most sensible way is to look at the ratio of momentum over the bullet's frontal area, and even that is not perfect, as we have not fully adddressed nose shapes in Solids, ie FN vs Ogived FN vs RN.


Warrior

Does antone believe that given two identical bullets that the slower one will penetrate deeper ?.
Penetration depends on momentum. A light weight high velocity bullet will penetrate as well as a hevy one. Look at the armor penetrators they are using against tanks.
SD is not a BS concept it is a physical property. It determines the area over which the
momentum acts. That is why they put points on nails.
Good Luck!

Warrior, I'm keeping the relavence of SD to the original post.

"How will it help my shooting?"

The answer is, it doesn't. I can only assume the question is with respect to animals, because I don't think anyone cares about how much penetration occurs on a paper target.