Though I've been shooting for over 30 years, I find my mid-life
years full of more learning and curiosity for information.
So one of the topics is S.D. vs. caliber size and weight.
More specifically, I shoot 30-06 and have compared the S.D,
of the 165 and 180 gr. to smaller calibers like 25 cal, 6.5, 270, and 7mm. which in most cases have higher density than the
bigger and heavier 30-06.
With medium game it's not as big a deal, but lets consider
elk and moose size hunting. Am I going to see better killing
potential with say a 270 150gr. or 280 160gr. having S.D.s
of .279 and .283, or the slightly wider and heavier 165 or 180gr. 30-06 with S.D.s of only .248 and .271?
And the other interesting fact is all of these caliber's have
very similar ftlbs of energy at 100-200 yds, so about the same
"hitting power", but differing weights and densities.

Hoping this makes an interesting and informative post.

Aceman.

Use a TSX and it won't matter which you use

SD usually implies a higher BC, meaning better exterior ballistics at long-range, but the most important thing that comes from a high SD is straight and deep penetration. The bullet can expand further back on the shank before it becomes a "pancake".

Sectional Density (SD) boils down to the length and weight of the bullet in relation to expansion of the bullet during penetration. The longer and heavier the bullet the more time it has for expansion and the slower it expands the more penetration you get because your pushing a smaller surface, thus you get more penetration as it expands slower..The cross section of the expanding bullet slows the bullet down and stops penetration therefore the slower it expands the more penetration you get..

I suppose you could and should add to this scenario that the longer a bullet is the better it holds its velocity at longer ranges all things even steven..so a longer, heavier bullet of the same shape will normally shoot flater over very extended ranges because it holds its velocity better than the lighter bullets that lose velocity quicker..Thus supposedly, a 200 gr. 30-06 starting at 2600 FPS will maintain velocity better than a 150 gr. starting at 2900 FPS over say a 600 yard range, therefore the 200 gr. bullet will shoot flatter at extended ranges.

This is an over simplification, but it about says it all..Keep in mind that penetration is the first and foremost important aspect of any bullet because if it does not get in there and do its job then it will fail.

Folks can get totaly anal over these things, but in the real world, most of it is just entertainment for young men that are eaten up with technicalities of balistics, love to discuss the pros and cons, and it has far reaching serpintine arms of confusion and myth, and it takes years to come back down to reality and admit its probably all BS to start with, but it was a fun trip..:)

how is SD applied when you shoot 'em in the neck?

Sectional density is simply the ratio of the weight of the bullet to the cross sectional area of the bullet. Thus, all bullets of the same caliber and weight will have the same sectional density. Given bullets of the same caliber but different weights, the heavier the bullet the greater the sectional density. Given bullets of different calibers but the same weight, the smaller caliber bullets will have the greater sectional density. Sectional density is probably only valid as a predictor of performance when applied to bullets of the same construction and form.

Ballistic coefficient is used to predict ballistic performance and is a product of a number of aspects of a bullet's form which affect the way the bullet moves through air. Given two bullets which have the same form (same caliber, same ogive, same base) but different weights, the heavier bullet will have (incidentally) a greater sectional density (because it's heavier) and a higher ballistic coefficient (because it's heavier and longer.)

Ace,

I look at SD & BC like this:

SD describes the penetration characteristics of a bullet. So, the higher the SD the better the penetration theoretically.

BC describes the flight characteristics of a bullet. Meaning, the greater the BC value the flatter it will shoot and it will experience less wind drift.

I look at it this way, because the math behind simply gives me a headache.

This is why many shooters like to use heavy for caliber bullets like 200gr .30 cal, 175gr .284 cal, 140gr .264 cal, especially if you live and hunt in places where you can shoot a long way.

CLB

i say keep shooting your 30-06 (with a good bullet) and don't sweat the small stuff. no telling how many elk/moose (and everything else on the planet) have been taken with a 30-06. while there clearly IS a difference in sd and bc between bullets, at the "usual" hunting ranges, neither matter a great deal.

you leave out the fact that the .30 caliber bullets do not stop at 165 grains... the highest sectional density commonly available in a hunting bullet is the 220 grain .308 bullet...

if construction is similar, a higher sectional density may indicate the ability to penetrate deeper

sectional density is simply the relationship of weight and diameter... the sectional density of any diameter bullet can be increased by increasing its weight...

many newer mono-metal bullets made of copper or gilding metal rely far less on sectional density to achieve desired penetration, than standard jacketed lead bullets...

around the time that my oldest child was born i loaded some .308/220 monolithic solids for my 30-06...
just in case i needed to drop one of those rogue northern illinois elephants, ya know...

Ringworm,
With good SD you get two holes, with bad SD you get one hole, can't get any plainer n that. With real bad SD you get a blow up on the skin and I have seen this more than once.

SD is irrelevent to expanding bullets and construction can blow holes in any argument.

An 85gn TSX will out penetrate a 100gn Cup and Core 6mm even though the SD is higher with teh heavier weight. This repeats right up teh line to any caliber where a lighter weight (shorter) bullets has superior integrity of design.

The whole argument is pointless unless you are talking solids and dangerous game, even then, mono metal Vs Steel jacket Vs naval bronze Vs round point Vs flat point and on it goes.

JW

SD is a function of bullet weight and non-expanded diameter. It is not a measure of terminal performance, such as shooting them in the neck. Any two bullets with identical diameters and identical weights will have identical SDs regardless of their construction or how they penetrate.

Having said that, bullets of higher SD do tend to penetrate deeper in game animals for two reasons: 1- Higher SD means greater weight, which means lower velocity, which means slower and/or less overall expansion, drag, and "hydraulic effect"; 2- Greater weight means more momentum.

-

That really depends on the construction of the bullet...

Because with an expanding bullet, the cross sectional area and weight (usually) change, thus SD changes during terminal ballistics.

There are a couple of guys down the road from here who seem to kill a lot of deer and I don't think either one could define sectional density if it were sitting on his kitchen table. Man, you just have to wonder how some of these guys get by in this world...

I respectfully disagree.

SD does count - with expanding bullets, as well as solids. The only "if" is - IF the bullets are of the same type. Even with an all-copper bullet like the TSX - the one with the higher SD will penetrate further than the one with less SD.

Based on my own back-yard tests (and only comparing bullets of similar brand) the SD number does give one a pretty good idea of how far the bullet will penetrate - even when comparing bullets of differing speeds and caliber.

Therefore - the arguement, or discussion is anything but pointless.

There is a reason (even when looking at expanding bullets) that the 6.5 Swede with it's long high SD 160 grain bullets, the 7mm Mauser with it's long high SD 175 grain bullets, and the 30-06 with it's long high SD 220 grain bullets developed such a great reputation on killing game larger than their caliber might first indicate.

It was because of the great SD these bullets all carried - even though they were all designed to expand.

I do however agree that it would be a meaningless number when comparing bullets with different expansion characteristics. SD is only useful when looking at bullets of similar construction - whether they be soft-points, hard-points or expanding all-coppers.

Thanks for the replies on S.D. and it seems to be a combination
between good penetration and controlled expansion. But what about a bullet with maximum penetration and high S.D. without good expansion?
All the respected gun writers agree that expansion along with
penetration is what kills, creating a wound channel causing
internal devastation of tissue, as long as you get to the vitals.
So do I trade some expansion for more penetration and higher S.D.
or a little less S.D. and penetration, for good controlled expansion?

Aceman.

aceman,
You make that judgment by what animal your shooting, mostly on size..On a Moose or Alaskan bear I want SD and its penetration. On a deer or pronghorn antelope, I'll take expansion..but moderation is the word for success, and just too many folks go to the extreme in either or both directions..

SD, velocity, penetration, expansion and a host of other coined terms boil down to one component and its the one that works best.."common since".

And that statement explains exactly why bullet construction also matters. A good controlled expansion bullet retains its mass with limited increase in diameter (i.e. it retains its SD) while a varmit bullet will lose much of its mass while expanding drastically.

Do you think those guys could explain how gunpowder is manufactured? Does that make it more or less important?

Two good posts;Ray's ,too.They illustrate why numbers don't tell the whole story....they are just the start,a reference and not much else.You really can't pick a BG bullet by just reading ballistic tables.

I don't know, I tried to talk to them about burning rate once and they just looked at me like I got off a spaceship from China. And they keep right on killing deer.

Brian,
Thank you for the courtious dissagreement.

Let me explain this another way:

We all read the reviews in RIFLE when the 130 grain TTSX .308 caliber bullet was introduced and trialed in Namibia, with a range of rifles and velocities and saw the penetration reported on game up to Kudu. No surprise there.

We all agree that the SD of any 130gn .308 bullets would be considered inadequate for plains game if using conventional bullet construction. This means that the penetration acheived, irrespective of SD for the aforementioned bullet would compare favorably with a conventional bullet of much heavier weight. It therefore negates SD from the comparison wouldn't you say?

On another note, when I was an SCI President, I met a hunter with International experience that used as his standard load, a .300 Winchester Magnum with a 130gn X bullet. He claimed he never recovered one and never found a need for a heavier bullet.

JW

FYI, I break all my own rules when I select bullets for different cartridges. I would load a 220gn Woodleigh Weldcore in a .30/06 but never load one in a .300 Magnum. I would load a 130gn TTSX in a .300 Winchester but not a .30/06. It has to do with where I would use the rifle and on what game, rather than any traditional logic.

No. Each bullet has a sectional density, inside the animal or not. The notion that high sectional density aides penetration is still a truism, expanded bullet or not. I think you may be hung up on the sectional density given for each unexpanded bullet. You understand that the condition of the bullet changes upon impact and are throwing out the "baby with the bathwater", so to say. A thirty cal TSX bullet of 180 grains that has expanded to 0.85 inches inside the animal has a higher sectional density than a 180 grain TSX that has expanded to 1 inch, thus will penetrate more deeply. SD still is a measurable factor in determining penetration.

Good day.

I was trying not to be picky/anal on this subject, but it may be informative to clear up some of the "sloppiness" in this thread. Most of you guys know this stuff, but it may cause some confusion to use the wrong terms. "Caliber" is not used to determine SD. Bullet diameter is used. A .308 Winchester is a 30 caliber, which is actually 100 times the bore diameter, without the label of "inches." The diameter of the bullet is closer to groove diameter; 0.308 inches in the case of the .308 Winchester with most jacketed bullets.

Also, the "cross sectional area" of the bullet is not used in the equation, although I think it would be more useful than the simple use of diameter squared, which is used. If the cross sectional area were used, the equation would be:
Bullet weight in pounds/cross sectional area in square inches = SD = wt/Πr2 (dang superscript doesn't work for me), or Sectional Density equals weight/pi x squared radius. However, the true equation for Sectional density is the weight of the bullet in pounds divided by the square of the bullet's diameter, in inches; or wt/squared diameter. The squared diameter is actually the area of a square, not a circle, mushroom, x-bullet, etc.. The length of the square's sides is equal to the diameter of the bullet; the expanded diameter or not.

Whew! Got that off my chest!

I wanted to thank everyone for the comments on trying to
understand how S.D. works with bullet weight and diameter.
It would appear that S.D. is important for bigger game, but
not the only element in the formula. But after doing some
comparisons, I find that it's not always that the heavier
and bigger diameter gives you the highest S.D.
A .25 cal. 120gr. is smaller than the 6.5,270 and 7mm bullets,
but has a S.D. of .260, but yet the bigger and even heavier
270 130gr has only .242, the bigger 7mm 120 & 140gr has only
.213 and .248. Even the 6.5 at 120gr has a .260 S.D.?
So if I were to hunt elk or moose, would I have more killing
ability shooting in the some spot with say a 25-06 120gr with a
higher .260 S.D. or a bigger bullet like a 270 130gr with a
lower .242 S.D. or a 7mm 140gr. with a .248 S.D.?
My concern is when do we trade bullet weight and size with a
lower S.D., for a lighter bullet with a higher S.D.?
This is only a concern with bigger game like elk or moose at
medium range, not deer etc., since I'm trying to find a second
rifle caliber that will give moderate recoil, but anchor deer
size to moose. Since a .243 will take all deer size game out
to 200-300yds. with mild recoil, but doesn't give me total
confidence if I encounter bigger game.


Thanks, Earl.

Interesting post as I'm also looking for a second rifle and
caliber that is somewhere between the 243 and 308. I want mild tomedium recoil comfortable for my young boys, but can handle elk and moose at close range if the opportunity came up.
I've been using the 30-06 for years in both 165 and 180gr
partition, but don't want something too close to it.
The 243 is light and easy to shoot, but not totally confident
if we came upon larger game, 308, 270 and 280 seems too close
to the 06 especially in recoil. So I'm looking at 25-06, 6.5's
260 or 7mm-08, but I don't reload so rifle and bullet choice
is very important. Now this S.D. topic may play a part since
25's and 6.5's have as much or more than the slightly bigger
bullets, so for all round shooting from deer to elk with one
bullet weight will I have more ability with a 115-120 gr. 25cal
or a 140gr 7mm-08 partition, since they have similar S.D.'s
but the 7mm is slighty heavier and bigger cal.?

elderstatesman,

If you go with a .25-06 and use 100 TTSX you will just about do everything with it you .30-06 will do. You get about four feet of penetration in elk with that bullet.

There is a post made yesterday why I ordered a .257 Weatherby. It addresses this caliber and bullet.

Of the calibers and bullets mentioned,I'd be inclined to take the 7/08 and a well constructed 140 gr bullet.With bullets being so close in weight and caliber,bullet construction will be far more important than SD numbers on a chart.

Mr. Atkinson,


Me thinks you are missing the argument posted by the majority here, that it's SD AND BULLET CONSTRUCTION that must be taken into account. As you so eloquently posted above. Construction matters as much as SD. I believe it to be 50-50.

It would otherwise be like comparing apples to oranges. But for the most part I think we all are on the same page. SD and CONST. vs SD and CONST. Apples to apples. NO more......no less. Give some of us the credit and ability to know the difference from one SD bullet, amongst the many different types of bullet construction. I go for SD every time with a properly sized for game bullet construction every time. Has worked for over
30 years. But I'm not saying I can't still learn something new.

I would not compare a Sierra Match King with a Nosler Part.
Nor do I believe would you.




Best regards, Bob