Given two similar calibers (say 7mm STW and 300 Win Mag) with the same amount of energy and similar bullet construction, which would penetrate tough game better. A 154 grain 7mm bullet with a higher sectional density, or a 165 gr .30 cal bullet. There are a number of factors involved here and a definitive answer might not exist. Does anyone know if any of the bullet manufacturers keep this kind of data when they develope bullets? Does anyone have some personal experience that might shed some light on this subject?

Bullet construction is probably the single most important factor, above and beyond weight or sectional density.

Isn't that the question!?! The two play hand in hand, that's for sure. If we look at a slightly different example: Let's say we have two 1-ounce chunks of lead and one looks like a round ball and the other looks like a drill bit - it is obvious which one will penetrate better. The less frontal area there is to impede the progress of the full weight of the projectile, the better the penetration. The shape (sectional density) plays the major role, imho.

Now, if we take some weight off the drill-shaped piece, the answer is not so clear. The round ball will have more weight, but the other piece will have less resistence (and now less weight to drive it) - again, sectional density calculations will provide the answer. That's the way I look at it, anyway. Anyone else??

In the specific case you mentioned, it's a real tossup. Depends more on how the bullets are constructed, I would think. (I'd use heavier .30 cal bullets than those 165's for tough game anyway, which would also boost your sectional density). maxman

It was already stated that the bullets are of similar construction. For the sake of argument, let's say they are both nosler partition semi spitzers. At the point of impact, they are both traveling at exactly the same velocity. Given the above conditions, the bullet with the higher sectional density should give better penetration.

Also, as was stated by the previous poster, if you change the bullet weight, you change the sectional density.

[ 12-03-2003, 21:31: Message edited by: Clement ]

I would assume that the two bullets mentioned (assuming they are both the same type of bullet) should have similar pentration. Heavier projectiles retain their velocity more effectivley. I would think that the slightly higher weight would somewhat offset the sectional density advantage of the 7mm round. The .30 bullet would have a larger wound channel due to its larger size. Does this seem reasonable?

In response to the comment about using heavier bullets, I realize that the 180 gr bullets will penetrate better, but I prefer the higher velocity, flatter trajectory, and lower recoil of the 165 grain bullet in my 300 win mag. I shoot 165 Hornady Interbonds with good results on Elk. I am considering switching to a 7mm STW with 154 Interbonds (for flatter trajectory, higher retained energy, and less drfit due to wind) but don't want to give up penetration.

I would say about the same btwn. the 7mm/150grNP & .308/165grNP @ the same vel. A 7mm/160grNP @ 2800fps pentrates a bit better than a .338/210grNP @ 2700fps. This is based on my own tests in wetpack. A larger frontal area will slow penetration whether by expansion or bullet dia.

The SD (smaller caliber) is going to mean more than BC (heavier bullet) when you hit the animal.
Retaining energy in air is lot easier than in meat and bones. The difference is exponential.
But there's only one way to find out.
Either one, placed well at adequate velocity....

"Similar" is often not close enough. It is generally not "apples-to-apples" to compare SDs across calibers; larger bores are generally used for larger game and so, I would conjecture, are manufactured with slightly heavier jackets for a given section density.

Some calibers have many magnum rounds, while others do not. For example, the 338 bore is almost entirely magnums (save the 338-06), and so I would suspect its bullets are optimized for the corresponding velocities. On the other hand, (American) bullets for the 358 bore are probably married to 35 Whelen velocities, and are jacketed accordingly.

Test them out, it's the only way to know. Same goes for ballistic performance, drop, wind drift etc., reality can sometimes divergence from book facts in surprising ways. I saw some penetration test results once that found that the 338 bore Nosler 200 gr ballistic tip out-penetrated the 210 gr partition!

I seem to remember BOB HAGEL reporting that the 175grain Nosler in a 7mm Mag. gave deeper penetration in Game than any of the other Nosler Partitions regardless of caliber.
However he also pointed out that the wound channels were smaller than the larger bores.
For Elk and up he seemed to perfer the 338 Win Mag and the 340 WBY.
His books have a lot of very good info.

Of two similarly constructed bullets and out of the same rifle, the one with the highest SD has the potential for better penetration.

The site below has bullet SD's for most calibers:

http://www.woodleighbullets.com.au/Bullets.html

You no kin drive a spike wid a tack hammer!

Higher sectional density will give a higher weight bullet in that caliber anyway.

Sectional density and then bullet shape or construction is the next thing I look for ( Like being a Round Nose, then Semi Spitzer next, then Spitzer and Boat Tail Spitzer last).

Of course some of the premium bullets might perform better, but a high sectional density RN, SSP or Sp is normally going to do a good job, and may negate the need for the premo bullet.

Okay - here's a related question. Assuming for the sake of argument that all other variables are equal (bullet construction, velocity, resistence of target, etc), is it true that bullets of equal SD will penetrate equally?

What I'm getting at is this: would comparably constructed bullets of, say .243 and .338 penetrate the same distance if they hit the same medium at the same velocity?

Seems to me they would, but that just doesn't feel right ...

Brian

Sectional density of the 100 grain .243 bullet, the basic max-weight for that caliber, is only .242 but the 210 grain .338 bullet which is on the low side of that caliber has an SD of .263. The 250 grain .338 bullet has an SD of .313.

The answer is yes.

If a .243 bullet and a .338 bullets had the same sectional density and velocity (and if they had the same 'construction," however that is measured, and kept their sectional densities the same during expansion, then, yes, they would penetrate equally in a "fluid."

However, most .243 and .338 bullets are not made with the same "construction," and game animals are not fluids. The .338 might crack a bone and go through whereas the .243 might not.

The theory works only if both bullets are heavy solids. Old time elephant hunters could penetrate elephant skulls with a 7mm Mauser 175 grain solid just as well as with a .470 Nitro Ezpress 500 grain bullet. But the .470 was a better choice because, if you missed the brain, it would deliver much more shock to stun or turn the elephant.

BLOC:

Nice town you live in, been there often.

Seems to me Brian, that they should if the media is comparable. However as Indy suggests, I would trust a bigger bore bullet when hitting bone over a smaller bore, if the game is elk or something.

For these little bitty blacktail, I don't really think it matters. As pointed out tho, 338 bullets of 200 grains or more have a sectional density of .250 and up. A 105 grain 243 bullet has a sectional density of about .250.

Interesting thought, but match the bullet to the game and rely on proper shot placement, and then it is really just an academic question at that point. Ask any of our resident "experts" with a lot of text books on the shelf, a 243 will not kill Elk. There has " never " been an Elk ever killed with a 243, regardless of shot placement.
All the people who say they killed an elk with a 243 are lyers. ( At least according to them!)

Bwana just a note, BC has little to do w/ penetration (under 200yds anyway) as it is the measure of the bullet shape. A boat tail adds to the BC but not to the bullets ability to penetrate except that it allows the bullet to hold onto it's vel. @ longer range (over 200yds).
A bullets ability to penetrate has alot more to do w/ construction than weight, ie Barnes 'X' or solids.

[ 12-05-2003, 20:05: Message edited by: fredj338 ]

...just use a mono bullet like the Banres X and be done with it!

Construction means alot in the penetration game!The larger the frontal area means less penetration but pushes more tissue in front of the bullet =more destruction.Given a choice I would always take more bulletr diameter and feed it a bullet to penetrate.

This could be an interesting experiment with 6.5, 270 and 7mm as you could probably get real close to matching SD in all three calibers and could handload to match velocities.

I think some are missing a point, weight and SD pretty well go hand in hand, you must have one to have the other all things being equal...A bullet 3 times its cross section is heavy indeed and has a world of SD.....That is the criteria the old elephant hunters used.

The figure of merit is the BC in tissue of the expanded bullet. The trick is figuring out what that BC will be...

Bullet construction determines how a bullet opens at a given impact speed in a given tissue. How it opens includes the diameter and the nose shape of the expanded bullet. Construction also determines how much of the original weight is retained. Increased diameter lowers BC (but increases wounding); a blunter expanded profile decreases BC (but increases wounding); and lost weight decreases BC (but can increase wounding, especially at high speed).

The type of tissue first hit affects all 3 just mentioned.

All bullets of the same expanded SD are not the same. The skinny ones are less stable and more prone to tumble.

On the whole, it appears to me that bullet mass is the figure of merit, so long as bullet construction is kept in line with it. The goal is to have enough diameter to do the damage you want and enough mass to move that diameter through to the depth you want. For a given animal, the diameter is the same, so it's just mass that determines the depth.

Another way: a 220 gn .30 should about equal a 220 .45, but the .45 has to be constructed to hardly expand and the .30 has to manage to greatly expand while holding together. The designer of the .45 bullet has the easier job.

ASDF,
Sounds good but just isn't the way it works a 220 gr. 45 and a 220 gr. 30 caliber are not in the same ball park any way you cut it...In the 220 gr. 30 caliber you get expansion and have a long shank pushing that bullet forward as it expands..

The 45 cal 220 expands but only has a little bit to expand then the shank is gone and penitration stops cold, nothing to push it...

To go a step further, a 220 gr. 30 cal. solid will penitrate much deeper than a 220 gr 45 caliber. A 220 gr. 30 cal. soft will penitrate deeper than a 220 gr. 45 caliber solid....

To get any penitration at all on big tough game one must have at least a 300 gr. 45 cal. and 45 or 500 is best. I would not shoot a Buffalo or elephant with a 220 gr. 45 cal of any construction, but I would with a 220 gr. 30 cal. solid or soft. perhaps only a solid on elephant.

If I read you properly you think a 220 45 will do the same thing as a 220 30 cal on say dangerous game, and nothing could be further from correct...

[ 12-07-2003, 05:15: Message edited by: Atkinson ]

Hello Ray,

Yes, I didn't get my point across. A .30 220 SN might expand to, say, .50. For the .45 220 to expand to the same .50 would require a bullet of different constrution. As I stated in my earlier post, I believe it is easier to design the .45 to expand 11% to .50 than it is to get a .30 to expand 67%. The .30 will likely loose 10-20% (or more) of its weight in trying to get to .50. The .45 would likely loose none (to get such limited expansion, all copper constrution would be needed). In the end, you have a .50 RN or FN plowing along with only 220 gn at most behind it. Again, I think the .45 will win simply because it will likely have retained more weight.

The 220 solid example you give missed my point as well. My claim is that the BC (or SD, if you assume the same final nose profile) of the expanded bullet is what counts. A 220 .45 cannot contract to .30 cal on impact. It will surely penetrate less; it has twice with frontal area (and drag in tissue) yet no more momentum/mass to carry it through.

As for 220 gn .45 vs .30 on dangerous game, again, we would be comparing basically a .45 solid (probably an FN) against a .30 SN. With both ending up at the same diameter, the penetration will be the same. THERE IS one big difference. The .30 SN could be a Partition which has the option of shedding its nose and continuing on as a .30 FN solid. Such expansion+shedding seems to be praised by all who use them.

I don't think I'd care to poke a buffalo (never tried it) with only 220 gn of anything. I'm not sure what a .45 220 solid would have to be made of to endure impact at the speeds a 220 .30 can be delivered. It'd probably have to be paper patched steel (such things were tried in the 1800s).

Steel bullets? I have taken this discussion away from the original poster's "similar bullet construction" proposition. And I certainly didn't want to argue with you; your hunting experience is about 3 orders of magnitude beyond mine. Still, once the bullet is in the tissue, divide the final frontal area by the final mass and you'll have the relative penetration ability. A bigger animal needs a bigger final diameter and so to get the penetration, more mass is needed -- or one could say, heavy animals require heavy bullets.

Karl

[ 12-07-2003, 10:31: Message edited by: asdf ]

Karl,

A couple of thoughts if I may.

You are of course right that BC after impact will determine penetration.

However, the 220 grain 30 does not expand instantly and as such will have a much higher BC for some of the penetration than does the 220 grain 45 non expanding bullet.

This in turn could mean that by the time the 220 grain 30 calibre has expanded to 45 it has reached the insides of the animal and is travelling much faster than the non expanding 220 grain 45.

By the way, the above can be demonstrated to some extent on smaller animals like kangaroos , goats and pigs. My belief is that bullets like the 375 300 grain Hornady and 500 grain Hornady from the 460 Wby probably don't do much more than have the nose of the bullet flattened on impact with roos etc. However, when measured across many years and countless animals the 100 grain and 130 grain 270 can't equal them.

The reason. I think the 375 and 460 while having a lower impact speed than the 270 travel through th animal at much higher speed.

In other words it is a case of frontal area and velocity while travelling through the animals. For that, I think a 220 gran 30 that expands will beat a 220 grain 45 calibre non expander.

Of course on smaller animals there is no doubt that the initial impact of a large calibre flat nose has a huge bearing on the outcome. However, I am not sure that would apply to animals that weigh 1000 pounds and more.

Mike

[ 12-07-2003, 11:50: Message edited by: Mike375 ]

If you had two bullets, solids, one made of copper, the other a FMJ. Both of exactly the same weight, caliber and shape, would the longer copper bullet penetrate more?

[ 12-07-2003, 17:32: Message edited by: John Y Cannuck ]

ASDF,
I know where you are coming from and technically you are correct, but in reality one has to realize that the 45 caliber 220 would most certainly tumble and penitration would stop...and if any bullet is excessively long the same will take place.

The old African poachers said that a bullet should be 2.5 or 3 times its cross section in length (can't recall which number is correct) and that is as true today as it was then IMO..
Good examples are the 175 gr. 7mm bullets, 160 6.5 bullets and yes I suspect the 220 gr. 30 caliber falls neatly into this hall of honor.

All right, Mike375, you put a dent in my nifty theory. I very much see your point: while the .30 is transforming itself from a spitzer .30 to a .45 RN, it is doing so in tissue -- namely hide and muscle -- which doesn't really need to be crushed. The .45 solid is slowing more rapidly in this non-vital tissue.

Your comment on the .375 vs the .270 goes with my argument. There is wide spread agreement that above a certain speed, a bullet's passage causes significant tearing in the "temporary wound cavity." It stands to reason: the bullet shoves tissue aside, and if this lateral motion is fast enough, the tissue's elasticty can't contain it without tearing. The wee .270 will slow about 3 times as fast (having 1/3 the mass) and soon be only effective at crushing the tissue at its nose.

Ray, I'm not convinced my hypothetical 220 .45 will tumble more easily than an expanded .30. Indeed, I suspect it is less likely to do so. I've never read of a handgun hunter reporting such bullets to tumble. Perhaps the higher fps of the rifle has an effect, but I'm skeptical. The expanded .30 has less of its mass out at that .45 diameter, and that can only make it less stable.

That poacher's relationship of length/bore may have been for solids. The numbers you give are right for the .45/500. The .30/220 has a ratio of about 3.9 and the .284/175 is about 4.2. I do suspect the .45 solid is the more stable of these three.

Finally, JYC, I'll hazard a guess that the copper and the steel solids will penetrate to exactly the same depth, unless the longer copper job tumbles.

OK, enough words from me...

Karl

The term "sectional density" is in effect a way of characterising the weight of a projectile in relation to it's diameter; it is a means for comparing the probable penetration qualities of two identically constructed bullets of different diameters, with the bullet having the higher sectional density being likely to penetrate more in the same medium, if both strike at the same speed. Additionally, if a .308" bullet and a .375" bullet having identical structure and sectional densities strike a test medium at the same velocity, it is reasonable to expect them both to penetrate the same distance even though the .375 bullet is heavier!

Sectional density is the weight of the bullet in pounds divided by the square of the bullet's diameter in inches. It has nothing to do with the bullet's shape at all! A .308" diameter, 220-grain slug with two flat ends has the same sectional density as a .308" diameter, 220-grain slug that is pointed on one or both ends!

IF the bullet construction is identical (cannot compare solid copper to copper and lead) and IF the impact velocity is identical, and IF the media is identical, THE BULLET WITH THE HIGHEST SD WILL ALWAYS PENETRATE FARTHER. The greater weight advantage of the 30 caliber bullet (of the same SD as a 28 caliber) is negated by the larger resistance of the greater mushroom of the 30 caliber.

In reality though, it may be difficult to actually know if the 154 7mm is of equal construction to the 180 30 caliber, as their jacket thickneses and core hardness may vary. In addition to the requirement for identical construction, the bullets must hit at the same velocity and precipitate a mushroom at exactly the same rate. Bullet testing in the same media is the only sure thing that gives the controlled circumstances to make an equal comparison.

I think SD is best summarized as a way to measure the POTENTIAL of a bullet to penetrate, if given the right construction for the task.

[ 12-09-2003, 17:12: Message edited by: Thunderstick ]