Bullet diameter vs sectional density vs energy

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tommy88

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Could somebody explain to me how all these factors work together to kill an animal. I've always used energy in ft lbs, but it turns out there's more to this equation. I should also add that I'm not a long range guy, so I'm not too interested in Ballistic Coefficient.

For example: would a 7mm rem mag with a high SD be better or worse then a 338 win mag with a high diameter. I know its a difficult argument because they produce different energy, but you get the point.

270 vs 35 whelen, 243 vs 308 etc......

I know theres more to this; recoil, wind drift, trajectory and whatever else, but is there a relatively simple solution to understanding all of this in terms of "killing performance".
 
Higher sectional density, assuming similar bullet construction, will mean greater penetration. A 150 gr 7mm bullet, fired out of a 7x57 or 7-08 is adequate for anything up to moose. A 150 gr .35 cal bullet is a pistol bullet.

A heavy bullet with the same sectional density as the lighter one will have a slight edge because it will have more momentum. A heavy fast bullet will be more effective than a light fast one, but there's a price in recoil.

As a general rule, light, fast bullets kill faster than slow, heavy bullets, but you get more bloodshot meat.
Slow, heavy bullets are reliable, but not spectacular killers, but damage less meat.

Energy, in itself, doesn't mean much.
 
9.3mauser said:
Higher sectional density, assuming similar bullet construction, will mean greater penetration. A 150 gr 7mm bullet, fired out of a 7x57 or 7-08 is adequate for anything up to moose. A 150 gr .35 cal bullet is a pistol bullet.

A heavy bullet with the same sectional density as the lighter one will have a slight edge because it will have more momentum. A heavy fast bullet will be more effective than a light fast one, but there's a price in recoil.

As a general rule, light, fast bullets kill faster than slow, heavy bullets, but you get more bloodshot meat.
Slow, heavy bullets are reliable, but not spectacular killers, but damage less meat.

Energy, in itself, doesn't mean much.
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This plus frontal area.
The larger diameter bullet will impart more energy when it hits the animal, than a smaller bullet will.
A great demonstration that I witnessed first hand years ago was between my 7mm Rem Mag with 165 gr ammo compared to a 338 Win MAg with 200 gr bullets on a large boulder buried in a stream bank at more than 100 yards. A good comparison, as both use the same case, for a more equal comparison (as opposed to a300 WSM and say a 338 Ultra Mag with a much larger case capacity). Another good comparison would be a 25-06 compared to a 35 Whelen.
The 7mm smacked the boulder with a sharp crack and sent a splinter of rock flying.
The 33Win Mag, with a mild handload, whalloped that boulder and shifted that boulder in the bank.
This is why there is a dramatic effect on large, heavy game (larger moose, large bull elk, big bears, bison, etc.) that is experienced with the larger calibers, as compared to the smaller calibers.
 
Sectional density is essentially meaningless in this day and age. When all bullets were of similar construction it may have had some validity, but not any more.
All bullets of a given weight in the same diameter have the same sectional density, and do not factor in bullet construction. Example, a 50 gr vmax and a 50 gr TTSX have the same S. D., but one of them will penetrate a$$hole to eyeballs and the other might not make it more than a handful of inches deep. One of those bullets will kill any deer on the planet from any angle, the other is a gopher and coyote bullet.

Bullet construction and retained velocity (BC) and rotational velocity play more into it than “energy” or sectional density.
The bullet itself matters much more than the cartridge case that started it on its journey when it comes to killing.
 
There are enough variables in this equation to give a mathematician a bad case of brain cramps.
Sectional density matters, until it doesn't matter so much if the bullet fragments on impact. Width of the frontal area/expansion matters and when that expansion occurs matters too.
I agree that energy is an incomplete measurement of killing ability, and is over-represented in peoples choices.
Momentum is seldom considered by most hunters, but is very important if penetration is critical, such a when shooting a solid non-expanding bullet through an elephants skull bone.
Bullet construction and placement are the most important variable of all.
Bullet fragments sometimes help kill smaller animals like deer quickly when their small fragments hit stuff like nerves and blood vessels that otherwise would remain intact.
Bullets that don't fragment at all do better in really big game because they always penetrate deeper than the fragmenting types, and are more likely to break big bones and keep going.
That's why there are popular bullets that are combinations of fragmenting / penetrating type - Nosler Partition, RWS TUG, Cutting Edge Raptor etc.
And some prefer almost no fragments but wide expansion and moderate penetration - Norma Oryx, Nosler Accubond, etc.
And some prefer Deep penetration with no weight loss and no fragments but accept the trade off of a narrower wound channel - Barnes TSX, Lapua Naturalis, Nosler E-Tip, etc.
And some prefer full fragmentation and quick energy transfer - Berger Hunting, Hornady SST etc.
And many like somewhere in the "middle" and use traditional bullets that mostly fragment but are somewhat reinforced like the Remington CorLokt and Winchester Power Point.
I use and like most of them in different situations. It's nice to have choices. If stuck with one type for everything, I'd choose a medium weight for caliber, bonded, lead core bullet for all my hunting and not complain. Norma Oryx or Nosler Accubond come to mind. 160's in 7mm, 165 or 180 in .30 cal, or similar. Different choices might be appropriate for African game or other exotic pursuits.
 
9.3mauser said:
Higher sectional density, assuming similar bullet construction, will mean greater penetration. A 150 gr 7mm bullet, fired out of a 7x57 or 7-08 is adequate for anything up to moose. A 150 gr .35 cal bullet is a pistol bullet.

A heavy bullet with the same sectional density as the lighter one will have a slight edge because it will have more momentum. A heavy fast bullet will be more effective than a light fast one, but there's a price in recoil.

As a general rule, light, fast bullets kill faster than slow, heavy bullets, but you get more bloodshot meat.
Slow, heavy bullets are reliable, but not spectacular killers, but damage less meat.

Energy, in itself, doesn't mean much.
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Funny thing; I sort of agree with everything you said but I'm going to split a very important hair with the part I bolded. While energy by itself doesn't mean much, energy transfer is practically everything. Last time I was having beers with Sir Iassic Newton, he did one of those nod nod wink wink things and told me that nothing much has changed. Work still cannot be done without the transfer of energy. He didn't know much about bullet construction. but being sort of an agreeable bloke was quick to point out that different bullet construction was just a way of manipulating the time and space that the energy was being transmitting the energy in. That guy doesn't lose many arguments, so I thought I'd just let him have that one. Good guy, no fun at parties.
 
The sectional density that really matters, is the sectional density as the bullet passes through the media. If the bullet expands more, the sectional density drops, if the bullet fragments, the sectional density drops. So unless you are using non expanding bullets, comparing the sectional density of unfired bullets, is a flawed comparison.
 
stubblejumper said:
The sectional density that really matters, is the sectional density as the bullet passes through the media. If the bullet expands more, the sectional density drops, if the bullet fragments, the sectional density drops. So unless you are using non expanding bullets, comparing the sectional density of unfired bullets, is a flawed comparison.
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Sectional density is a big deal with solids, but unless you're hunting elephants with novelty weapons it's sort of a non-issue. That #### got worked out more than 100 years ago.

On more ordinary game, with decidedly ordinary calibers people are their own worst enemies. Its pretty easy, most calibers have sort of standard range of weights in bullets. Use the light ones on the light animals, and the heavy ones on the heavy animals. Going a bit farther; it makes sense to use the soft bullets on the soft animals and the hard bullets on the hard animals. Short of thick skinned, not much is hard. Guys get into trouble by pushing things to extremes. Most people with an IQ higher than room temperature know that hunting buffalo with a 22/250 and gopher bullets is a bad idea, but oddly they might think that something that would be a first class choice for a buffalo should be awesome on a stupid whitetail.

Stay away from the extremes, pick a middle of the road approach and just go hunting.
 
Well let's do a simple apple's to apples ( if that's at all possible).

Hypothetically, let's say that we are using exactly the same gun, with exactly the same bullets (let's call it barnes ttsx) and we're loaded pretty hot. Between a 7mm rem mag anda 338 win mag, which would kill a trophy sized wood buffalo at 200m (or charging kodiak at 20m) more dead?
 
Dogleg said:
Sectional density is a big deal with solids, but unless you're hunting elephants with novelty weapons it's sort of a non-issue. That #### got worked out more than 100 years ago.

On more ordinary game, with decidedly ordinary calibers people are their own worst enemies. Its pretty easy, most calibers have sort of standard range of weights in bullets. Use the light ones on the light animals, and the heavy ones on the heavy animals. Going a bit farther; it makes sense to use the soft bullets on the soft animals and the hard bullets on the hard animals. Short of thick skinned, not much is hard. Guys get into trouble by pushing things to extremes. Most people with an IQ higher than room temperature know that hunting buffalo with a 22/250 and gopher bullets is a bad idea, but oddly they might think that something that would be a first class choice for a buffalo should be awesome on a stupid whitetail.

Stay away from the extremes, pick a middle of the road approach and just go hunting.
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I have it agree with this approach. It doesn't have to get complicated, yet ,many of us do complicate things to the point that a new shooters and hunters I talk to think you need to have a math and physics background to properly pick a bullet.
Cat
 
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tommy88 said:
Well let's do a simple apple's to apples ( if that's at all possible).

Hypothetically, let's say that we are using exactly the same gun, with exactly the same bullets (let's call it barnes ttsx) and we're loaded pretty hot. Between a 7mm rem mag anda 338 win mag, which would kill a trophy sized wood buffalo at 200m (or charging kodiak at 20m) more dead?
Click to expand...

The deciding factor there would be shot placement IMO, not whether or not you were using a 7mag or a 338.
Cat
 
There are trade-offs to this comparison. Depending on what your going after, focus on the appropriate caliber for the game, shot placement, and bullet construction. Don't worry about BC's, as most ethical hunters know, BC has never killed anything. SD's are important, but should not dictate the killing power of a particular cartridge. Bullet construction and shot placement will rule the day. This comes from the best piece of advice I've ever heard, from a career hunter of big game and a competent gunsmith. Don't overthink it. With the rise in popularity of the mono's, we are seeing how effective these can be used. 7mm-08 with Barnes TTSX on elk comes to mind. SD's and BC's aren't great when compared to "conventional" designs, but they are effective at ethical ranges. Dead is dead.
 
tommy88 said:
Could somebody explain to me how all these factors work together to kill an animal. I've always used energy in ft lbs, but it turns out there's more to this equation. I should also add that I'm not a long range guy, so I'm not too interested in Ballistic Coefficient.

For example: would a 7mm rem mag with a high SD be better or worse then a 338 win mag with a high diameter. I know its a difficult argument because they produce different energy, but you get the point.

270 vs 35 whelen, 243 vs 308 etc......

I know theres more to this; recoil, wind drift, trajectory and whatever else, but is there a relatively simple solution to understanding all of this in terms of "killing performance".
Click to expand...

you could drive a truck into an elephant with 100,000 ft/lbs of energy and do nothing to the elephant because a) there impact velocity is inadequate for the b) sd of the bullet

the easiest way to understand it is look at Kilimanjaro Bell's ~1100 elephants, he killed a great many with 6.5x55 mannlicher and 7x something or other, he was able to figure out that you could get a foot of penetration with 156-160 grain solids (over .3 sd) with about 2200 fps impact velocity...the math in comparing works as solids you can assume the sd doesn't change, the bullet keeps it's shape, if it mushrooms the frontal diameter goes up so the 'sd' or penetration goes down, if it loses weight as it goes the sd drops even further....so here's where it gets interesting...guys figured out that the 700 nitro express even though it could hit elephants with 10,000 ft/lbs energy...the sd on the 3/4" diameter 1000 grain bullets was not high enough and the velocity was too low (2000 fps) to get the necessary penetration and some elephants were only getting knocked out, they'd get back up and start stomping people, it was like hitting them with a hammer instead of a spear...so longer skinnier penetrates deeper (higher sd), shorter fatter is bad for penetration but can smack plenty hard but if you don't have enough of both for game intended you're going to get stomped and energy level has nothing to do with the equation...nothing

we use expanding bullets so as soon as impact starts the sd drops rapidly, so it's really only a guide, and .2 sd bullets are great on deer size game proven over time and seems recognizable that .25 sd bullets and higher are preferred for elk/moose size game, anything over .3 is very high sd indeed and in solid form with moderate impact velocity can penetrate deep enough to get into brain pans of elephants...

energy is basically a useless measure for comparing potential performance between bullets and cartridges, it's a 20th century understanding, the 21st century understanding of terminal ballistics is much improved ;)

there's a thread on rokslide forum about .223's running 77gr tmk's on plenty of elk size game, tons of pics, tons of data, proves this instantly, you'll learn the most there, elk at 400 yards with .223's they don't even blink at that over there as they are very up to speed on 21st century understanding of terminal ballistics, don't try and argue with me here about it until you've read that thread, you'll be a one legged man in an arse kicking contest, just bite your tongue and start learning ;)

I guess a shorter easier way to understand it would be would you prefer to get hit with a hammer or a spear? Which one you think you'd have higher chance of surviving? The spear would have a much higher sd for same impact velocity and it will blow right through you where the hammer is going to leave a mark. Assume dead center of chest, both will likely do you in with head shot but one is guaranteed to do you in on the chest shot and the other you're walking away from it.

so there is a relationship required for game intended regarding sd and impact velocities, if you don't have enough of one or the other...you've chosen poorly for the task at hand and you're going to have failure to achieve your goals, for our game we mostly use .2 to .28 sd bullets impacting as low as 1800 fps and it's enough to get through the vitals of most of our critters on broadside shots, delayed controlled expansion bullets like barnes copper will go deeper as they retain sd (given same impact velocity) but more rapid controlled expansion will do more internal damage over short distances as they disrupt and open up quicker over shorter distances in the animal, many are figuring out that there is a relationship to faster shorter recoveries in bullets that do more work over shorter distances than tough bullets that barely open up until they hit the dirt on the other side...if you have a pressing need to shoot elk up the rump while running away...shoot a magnum with barnes lol, if you like broadside ribcage shots you'll get faster shorter recoveries from adequate sd bullets in rapid controlled expansion construction at moderate velocities than pretty much any other combo out there ;)
 
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stubblejumper said:
The sectional density that really matters, is the sectional density as the bullet passes through the media. If the bullet expands more, the sectional density drops, if the bullet fragments, the sectional density drops. So unless you are using non expanding bullets, comparing the sectional density of unfired bullets, is a flawed comparison.
Click to expand...

unfortunately we don't study the sd reduction rate and finished sd of bullets which I think we should, it sure would cut down on internet traffic lol, we're behind on this as compared to our inflight understanding of ballistics, I also think we could actually study energy but only in energy reduction rate along side sd reduction rates...doesn't matter if you have 2000 ft/lbs if 1200 of them end up in the hillside...but if you can show sd reduction rate over x amount of inches you could show the energy dump per inch as well, it would be a way to standardize terminal ballistics discussions but in ballistics guys are still discussing the wound damage (temp wound cavity, perm wound channel, stretch cavity...whatever...still 20th century views) on the animals themselves and ignoring the answers that could be coming from the finished bullets! I've been going on about this for a few years now, eventually it will get looked at ;)

but you can use the starting sd responsibly to compare, just compare between similar construction/expansion type bullets, ie; rapid controlled expansion or delayed controlled expansion, if they are of same construction/expansion type and they have similar starting sd, they will have similar finished sd and similar sd reduction rate, or similar penetration given same impact velocity, regardless of caliber/weight

so if a guy prefers delayed controlled expansion performance then compare those bullets, many are discovering however that if you have a very high starting sd in more rapid controlled expansion bullets and running moderate impact velocities, you get to peel back a lot more bullet and do more damage over the travel in the animal while still having plenty of sd remain to drive deep enough for the critter intended, think 6.5 creedmoor as the prime example, anything 6.5 have unusually high sd (heavy for cal bullet ranges)

21st century understand of this sure does help one beat their shoulders up a lot less and fine tune far more efficient choices for game intended, it's amazing what you can do with this knowledge, modern bullets and only 30 grains of powder these days ;)
 
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