What kills?

[Redlich]

Splatter,

I would agree in part with your priorities, namely that bullet placement is foremost in importance and that sufficient penetration to the vital area is second. Where I would disagree, however, is taking this to mean that penetration is the only important aspect to consider when choosing a bullet for game such as deer, elk, or moose. If this were true, everybody would be using solid non-expanding bullets all the time. The reality, however, is that in a great many shots there is a great degree of OVER penetration, meaning that the bullet passed through and through. It is never necessary for a bullet to exit an animal, it is only necessary for it to reach the vitals, and that's it. Once it has reached the vitals, the next best thing is to deal the maximum amount of damage it possibly can to the vital organs in order to assure a quick death.

I do not agree with the assumption that just because a bullet reaches the vitals and damages them, it is a good choice for hunting. If you put a pencil hole through the lungs of an animal, it will die... eventually, but rather than dying in 10 seconds or less, it may take minutes, or even longer before it is incapacitated to the point of being unable to move. In that time, the animal is capable of traveling FAR beyond what is desirable or even practical for tracking.

This is why I don't agree that aspects such as bullet construction, crush cavity size and wound channel width are far behind penetration. In my mind, penetration is a minimum requirement that must be met (reaching the vitals, and no more), then maximum tissue damage throughout that depth of penetration is the goal.

The problem of course is that the amount of penetration needed is different depending on shot placement and angle. On a moose or elk you may need 9 inches of penetration from a broadside shot but 24 inches or more with a raking shot. But regardless, my belief is that all the well respected big game bullets are capable of the penetration needed from most if not all angles, at all reasonable hunting ranges. For CXP3 class game that means partitions, bonded cores, monolithic bullets, and in a great many cases even core-lokt/interlock style bullets as well. My $0.02

Red

 

[Dogleg]

Just so long as what you're agreeing with isn't Dogleg's new "Lord of Light" theory!

"Angel of light", actually.

2 Corinthians
"You were to beware of false prophets and false teachers. They will come to you as angels of light"

 

[Boomer]

Have you tried the 350gr TSX Boomer? I bought a box, but haven't loaded them yet. Rumoured to out penetrate even the Rhino 380, and gets velocity up a hair over it too.

The problem as I see it, is that all of the TSXs have a similar depth of hollow point within caliber, regardless of weight. I have stated several times that, "it is as if X bullets were built backwards." Most lead core bullets have a longer lead core making it possible for a heavier bullet to produce a larger frontal area. Whereas differences in weight of various TSX bullets within caliber is determined by the length of the shank, rather than by the length of the expandable nose section; thus there can be no advantage to a heavier bullet over a lighter one. An exception might be where you prefer to have good penetration with a lower impact velocity. For a while I chose heavier TSXs on that basis, but I have shot them enough now to be comfortable with their reliability with high velocity impacts.

So it is not possible for a heavy TSX to create a larger wound diameter than a lighter one, because the expanded frontal area is the same size. Neither is penetration improved, because the greater mass of the heavier bullet has a proportionately lower velocity so the momentum is similar. I would expect a 270 gr TSX impacting 350 fps faster than the 380 to produce similar penetration, as the increase in velocity makes up for the difference in mass.

 

[Brobee]

Anyone care to comment on the penetration qualities of a pointed bullet (that stays pointed) due to a very low impact velocity at extended range.

Can a pointed bullet at very low velocity be directly compared to a certain elephant hunters kills with his 7x57 mauser?

I've also shot alot of gelatin with both traditional-spitzer-ogive-machine-turned-solids and joe-regular FMJ bullets. As Boomer writes, they are inherently unstable and once they loose their gyroscopic (from spinning like a football) stability they begin to tumble. It is pretty much impossible to predict which way they will tumble, but for sure once they do they begin to deflect radically from their original trajectory. This effect is so pronounced that I've had difficulty capturing fired rounds of these types within my gelatin blocks. I disagree with Boomer when he says the bullet will take the path of least resistance; rather I think the deflection angle is opposite to the direction of rotation around which the bullet is tumbling. The deflection force is generated by hydraulic fluid acting on the inclined plane of the now-misaligned bullet shank as it rotates. As you can imagine this is a very dynamic environment and the direction and magnitude of all the forces are changing all the time. The problem is that there is no way to predict which way the bullet will start to tumble.

Why the tumbling and deflection happens is not important though...what is important is that we agree it does happen and that it is a bad thing as it imparts essentially random terminal trajectory through the target media.

Bottom line: Spitzer styled solids will most certaintly deflect as soon as they start to tumble. While the wound geometry as they tumble is pretty impressive, the direction of the deflection is so uncertain as to be pretty much random. The magnitude of the deflection is very significant and can easily thwart otherwise perfect shot placement.

What is nice about the machine turned solids is that they do not tumble and as a result are far less prone to deflection. My testing on big game indicates this is even true when traveling through bone that is hit at strange angles...the flat metplate tends to have no problem cutting a straight path through the full gambit of victim-tissue density.

One last observation I'll add - recall in my first post that I'm of the opinion that what kills quickly is either CNS damage or rapid blood loss from injury to the circulatory system. Circulatory system tissues (things like lungs, major arteries and veins, and to some extent the heart muscles) tend to be pretty elastic. Prior to tumbling, a non-expanding spitzer styled pointed bullet does not so much cut it's way through tissue as it displaces/deflects them. Whether they tear or not as they are accellerated away from their original position and consequently stretched is something of a guessing game, and based on what I've seen dressing out gunshot animals I think this type of tearing happens alot less than folks would have you believe.

Most of the "blood shot" tissue commonly witnessed when dressing your animal is bruising from the tissues being stretched as they are pushed out of the way. While impressive to look at, I don't accept this is as reliable quick-killing mechanism. You have to cut, crush or tear to get cardiovascular tissue to bleed quickly, and the most reliable (and predictable) of these three is both cutting and crushing. The tearing (resulting from stretching) part is a guessing game. I would suggest this is also true of expanding bullets.

As one last footnote - while the solids I'm playing with are certainly inspired by what the folks at GS custom bullets are making, they are not in fact GS custom bullets. Rather I drew them up myself and sourced a kind-of local machine shop to make them for me. Unlike the GS custom bullets they have rebated boat tails, and rather than driving bands (a GS custom bullet feature) they have fouling bands (not unlike a barnes bullet). I'll soon have a complete line of them, starting with 0.277, 0.284, 0.308 and 0.458. Other diameters will soon follow.

Cheers,

Brobee

 

[Brobee]

The problem as I see it, is that all of the TSXs have a similar depth of hollow point within caliber, regardless of weight. I have stated several times that, "it is as if X bullets were built backwards." Most lead core bullets have a longer lead core making it possible for a heavier bullet to produce a larger frontal area. Whereas differences in weight of various TSX bullets within caliber is determined by the length of the shank, rather than by the length of the expandable nose section; thus there can be no advantage to a heavier bullet over a lighter one. An exception might be where you prefer to have good penetration with a lower impact velocity. For a while I chose heavier TSXs on that basis, but I have shot them enough now to be comfortable with their reliability with high velocity impacts.

Boomer, No insult intended - I agree with much of what you've written in this thread however my observations in experiments conflict with your last post.

Three years ago I did a direct comparison between two different weights of Barnes ### in the same caliber: their 130gr .308 at about 2800fps impact velocity and their 150gr .308 at approximately 2600 FPS impact velocity.

.308 130gr @ 2800fps
24.5 inches - total penetration
15 inches - temporary stretch cavity length

.308 150gr @ 2600fps:
27 inches - total penetration
13 inches - temporary stretch cavity length

Sorry for the quality and the lack of consistant scale in the photographs...I was less techically adept in the gelatin-photography department back then.

My observation is that the higher velocity of the lighter bullet (but same expansion charracteristics as the heavier one...same diameter and same geometry) creates a bigger temporary stretch cavity...both wider and longer. The flip-side to this is that you wind up with less overall penetration. Next year if I have enough spare time I'll do all three - a 130gr, a 150gr, and a 165 gr. My prediction based on my experience is that the 165gr, loaded to a proportionally lower velocity, will effect a less impressive temporary stretch cavity but achieve deeper penetration.

Again, not intended at all as a personal attack...just throwing out that my observations are different.

Cheers,

Brobee

 

[Brobee]

So, if I understand you correctly, you've had generally better (more reliable "game killing") performance with these blunt machine-turned solids than with conventional expanding-type bullets?
If so, what do you attribute the success to, if you have formed that opinion.
(If I've distorted the meaning of your post with my quoting and added italics, it was not my intention)

Least amount of potential deflection compared to other bullet types, super deep penetration, and good tissue crushing charracteristics. In general, they cut/crush a nice straight hole that is open on both ends.

Brobee

 

[Redlich]

Addressing Boomer's theory that with TSX bullets, bullet weight is unimportant to penetration because momentum is the same... and expanding on Brobee's disagreement with this idea:

This comes back to the age-old argument of sectional density vs energy on impact. Many people will try to compare the 'killing power' of bullets by measuring the energy they have on impact in foot-pounds, I'm sure most of us have seen this data, it's basically a function of the weight of the bullet and its velocity: aka momentum.

Sectional density, on the other hand, relates to how wide an area this force is exerted across at the front of the bullet. Assuming you're right Boomer that the different weight of TSX bullets all expand to the same diameter on impact (I wouldn't know either way), this still means that although a light fast bullet and a slow heavy bullet have the same energy on impact in momentum, the slow heavy bullet is pushing relatively more force and weight onto the same area as the lighter one, thus transferring its energy more gradually but deeply. You can see this in Brobee's gelatin where the lower sectional density expended more energy making a large stretch cavity while the higher SD "slow heavy" bullet spent its energy drilling a deeper hole with more weight behind the same frontal area.

I'd never actually heard that heavier bullets in the same caliber are supposed to be designed to expand to a wider area, I was under the impression that expansion was similar for all bullet designs in caliber regardless of weight. I haven't measured, but I've read that it's usually twice the original diameter, so for a .30 cal bullet it should mushroom to about 0.6 inches across regardless of if it's a 150 grain or 200 grain, assuming they both mushroom fully. Am I wrong in this? Because if heavier bullets are in fact designed to mushroom wider than light bullets of the same caliber then that can potentially change things in bullet choice.

Directed at Brobee, what game are you designing your solid bullets for? I think most people would agree that in most cases it's appropriate to choose different bullets for different game. Are you designing yours with the intent of use on dangerous game specifically, or do you think it's a good choice on everything including whitetails?

Red

 

[Neo]

"Angel of light", actually.

2 Corinthians
"You were to beware of false prophets and false teachers. They will come to you as angels of light"

Funny, I always had you pegged as an Ezekiel 25:17 man... The Samuel Jackson/Pulp Fiction version, of course. Kinda always imagined you rattling that off just before squeezing the trigger.

 

[Boomer]

The following pic shows a trio of recovered bullets: a 270 gr XLC, a 300 gr X, and a 380 gr Rhino, all .375 caliber.

You will note that although the wings broke off both X bullets, the expanded nose section is about as big as it would have been with the wings in tact, at .72." Conversely, the 380 gr Rhino expanded to .92." Despite the vast difference in weight and impact velocity, all 3 bullets penetrated equally each stopping at 32" of my test material. The wound volume was very similar between the two X bullets, but the 380 Rhino's was larger by a factor of 3X.

If we were to consider a 130 gr lead core bullet and a 220 gr lead core bullet, both in .30 caliber, it would not be unreasonable to assume the 220 would upset to a larger diameter, due to the longer core, provided both expanded bullets remained intact but expanded to their full potential.

Brobee, no offense taken, and any observations, especially ones that do not match my own are appreciated. I may have over looked something or come to an incorrect conclusion through a ballistic fluke. Let me mull around your .308 test results for a bit, and I'll get back to you. A 150 gr bullet in the .308 should be pushing about 2950 at full steam and the 130 about 3150, for a difference of 200 fps. Although you didn't shoot these at full speed, the 200 fps difference in velocity is correct. I've got some 130s and some 180s, so I'll have to conduct a test I suppose. Wait, I think I see something in your pic. Did you keep that 130 gr bullet? I'd be interested in knowing if there is any shank extending below the expanded frontal area. If not, the bullet may have gone into a yaw, not having a linear axis to rotate around. If the bullet yawed after expansion, that would limit penetration, and would also account for a larger wound diameter.

With respect to bullets killing game, for many years I was convinced that Taylor's Knockout Value was the best index of a bullet's killing power. I would always point out that the kinetic energy of the factory 405 gr .45/70 was the same as that of a 55 gr .22-250, yet one only had to see the comparison on game to understand the difference. When I came north, everyone seemed fixated on killing everything in sight with .22-250s firing factory ammo, and my belief in TKO ended. I played around with SD for a while thinking the answer may lay there, but of course SD goes south as soon as a bullet expands, so that didn't do it. Well, what about kinetic energy multiplied by SD? In the end I gave up on the whole idea of being able to mathematically predict an animal's demise through a simple formula. If there is one, it won't be simple. I like heavy bullets and powerful rifles, and my choices reflect that, but when I start to think that's what it takes along come some native guy, with a sleigh full of moose meat, and a .22 centerfire slung across his back. Maybe there's a message in that . . . naw, it was just dumb luck . . . again!

 

[Redlich]

Just out of curiosity Boomer, what was the final weight of the three bullets in the picture? You mentioned that for the first two the wings broke off, so there must have been some weight loss unless they came off after the bullet came to a halt. Similarly, I'm curious how much the Rhino retained.

Red

 

[Brobee]

Brobee, no offense taken, and any observations, especially ones that do not match my own are appreciated. I may have over looked something or come to an incorrect conclusion through a ballistic fluke. Let me mull around your .308 test results for a bit, and I'll get back to you. A 150 gr bullet in the .308 should be pushing about 2950 at full steam and the 130 about 3150, for a difference of 200 fps. Although you didn't shoot these at full speed, the 200 fps difference in velocity is correct. I've got some 130s and some 180s, so I'll have to conduct a test I suppose. Wait, I think I see something in your pic. Did you keep that 130 gr bullet? I'd be interested in knowing if there is any shank extending below the expanded frontal area. If not, the bullet may have gone into a yaw, not having a linear axis to rotate around. If the bullet yawed after expansion, that would limit penetration, and would also account for a larger wound diameter.

I handload all my test projectiles, and purposely target velocities that are less than what they would be when using standard loading practices. The reason for this is that I am more interested in a realistic/representative impact velocity rather than what's happening at the muzzle. I've tried to target velocities to simulate hitting after incurring between 100 to 200 yards worth of atmospheric drag induced velocity loss.

Yes I still have the recovered 130gr .308 barnes slug. As an aside I also have a couple that were recovered under the skin on the backside of a couple mule deer I shot with them; interestingly enough it is difficult to tell them apart from the gelatin shot slug. As a second aside all of the .308 barnes bullets (across the entire weight range I've played with...the 130gr, the 150gr and the 165gr) I've recovered from both game and gelatin exhibit approximately the same degree (ie: diameter) of expansion. They all have the same cross sectional area after expansion.

Anyway, the gelatin shot barnes ### 130gr .308 slug exhibits no evidence of tumbling or yaw...evidence to support this is the continuous corkscrew-like character of the temporary stretch cavity caused by the 4 petals as they rotate through the media...it simply penetrated less despite it's higher initial velocity. While I am not sufficiently educated to understand the fluid dynamics involved, I suspect this is because it's higher initial velocity effects greater work earlier in it's terminal trajectory.

Cheers,

Brobee

 

[Brobee]

Directed at Brobee, what game are you designing your solid bullets for? I think most people would agree that in most cases it's appropriate to choose different bullets for different game. Are you designing yours with the intent of use on dangerous game specifically, or do you think it's a good choice on everything including whitetails?
Red

While I think the flat metplat machine turned solids are very appropriate for use on larger, more dangerous animals, my personal opinion is that they are also well suited for deer sized game for a couple of reasons. The first one is that their deep penetration allows for a greater range shot opportunities with respect to aspect or angle.

The second is the confidence I get knowing there will be little deflection.

And lastly, as a hunter who hunts for meat what's most important to me is the more evenly distributed and focused trauma throughout the wound channel. What I mean by that is I can punch the front side shoulder, the back side shoulder, or even both shoulders and not have to sacrifice a large amount of blood-shot meat. As I've written previously, while visually impressive, I believe that tearing up the skeletal muscles is not a trauma mechanism that kills quickly.

There is a drawback to this bullet design though, and it comes in the trajectory department. These bullets are definitely not as aerodynamic as their spitzer ogived kin. As such they have very real practical range limitations. I'm going to do a science project on this (velocity dropoff and resulting in-flight bullet trajectory) next summer once my range is a bit more clear of snow; in the interim these past few years of hunting with them I've limited myself to shots under 200 yards.

Cheers,

Brobee

 

[Redlich]

Brobee,

I'm not sure if you're looking for more real-world data than this, but I've seen ballistics calculators available that can give very meaningful and accurate ballistic data for any load or bullet design/shape/weight if you provide the bullet weight and the actual muzzle velocity and actual velocity at 100m as measured by a chrono. The programs can do the rest, and are even accurate enough for competitive 1000 yard target shooters to use the predictions for drop data using their custom handloads.

Of course, nobody here will mind if you do the grunt work of actual measurement and give us the condensed results

Red

 

[tactical lever]

A few thoughts: Boomer, get a real grouse gun; at least .400 cal. I guess I shouldn't talk, I took a couple with a mere 30-30 and 6.5x55 this year.

Speaking of tumbling, I don't think this is an accurate description. I believe it's swaps ends once, although if it's sufficiently rounded off enough, maybe more. I can't disprove this.

I think it's fairly important to have exit wounds, although if the angle and size of animal is near impossible to achieve this on, they by all means, dump it all in the chest cavity. Exit wounds bleed, allowing better blood loss than the small entrance wound. Having unbroken skin on the other side is like having a bandage in place.

I think the natives with a truckload of meat and a .22 center fire are getting in a lot more practice than us although maybe you're not seeing the runaways. I've heard some bad stories about that. I killed a deer with a hornet, and the same one did in a black bear by my Dad's hands, but the small bullet was far from ideal; however the shot that Dad took was better suited to the bullet construction (neck).

 

[Boomer]

Just out of curiosity Boomer, what was the final weight of the three bullets in the picture? You mentioned that for the first two the wings broke off, so there must have been some weight loss unless they came off after the bullet came to a halt. Similarly, I'm curious how much the Rhino retained.

Red

I don't remember the retained weight; I was afraid someone would ask me. I'll see if I can find the bullets and reweigh them. I'm fairly confident that the retained weight was 70% for the Xs and 90% for the Rhino.

Edited to add . . .
380 gr Rhino - recovered weight 363.7 grs - 95.7%
300 gr X - recovered weight 212.2 grs - 70.7%
270 gr X - recovered weight 194.2 grs - 71.9%

 

[Boomer]

I handload all my test projectiles, and purposely target velocities that are less than what they would be when using standard loading practices. The reason for this is that I am more interested in a realistic/representative impact velocity rather than what's happening at the muzzle. I've tried to target velocities to simulate hitting after incurring between 100 to 200 yards worth of atmospheric drag induced velocity loss.

Yes I still have the recovered 130gr .308 barnes slug. As an aside I also have a couple that were recovered under the skin on the backside of a couple mule deer I shot with them; interestingly enough it is difficult to tell them apart from the gelatin shot slug. As a second aside all of the .308 barnes bullets (across the entire weight range I've played with...the 130gr, the 150gr and the 165gr) I've recovered from both game and gelatin exhibit approximately the same degree (ie: diameter) of expansion. They all have the same cross sectional area after expansion.

Anyway, the gelatin shot barnes ### 130gr .308 slug exhibits no evidence of tumbling or yaw...evidence to support this is the continuous corkscrew-like character of the temporary stretch cavity caused by the 4 petals as they rotate through the media...it simply penetrated less despite it's higher initial velocity. While I am not sufficiently educated to understand the fluid dynamics involved, I suspect this is because it's higher initial velocity effects greater work earlier in it's terminal trajectory.

Cheers,

Brobee

You didn't say whether or not there was any shank exposed below the expanded portion of the bullet. A slight momentary yaw would not necessarily result in a loss of the cork screw bullet tract, but it could account for what appears to be a greater amount of energy being released upon the target material, resulting in a more rapid decay of velocity, thereby resulting in slightly less penetration. When the bullet expands, it's center of gravity moves forward very rapidly, and if the high rate of rotation suddenly has no linear axis to rotate around, a momentary instability is possible. As I've said, my experience suggests that when momentum and shape are equal, so will be penetration, and the only thing that can account for the difference in penetration is a difference in shape, as momentum is very similar.

As a real world comparison to my test with the .375/380 gr Rhino, I can offer the following. When I got my African buffalo, we recovered a .510"/580 gr X bullet which expanded to .92" the same expanded diameter as my test 380 gr Rhino. The muzzle velocity from the .500 was about 2150 fps, (chronographed at the time of loading) which compares to 2300 from my .375 Ultra carbine. At 50 yards, the 580 would still be chugging along at 2100, so we could call it a 200 fps velocity difference. The 380 gr bullet in my test penetrated 32", the 580 gr bullet in the buffalo penetrated about 32" as close as we could measure, go figure.

Here's a pic of the recovered .510/580 X with the same .375/270 XLC from my earlier test for comparison.

With respect to bullet testing for realistic conditions, my testing is for just off the muzzle because defensive shooting rather than hunting is my greatest concern and interest. When I conducted that bullet test in 2005 it was in anticipation of confronting an African buffalo, but also to see which bullet had the most potential as a bear defense bullet. My criteria was that I wanted a bullet that simply will not fail under any circumstances, and the 380 gr Rhino won in spades. The newer TSX design has tougher petals, so perhaps a repeat of the test is in order, along with some .375/350 gr Woodleighs, .458/550 Woodleighs, .308/240 Woodleighs, and maybe a few Swift A Frames which have received some pretty good press. So many bullets, so little time.

 

[Brobee]

Boomer - to address your question on shank characteristics see the following for photograph comparing some of my recovered .30 Barnes ### bullets:

http://www.eclecticworks.ca/pics/misc/bullets/barnes_308_###_comparison.jpg

After seeing the closeup photograph it appears to me that the petals on the lighter slug are actually longer than those of the heavier (and slower impacting) slugs. The final expanded diameters of the recovered slugs are all approximately the same diameter, however it would be interesting to know if there is a point in time mid-way through their terminal travel where they are much wider, possibly in proportion to the length of an expanded petal. Unfortunately I don't have any high speed photography gear so I can't set up an experiment to tell. It would be difficult to set up too as the best angle would be right inline with the axis of penetration.

Redlich - Using a couple chronographs and some of those ballistics calculators you mention is definitely part of my plan. This should produce some good ballistic coefficients for those inclined to crunch numbers. There is 2 feet of snow out at my range right now though and I still have to purchase the second chronograph. Also, two kids, the wife, and my full time job compete for time, so I'm thinking I'll make it a summer project. I also have plans to set up a large target (48 inches tall) and do a visual demonstration of drop, zeroing at 100 and then backing up to 200, 300, and maybe even 400, shooting the same target which should nicely illustrate the trajectory with a standard .308.

Brobee

 

[Boomer]

There is certainly enough shank exposed on the 130 to maintain stability, so that shoots that theory down. Nice pics by the way.

 

[Redlich]

Brobee,

Snow on the ground and other time constraints are hard to argue with but I don't believe you need a second chrono, I think that's overkill. Simply getting an average muzzle velocity from the same load out of the same rifle by averaging 5 or 10 shots at the appropriate distance from muzzle, then moving the same chrono to 100m to get a 5 or 10 shot average 100m velocity from that load and rifle should give you as good of results as you need.

Red

 

[Redlich]

Boomer,

You mentioned before that sectional density goes out the window on impact because of expansion, I don't entirely agree. It does change, as the frontal area of the bullet changes, but comparisons can still be made between bullets that expand in similar ways. For example, if two TSX bullets both expand to the same diameter and they both retain 100% of their weight, but one is 50 grains heavier than the other, then the heavier one will still have a greater SD than the lighter one even after expansion.

Your example of the three bullets, a 270gr TSX, 300gr TSX, and 380gr Rhino all in 375 cal that you mentioned before is an interesting one. Prior to expansion they had the follow SD values:

270gr = 0.274
300gr = 0.305
380gr = 0.386

This is a fairly significant difference in sectional density between the highest and lowest, representing a difference of 0.112 which is 29% of the total SD of the greater bullet. You seemed perplexed at your penetration figures, however, when you observed that they all penetrated 'about' the same amount. It's interesting to look at the sectional density of these bullets after expansion and after their weight loss during impact:

270gr, 194.2gr remaining at a diameter of 0.72 = SD: 0.05352
300gr, 212.2gr remaining at a diameter of 0.72 = SD: 0.05848
380gr, 363.7gr remaining at a diameter of 0.92 = SD: 0.06139

The total difference in SD between the greatest and smallest of these values is 0.00787, which is 12.8% of the total value of the heavier bullet. For reference, the difference in SD between these 3 bullets after impact is roughly the same as the difference (pre-impact) between a .308 cal bullet that is 150 grains, and one that is 155 grains.

So you can see that during expansion the sectional density difference here shrunk from 29% to just 12.8%, which to me is an important thing to point out. Although the Rhino had the clear advantage at first, it also expanded much wider than the other two bullets, resulting in all 3 drilling a reasonably similar depth hole. Rough calculations based on a single firing are hardly scientific, I'm just suggesting that the penetrations were similar because the effective sectional densities were similar given the difference in expansion width.

However, as you said the Rhino carved a much WIDER channel than the other two, because it not only opened wider but retained enough of its weight to maintain similar density to the TSX bullets at the same time. The TSX bullets would no doubt have penetrated measurably deeper had they retained close to 100% of their weight as (I believe) they were designed to.

My conversion of sectional densities into post-expansion forms isn't meant to imply that you can derive a formula out of any of this, since the shape, velocity, frontal area, and energy of the bullet would be constantly and dramatically changing throughout the entire impact event. Some bullets may mushroom more slowly, thus maintaining a higher SD longer during penetration, some may open wider than others, some may even open exceptionally wide at one point and then narrow again... who knows? The point is that I think SD is still important during and after expansion in determining penetration.

In a way, how a bullet expends its energy while moving through the air has comparisons to how it moves through a solid medium such as an animal. If you want to know which bullet will fly the farthest before reaching a zero velocity through air, fire two bullets with the same muzzle energy and watch the one with the higher ballistic coefficient, because it'll be the last to stop. Even if the higher BC bullet had a slower starting velocity, as long as the muzzle energy is the same, the higher BC bullet wins every time. BC as I'm sure you know is derived from the sectional density and the bullets shape.

I believe it's the same thing with penetration into an animal. If you fire two bullets with the same muzzle energy, the one that MAINTAINS the highest SD throughout expansion will penetrate the farthest, regardless of initial velocity... all things being equal, and within reason! And of course we're measuring the SD based on the frontal area after mushrooming. If one bullet opens wider than another, or one bullet retains more weight than another, that all comes into effect in determining the 'penetration coefficient', if you want to call it that.

That's why solid bullets do what they do!

I'd go a step further with my generalizations by saying this as well: the bullet that loses the most energy in the first stage immediately after impact will create the biggest temporary cavity. After all, that's where the energy goes that the bullet lost... into that expanded cavity. In general one bullet will lose energy on impact more quickly than another because it has a LOWER sectional density (either pre or post mushroom doesn't matter, it is lower in both cases). In other words, it has a bigger frontal area to slow it down, and the force exerted on the medium while being slowed at a faster rate than a dense bullet makes a bigger cavity.

This is why the example that Brobee gave of the two 308 cal bullets make sense to me. If they have the same muzzle energy, the less dense bullet dumps its energy faster making a bigger cavity because it is distributing less force per square inch across its frontal area. The more dense bullet slows down less dramatically while traveling through the medium, thus the smaller cavity on entry because it spent less energy there, instead retaining that energy to drill a deeper hole.

To go back to the travel through air vs travel through a solid analogy, you'll see the same thing with a lighter but faster bullet compared to a slower heavier bullet in the same caliber in flight. The faster bullet slows down more dramatically in the first few hundred meters of flight than the slower bullet does, "dumping" that energy into the air more quickly.

So to sum up: ASSUMING the same calibre, the same muzzle energy, and that the bullets will expand to similar final diameters during impact...
-The higher SD bullet will impact at a slower velocity and penetrate deeper
-The lower SD bullet will impact at a higher velocity and create a more devastating amount of tissue damage immediately after expansion (such as in the first 12 inches) but not penetrate as deeply.

Brobee,

Your concept of a flat nose bullet being deflected less during impact has connections to the "ideal brush gun" bullet choices of the past. It's been shown that the larger the caliber, the heavier the bullet, and the flatter the nose, the less the bullet is deflected by things such as grass, twigs, and leaves during flight. With a very flat nose such as those in traditional lever action guns, the twigs will often be severed by the bullet instead of being pushed aside by a spitzer (while also deflecting the spitzer more than the flat nose). I see a strong connection between this and your ideas about displacing vs crushing tissue during impact.

As a final note, I respectfully disagree with the idea that an exit wound is important for killing game swiftly. Even if it does let more light in
There is way more than enough space inside the chest cavity for blood to flow and cause death. If you could somehow rupture an animals lungs with a high powered ghetto blaster pounding "In the Air Tonight" by Phil Collins, it would die just as quickly whether there was one hole in the chest, two holes, or no holes. There is no difference between bleeding externally and bleeding internally, except that it looks more impressive when it's coming out. In both cases it's still blood loss though. If you were trying to collapse an animals lungs by letting air into the chest that'd be another thing, but that's not even really a factor in death compared to the massive trauma/blood loss of perforated lungs.

The perfect bullet would in all cases stay perfectly solid without deforming until it had penetrated right to the lungs (or brain, if that's the target) and then as soon as it reached there, shatter into pieces going every which way, smashing the lungs/brain with all the remainder of its energy and mass with no further penetration at all. Unfortunately we never know exactly how deep the bullet will need to go to get there, or what bones/muscle it might need to drill through on its way! THAT'S why penetration gets so much hype, but after the bullet has passed through the vitals, it's a waste of energy.

Man... sorry... that was long. If anybody actually read all the way to the end, Thank you! Just my thoughts on what's been discussed in this thread so far.

Red