Understanding The Phenomenon Of Jacket-Core Separation

My only bullet failure was with 2 of the Barnes solid coppers that did not open up at all. Pencil size holes in and out. Animals ran about 200-250 yards before expiring. Spoiled me on them. Well that and the copper fouling.
f you lost the animal and couldn’t examine the bullet, how do you determine it was bullet failure by the core losing its jacket?
in this case, i did not lose the animal and was able to see what happened to the bullet. the fragmented bullet on such a small animal told me (assuming the bullet would repeat its performance) that on a moose, the bullet would have fragmented too much to penetrate a moose properly (or caribou or large bear). i would prefer the bullet held together and got more penetration, but the story that bullet told me was it would not be a great choice for larger game. that is pretty much what i have up here in AK
Some bullets, and there are still some on the market, were designed to fragment and the weight loss was inevitable. It was a lot of advertising around them in the past. The famous cartridge 8x68S was initially marketed with such a bullet.

H-Mantel Geschoss RWS

Another bullet that loses much of its weight, but still surprises with its effectiveness.

In Burkina Faso, a hunter shot a buffalo with the cartridge 9,3x74R and the 9,3mm 238gr/15,4g GPA bullet. I warned him beforehand in the camp that this bullet was a bit marginal for buffalo hunting. Nevertheless, everything went without any major problems. The buffalo walk a few hundred yards before it dropped dead.

Summarized, separation of core and jacket with significant weight loss of the bullet does not always have to be viewed negatively. In theory it seems detrimental, but in practice it is often more effective than would be expected. No matter how, the pathway of a bullet in the body of a game, whether an old or a modern bullet, can never be predicted in advance with absolute certainty.

In all cases very important is the shot placement and the use of enough gun, if possible a little bit more.
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I have not yet read the whole thread but to answer one of the OP's questions about bullet failure. If the core separates and the animal is killed relatively quickly I do not consider that to be bullet failure. If there is a long tracking job and the bullet has been placed right then yes I would consider that a bullet failure.
Just my 2 cents worth.
Alright, Gents. A discussion for you all.

It goes without saying that those of us who've hunted with cup & core bullets... have all experienced jacket-core separation at least once or twice (if not more) in our hunting lives. Especially older hunters like me who began our adventures at a time when bonded or monolithic bullets were completely unheard of.

My question is: Do you always consider jacket-core separation to be an example of bullet failure ?

Take myself for example:
In 1974, on my life's first Safari to Africa (Kenya)... I lost a huge male lion (over bait) after my bullet (a 300Gr Winchester Silver Tip fired from a .375 Holland & Holland Magnum BRNO ZKK602) had failed to reach the vital organs. After my white hunter, Mr. Cheffings successfully spoored & finished off the lion with his .458 Winchester Magnum B.S.A Majestic... a postmortem revealed that my Winchester Silver Tip had experienced jacket-core separation & failed to penetrate the six inches of hardened feline frontal chest muscle.

In 1989, I attempted to make a double lung shot on a man eating Royal Bengal tiger with a Winchester Super X 175Gr cup & core point fired from my 7x57mm Mauser Churchill Gun Makers Model Deluxe. The animal succumbed to the gunshot wound on the following day. Postmortem revealed that my bullet had broken through the scapula & only penetrated one lung before experiencing jacket-core separation. The man eater died but one can hardly claim this to be a clean dispatch by any stretch of imagination.

Now, on the flip side of things... I've frequently shot (among other game animals) wildebeest & zebra with the aforementioned Winchester Super X soft points for the 7x57mm Mauser. And also (in recent years) the Prvi Partizan 173Gr cup & core soft point. When used on wildebeest & zebra, both the Winchester & the Prvi Partizan 7x57mm Mauser bullets are guaranteed to experience jacket-core separation (especially when hitting hard bone). But the wildebeests and zebras all gave out within mere seconds of getting shot.

So I'm basically asking: Have any of you experienced jacket-core separation with a bullet during the hunt ? And if so, then what was the ammunition & what was the game animal ? And did you successfully drop the animal or not ?

Warmest Regards,
I also have experienced core separation with cup and core projectiles.
As long as the animal is dispatched quickly and cleanly I do not regard it as bullet failure.
On the other hand it doesn't matter if I'm using old style cupe and core, premium bonded or the mono metal projectile if the target animal is not dispatched cleanly and I know I have done the job properly then I regard that bullet as a failure and look at why. May be seperation, over expansion and failure to penetrate or minimum to zero expansion so no transfer of energy.
Despite all the modern advances I still do 95% of hunting with cup and core as mostly they just plain work if used within their paremeters.
Just my opinion.
It is an interesting question. On other forums with more long range hunters I've seen lots of pictures of ELDX bullets and similar bullets that came apart in Elk but still killed well. A friend shot an ELDX through a mid sized grizzly with good results. Another friend shot a 308 150 gr SST through a moose. I don't think a perfect mushroom is as important as a quick kill. I'm going to try some softer bullets this year and see how things go. I'd be tickled if a softer 308 bullet gave performance similar to my .358 for example.
@Alaska Luke
My son uses150gn SSTs in his 08 with devastating results. The front expands quickly but the shank seems to hold together well. Only ever recovered one
A 308 will be very hard pressed to give performance similar to a 358
I do believe that there is not a lot of difference between smallbores. A 270 hits a lot like a 6.5 PRC and a 280 AI but they’re not the same. A 165 gr 308 is not that much different than a 180 gr 30-06 (same bullet, impact distance, animal etc). But a 30 cal and a medium bore is a big difference. Enough of a difference in bullet weight, construction, velocity, or caliber and they behave very differently or at least have the ability to kill vastly larger and/or tougher game as quickly but maybe not quicker.

As I said above, I have come to believe in heavy for caliber, modest velocity impacts with appropriate bullet weights and cartridges. I’m blessed to have more than one rifle, so I can use an appropriate one for a given class of animal. Or, with my R8, the appropriate barrel. I’ve also come to believe in conventional wisdom for cartridge selection vis a vis game size. I.e. 6.5 CM can kill an elk, but a 300 magnum (or similar) is a better choice. My plan is to take a 375 and 300 magnum barrel to Namibia for plains game (sound familiar??). I was planning to take a 6.5 PRC for my second barrel, but it’s not legal for larger plains game. I’m hunting kudu, gemsbok, black wildebeest, eland, and springbok and a 300 and 375 are enough for any of them. If a scope fails, I’ll switch barrels. If open terrain - 300 magnum with a higher magnification scope. If closed terrain or bigger animal being targeted - 375. Barnes tsx and LRX bullets. I’d happily take A-frames, but these are more available. Should be enough for just about anything.

Pushed to the extreme - ultra heavy, slow trajectory suffers - light, ultrafast requires risks bullet blowup or erratic penetration (direction of it depth).

I think (at least when I started) this is at least tangentially related to the thread. If it’s not, feel free to give me a thumbs down lol!
@Alaska Luke
My son uses150gn SSTs in his 08 with devastating results. The front expands quickly but the shank seems to hold together well. Only ever recovered one
A 308 will be very hard pressed to give performance similar to a 358
I have had some pretty impressive kills with my 358 and I think it's superior to my 308 with similar bullets like a 225 Nosler Partition vs a 200 grain NP. On the other hand I've seen softer 308 bullets kill very fast. And they aren't failing to penetrate. So how will a softer medium weight 308 compare? We'll have to see.
I think the real question is
1. How much penatration do we need? Once we achieve that more is a waist of time.
2. Once we have the penetration we want to make the hole wider not longer.
I think that there is another facet to this discussion that has not been discussed much, and that is, that while I agree with what most posters have mentioned, there are some c&c bullets, specifically, certain product lines in certain calibers that are gems and others that are stinkers. This is something that can only be learned through experience, either your own or through books or websites.

A couple of examples.

Nosler's 257 cal 115 ballistic tip is an awesome bullet. Over the years, the only times that I've seen one stopped were when my son's buddy shot a cow elk through a shoulder at 60 yards, and a 400 pound black bear that my brother-in-law shot with my 25-06 at about 125 yards. Every other time I've seen them shot into something, either near or far, they've left awesome exit wounds. I believe this particular bullet is almost perfect and greatly outperforms most of the rest of the Ballistic Tip line. I say this about 25-06 velocities because I have no idea how it would perform out of a speed demon like a 257 Weatherby.

Another example

For many years, when it was still legal, my Dad was shooting elk with his 50 cal Knight muzzleloader using 300 gr bonded sabots. He had great luck with them. One year he couldn't find any bonded 300 sabots so he purchased the non-bonded variety. I think they were Hornadys) Thinking that this 45 cal, tipped 300 gr bullet at 2300 to 2400 fps would most likely penetrate good enough to get the job done. He tracked down a little 4 or 5 point bull and at about 30 or 40 yards shot it behind the shoulder. The bull stood there. So he reloaded and put another one behind the shoulder. The bull stood there. He reloaded again and the bull was still standing there. Dad said that at this point he was thinking that maybe the bull was only appearing to be still standing, maybe he was tipped over against some brush (North Idaho is usually very thick) so he circled down the hill to get behind the bull to see if, in fact, the bull was still on his feet. When he got behind the bull to where he could see it, the bull turned his head and looked back over his rump at my Dad and Dad took him down with a shot to the neck. When he opened the bull up, he found 2 grapefruit sized balls of hair inside the chest cavity! Apparently, those non-bonded sabots absolutely detonated on the hair of the bull and created huge surface wounds with very very little penetration.

Sometimes you just have to be there to see what happens. For the most part, the performance of c&c bullets launched at whatever speeds can be roughly predicted by the the game animal, shot placement, bullet type, and impact velocity, but there are exceptions that defy expectations. Gems and stinkers.

Most bonded, partition-style and mono bullets, in my experience provide more predictable results. However, c&c bullets still have their place, especially at long range.
I shot a hartebeest with a Hornady light magnum 30'06. (a probable mistake to trade extra velocity for those Hornady bullets they came with?) Killed it, but the lead core was found as a little tear drop and the cup turned the wrong way. Later in the same hunt with the same bullet, my only gemsbok ran off from a shot tight behind the shoulder from a literal bench rest position. Two days of bushman tracking still did not recover it! You can imagine my thoughts about that bullet. Both shots were taken at about 100 meters. I WANTED to shoot the gemsbok with a 220 gr partition, but the outfitter forbade it, saying he had seen too many fail....
The cup itself on all cup separations I have seen have been found facing the opposite direction fired. Are they dumping the core while turning--who knows??
I have seen more separations from boat tail bullets than flat base.
Long distance=slower impact velocity=fewer cup separations.
Long heavy bullets have held together and kept straight line penetration, even if torn up by hitting shoulder bones.
Monometal bullets need speed, so may be at risk at extreme range of unsufficient mushrooming, though I have not had one fail, or even break off petals.
Those are my two pesos...
Crossone sounds like you are describing a true failure to me. That's what I'd be interested in. How bad does a bullet have to be to really not work on an otherwise solid hit.
Crossone sounds like you are describing a true failure to me. That's what I'd be interested in. How bad does a bullet have to be to really not work on an otherwise solid hit.
Those muzzleloader sabots were definitely not up to the job. I believe the only other time I've seen a bullet completely fail was my buddy shooting a mule deer buck with a 180 Sierra gameking out of a 300 Winchester. My buddy had a full 26 inches of barrel and he was a velocity freak so he was getting 3300 fps out of them but at 350 yards the bullet completely disintegrated. The buck went down and rolled down the hill out of sight. When we got closer, the buck was up so he shot again, too high and too far back, right above the guts and into the backstrap. This was at about 80 yards. Again the buck went down but he needed a finisher. When we cut it up, the first bullet had only penetrated few inches into the brisket in front of the shoulder. The second shot was the same. Only a few inches of backstrap were torn up from an almost perfect broadside shot. The spine hadn't even been hit. The bullet didn't penetrate that far. I know people like these bullets so my guess they're better at .308/30-06 velocities.
I’ve had a few instances of bullets coming apart. Fortunately, all of the animals died fairly quickly.
The first was a mule deer at ~60 yds, with a 250gr Sierra in a .338 Win mag. The buck walked about 40 yds and stopped. Stood for a second and collapsed. I expected the bulllet to make full penetration, but actually totally broke apart, with only small pieces of the core making it to the opposite ribs.
I took a mule deer at ~300 yds, using a 190gr Hornady in a .300 Wby. Perfect performance. Broke the shoulder and exited behind the far shoulder. Upon returning home from that hunt, a friend asked me to go hunt exotics with him. I just grabbed the .300. A ram came out of a valley and I shot it just behind the shoulder at 20 yds. It instantly dropped. As I started to approach it it looked a little strange. Ribs were sticking up and the scapula exposed. That was the entrance. No exit. Only found bits and pieces of jacket and lead in the lungs.
I used a 220gr Sierra Silhouette bullet from a .44 mag revolver on an javelina at 30 yds. Shot thru the shoulder. No exit. Hunks of jacket and core thru the wound channel and a few made it to the far ribs..
I think that velocity at point of impact also plays a big part in bullet performance. Too fast and it can disintegrate on impact , too slow and it will fail to expand and /or penetrate. And as mentioned, different calibres of the same projectiles perform differently, I use 196 gn S&B SPCE in my 8x68 and they seem to work fine, but another poster had issues with them in another size, my 17 fireball loves 17gn noslers at 4000fps ,but another guy over here had them disintegrate out of his 17-06 ( and yes that is a 30-06 necked down, massive barrel burner) The only projectile failures I had was with z-max projectiles on a goat (first shot blew up on the scapula, second took out the throat and the third took out a bone on the vertebrae, (it kept moving, had to chase it down on foot and cut its throat to put it out of its misery) and that was due to the completely wrong projectile choice by me, it was what was in the gun at the time whilst culling roos'. I’ve heard of people having straight pass throughs on deer as they were too close for the speed they were driving the projectiles
I have experienced core jacket separation on several occasions but have been lucky in never losing an animal. In my experience there are two factors that contribute to this phenomenom. The most common being driving a cup and core bullet too fast beyond its design envelop. The second as mentioned by others is hitting heavy bone. I have altered my reloading for cup and core bullets by using heavy for caliber bullets and when available using round nose bullets. It sounds counterintuitive that a Spitzer bullet would separate more often than a round nose but that has been my experience. As far as partitions losing their front half I don't really consider that bullet failure as that is exactly what they were designed to do and I have never had a partition Fail to kill and do it quickly. Just one old hunters experience.
@NS 9x56
The old round nose seems to have a much more dramatic effects in game. Yes you may have to shorten your shots but in reality how often is game shit. Past 250 yards. I can honestly say 90% of the game shoot would be less than 200.. This big 250gn 35 cal round nose really hammer bigger critters.
Yes. It seems to be a common occurrence with 165 Nosler Partitions fired from my 30-06 Springfield. The front of the bullet ahead of the partition comes apart while the rest continues on the original trajectory. They typically look like this.
View attachment 598674
One slug recovered from blue wildebeest and one from gemsbuck. Both shot through the shoulder and bullets didn't quite exit from hide on opposite side.

But not always. This slug recovered last fall from a frontal boiler room shot on my third gemsbuck did not come apart.

Difference may be that it was Federal factory load and the other two were my reloads. All animals shot fairly close, fifteen to one hundred yards.
Yeah typical crap performance from NP.
I dont remember I had a bullet failure such as jacket core separation, or similar.
However, I believe that there is a hidden problem in C&C bullets, when hitting a hard target, or when on magnum velocities.
But I witnessed this once, when hunting with a friend, and it was his bullet on roe deer.

So, since I follow my theory on hard targets or high velocities, and I often use some type of C&C bullets, here is my formula.
For roe deer (thin skinned, smallish animal, of about 60 pounds), I use 30-06, and 180 grains nosler ballistic tip. Never failed. (velocity cca 800 m/s)

For boar (on occasion hard and tough target, resilient to gunshots) I use 9.3x62 round nose soft point, 286 grain. cca 700 m./s.
Never failed.
In a first example, of roe deer, animal is soft skinned, and velocity is moderate.
In a second example, wild boar, animal is tough, but bullet is slow velocity.
So, till now, 20 years of hunting, it never failed.

Now about failure that I witnessed.
I was stalking with a friend, he had 8x57 (8mm mauser), cartridge 8x57 Sellier Bellot 196 grain, SPCE (soft point cutting edge), known to be one of the cheapest on the market (and thus popular).
He hit the roe buck at around 80 meters, DRT, heart lung area, and we took animal at my house for skinning.
Bullet completely disintegrated, destroying lung and heart. We found few pieces of jacket, no exit wound.

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