Understanding The Phenomenon Of Jacket-Core Separation

[Hunter-Habib]

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,
Habib

 

[Ontario Hunter]

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.

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.

 

[Ontario Hunter]

Site is really a mess today and not letting me attach the third photo for some reason. This is Partition slug from third gemsbuck also less than one hundred yards. A lot more lead retained on this Federal factory load vs my home loads with same bullet.

 

[PHOENIX PHIL]

Only once that I know of. It was a 140gr Nosler Ballistic Tip. Quartering away shot at about 250 yards on the diminutive Coues deer here in Arizona. It traversed through from left somewhere in the ribs where it entered to just behind the right shoulder where the rest of the bullet was in one piece.

The deer dropped in its tracks and never flinched. I do not consider this a bullet failure as the BT's are meant to expand quickly and intended use is on smaller game. In this case a perfect example of how effective the bullet is in it's proper use case.

Were I use to use that bullet on larger animals and in worse situation where the animal was at say 100 yards and impact velocity much higher, it could've meant for a lost animal. Still I wouldn't consider that a bullet failure, I'd consider that the hunter's failure to not use a more proper bullet for the use case.

 

[PHOENIX PHIL]

Let me take that back. I did shoot a mule deer doe many years ago where the bullet broke roughly in half on impact. The one half skittered down the onside rib cage and exited. There were two holes on the same side of the deer yet the terrain was open, it didn't hit anything until it hit the deer.

The other half continued on and put a small hole in the left lung and the top of the heart. The deer meandered off just a little ways and dropped I'd say mostly due to the wound in the heart. Dead deer found shortly, but in this case I'd say it was a bullet failure.

It was a Sierra boattail and I've never hunted with that bullet again.

 

[poco]

I’m an ammo hoarder and bought a large supply of .270 win , .303 British, .300wm , 375 , in various brands, all of my ammo seems better structured/ bonded then any of the newer variants the ammunition companies offer now
the .270 ( 150) , .300wm (180) , 375 ( 270) are all federal classsic(inter bond), the .303 (180) Remington cor-loc all where deadly and tough and didn’t suffer core separation on nilgai, aoudad, caribou , bear, deer ,
sadly the new federal are loaded with Speer hotcore and don’t hold up as well , but do kill well when heavy for caliber is used .
I also was a tester for the original Barnes X which didn’t preform well till it was redesigned to the tsx/ ttsx
the new trend seems to be thin walled cup and core ( eldx Berger) ect, and I personally think they are garbage on medium sized game , usually 100% core separation in any caliber or speed

 

[PerH]

I haven’t experience in that field since I’ve used mostly bonded bullets . But in two occasions I would rather had a different bullet .

but when speaking about the Partion it is several differences in the old and newer models of them to it’s a coincidence. When they altered the metallic in them from cold to warm extrusion it completely changed it , and it showed why NP became a cuss word over here by some .

NP btw was a borrowed design or independently discovered stateside I think term can be of the old German HMantel . As it’s shaped like a H and similar like a NP it have much of same , but it also looses the jacket and core and don’t behave so stressful on game as one think it is .

Since it was made of Nickel steel and that type is harder than other steel so expansion goes slower and in a different patterned fashion . If it divides into two it do so slower and more predictable.

 

[Sh1kar]

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,
Habib

Couple of comments

Winchester Silvertip a notoriously shocking round for Africa. Way too soft

The Nosler partitions I have used to a bullet always ended up looking exactly like those in post 2. I considered this a good thing. Big initial wound channel as it separates then a further penetration with the core lokt base. Happy to use in PG but probably not in Buff

S

 

[John Wasmuth]

I don’t consider it as “Bullet Failure” since the end result is a dead animal even though the core has shed its jacket. I think I’ve only seen it when I’ve had the velocity over what the bullet was designed to handle. Back years ago I tried to always use Barnes Originals. Their 200 grain 8mm bullets had really thick jackets that held together well.

 

[Sika98k]

I used a box of Privi Partisan 7x57,173gr ammunition in Namibia 5 years ago. My own ammunition got waylaid on our journey. Being 400kms from Hosea Katuko it wasn’t worth waiting until the next day or driving back later.
i picked up a box in a small gun store in Grootfontein. It was significantly slower than my own and required a few clicks of elevation.
Apart from that it did what it said on the label.Last year I used S&B 173gr SPCE, soft point cutting edge. Postmortems showed the bullets pretty well came apart. I lost one oryx which was very annoying. My guide turned to me after the shot and said good shot. We both heard the solid slap of the bullet in the heart/lungs area. Front legs out and took off into the distance. . Nosler Partition or Norma Oryx any day in preference. I used the remainder on deer here at home last season. Any bullets I recovered, usually from a frontal shot into the thorax were separated.

 

[375Ruger416]

Tagged for interest.

Not much experience compared to most of you, so take this with a grain of salt. Seems jacket core separation is a risk with ANY cup and core bullet. Use with caution on any game in which deep penetration is required.

Bullet failure on the other hand, only occurs if there is poor terminal performance. Can be a combination of ammo/game selection, shot placement for a given type of animal, or pure bullet mechanical failure (all manufactured things can fail).

I like monometals for everything except varmints. For longer distances, I’d prefer a lead bullet with controlled expansion by bonding or mechanical jacket (accubond, ELD-X etc). The downside of a controlled expansion bullet seems to be that the terminal effect may not be as dramatic. However, a bullet that fails to reach the vitals is simply ineffective. Other than big cats where a partition or similar seems to be ideal in order to have rapid expansion AND deep penetration (just in case), the Swift A-Frames and Barnes TSX/TTSX seem to be the closest examples of one bullet for everything that exist.

Now, keep in mind I’ve only taken coyotes, Whitetail deer, moose, and pronghorn so far. I like the idea of rapid expansion and massive tissue destruction leading to a humane kill, but only if shot placement and ADEQUATE penetration are guaranteed. So, I’ve decided to prioritize accuracy and penetration and plan to use Barnes TSX and LRX bullets on my plains game hunt in Namibia this fall.

 

[grand veneur]

Jacket-core separation was earlier considered as normal. It did not bother us that much because we were working with much bigger calibers and heavier bullets compared to nowadays.

Here for example are bullets caliber 458 500gr RN SP from buffalos.

 

[375Ruger416]

Jacket-core separation was earlier considered as normal. It did not bother us that much because we were working with much bigger calibers and heavier bullets compared to nowadays.

Here for example are bullets caliber 458 500gr RN SP from buffalos.

View attachment 598705

Yes, using a larger cartridge and heavy for caliber bullets seems to cover over this weakness for sure.

 

[Hunter-Habib]

Some very interesting field experiences from all the commenters.

 

[tarbe]

To answer the OP question: No. Not always a failure.

Partitions do not rely on front core retention for performance.

Completely losing the front core is accepted, and even considered preferred on the non-DG bullets.

The front half is generally designed to create the wide wound channel, knowing that the back half will always remain intact and penetrate deeply.

So having medium-game intended Partitions blow the front is not a failure. It is allowed by design.

It may not always happen, depending upon caliber, weight, impact velocity, resistance met.

 

[AimSmall]

The evolution from round lead balls to cup-n-core went along with greater muzzle velocities. I think these bullets were ok at speeds in the low 2,000's, but once they got over 2,500-2,700 coming apart was an issue. Now, with 'magnum' being normal, bullets have to be tougher to withstand impact at speeds close to and above 3k fps.

I did witness a moose being shot on the shoulder with a 300 mag at about 125yds... after the moose got up and ran off, never to be found, we learned the hunter was using a Ballistic Tip... I'd speculate a tougher bullet would have been a better choice.

On the other hand, I've seen dozens of deer DRT with Sierra gameking and Nosler BT, but at slower bullet speeds. The core was often seperating or seperated.

So, Habib, my answer would be "it depends".

Lucky we are to have so much experience to draw from on this site.

 

[deewayne2003]

I've seen numerous jacket and core separations that were discovered while cleaning dead whitetail deer and feral hogs, however I would not classify them as failures because the game animal was killed quite effectively. These separations usually occur at close distance and high impact velocity is usually the cause for the separation and also resulted in BANG FLOP.

Now having said that I have witnessed several absolute failures.....

130gr Sierra Game King .270win - Shot a LARGE whitetail doe in the shoulder at 125yds distance; she was found dead in a creek 50yds from where she was shot. I was hunting with a doctor that owned the property and while skinning we discovered that the shoulder blade was broken but ZERO damage to the vital organs. After closer look we realized that cause of death was DROWNING after she fell into the creek.

180gr Balistic Silver Tip .300win - While hunting with my cousin I watched him nail a LARGE whitetail buck in the shoulder broadside at 100yds, I was watching in my binoculars when he shot and I'll never forget the massive cloud of hair that blew off this bucks shoulder blade upon impact and watched as it ran off with its left front left bobbing around but otherwise looking quite healthy - we found no blood but tons of hair all over the ground and the buck was never found.

Same stand, same ammo a couple of hours later and a 350lbs+ pig comes out and same thing - Good hit but no blood and pig not found.

The following evening my cousin was hunting another stand close to me with same rifle and ammo. I hear my cousin shoot and he dropped a MASSIVE 8pnt that was standing in tall grass by shooting it in the head just under the left eye.

You would think that a 180gr Balistic silver tip .300Win @ 70yds with a head shot would blow the skull up like a ripe melon..... but no, there was the perfect entrance wound under the left eye and blood coming out it's ears - NO EXIT WOUND!

 

[poco]

The evolution from round lead balls to cup-n-core went along with greater muzzle velocities. I think these bullets were ok at speeds in the low 2,000's, but once they got over 2,500-2,700 coming apart was an issue. Now, with 'magnum' being normal, bullets have to be tougher to withstand impact at speeds close to and above 3k fps.

I agree 100%
in the 1990’s I was deeply involved in nilgai hunting and the ranch had a minimum caliber requirement of 7mm , so the joining neighbor bought a custom made 7mm STW
it was a complete failure on nilgai, with lots of bullets never reaching vitals/ exploding on impact, this probably could have been cured if a mono was developed at the time
@ 3300 fps the stw imo was just too fast for thick skin medium game with a C&C

 

[skydiver386]

I've seen plenty of what some might describe as a failed projectile, but often still resulted in a rapid kill, sometimes not so rapid. Broadheads that snapped in half when even light bone was struck, bullets that expanded to wide, to rapidly and failed to penetrate vital organs, etc. Even one example of a Match type bullet that was shot at a deer, penetrated completely but resulted in a long blood trail. When asked about the choice of projectile the hunter stated it was a BTHP Match, so why wouldn't it work?

In all, bullet failure is rare nowadays given the wide range of velocities, twist rates and game animals we hunt. Designing a bullet for the 30-30 and Eastern Whitetail deer would be simple compared to what would have to be taken into consideration now.

 

[Ontario Hunter]

It depends on priorities. For bang-flop a Partition is excellent on plains game size critters. Often not so excellent when the skin comes off. On this side of the pond I've always been conscious of meat damage. It's the way I was raised. Or more accurately, the way my dad was raised during the Great Depression (aka the Dirty Thirties up here in Canada). Briefly during the late seventies I experimented with 165 gr CoreLok 30-06. Not impressed with knockdown and definitely unimpressed with meat damage. Our family was counting on that meat, especially when I was in college. So I went back up to 180 gr loads. As a big timber stalker my shots were never long anyway. Big slugs moving at moderate speed impact hard and don't make a mess. They don't reach way out there but what's the fun in that?