Bullet Blow Ups

[fyrewall]

In an earlier post, received from a Berger bullet ballistic engineer and from looking at Sg calculations the length of the plastic tip is subtracted - JBM - calculations - stability. Apparently, JBM and others think that the plastic tip being much lighter than the other parts of the bullet has no effect in moving the bullets center of mass forward. JBM, using the Miller stability calculator, has provisions for plastic tip length. I think there is some validity for the subtraction of the plastic tip length because my use of the 75 grain Amax and ELDM in 7.7 & 8 twist barrels has worked out real well at all ranges. Measuring the entire works gives an Sg in the marginal stability range; not that Sg values are an absolute indicator of stability but certainly provide a good indicator. Pursuing this point (pun?) further the Berger stability program shows that optimum ballistic performance is derived from a certain relationship between bullet length and twist rate. The same stability indicators are to be found in the Hornady 4 degree calculator.

Adding tin to the core alloy would make that alloy sort of a solder - sticky upon heat. Brass, an alloy of copper and zinc, is electro-plateable and jacket alloy should be similar. I remember shooting some Remington Power Lockt (??) bullets that were electro plated then had the points modified to make a shallow hollow point having expansion cuts up near the bullet point. The point of all this being to make a lead core bullet sort of a semi monolithic type, this might mitigate some bullet blow-ups.

I am in complete agreement on the patent business - a family member came up with about 100 patents for various organic chemical processes with the expectation that some serious big fund research would run into one of his patents requiring some buy out. As far as I know, he never got a hit. Sort of like traps around some eatable goodie to trap a wolf.

 

[DaveTooley]

Most of the time it's about heat. This was shot at 10 yds.
I'll add that in this particular case 80% of the fractures were associated with the same two lands. I shot probably 30 or more shots all with the same results.

 

[243winxb]

Most of the time it's about heat.

Had some 80gr ,243 win, lead tipped bullets make marks on a target at 100 yards like your photo. A barrels large groove diameter produced blow by. More of the 4000 degree heat got past the bullets on firing. Air friction kept the tip melting.

Same barrel would not group till 10 fouling shots were fired. The old Rem 70 gr match bullet key holed on target @ 100 yds. . Amazing 3" -3 shot group.

 

[fredo]

Still here.

Some thoughts - do long and heavy for caliber hunting bullets blow up when shot at velocities of about 3000 or more?; do long and heavy for caliber bullets, of any jacket type, hunting or match, shot from 6.5 CM or 6.5X47L at "safe" MV's blow up?

You need to realize that, RPM is product of both velocity and barrel twist rate. Therefore, one cannot arbitrarily assign a "blow up" velocity for any bullet, without first factoring barrel twist into the equation...

When you take Mr. Tooley's comment that HEAT is a contributing factor to bullet failure, heeding RPM calculations makes perfect sense.

An increase of bullet RPM leads to more heat generated, due to friction. Combine that with the rotational stress that a fast twist barrel imparts on a bullet's jacket, and you compound the potential for failure...

In case you don't know, you calculate RPM by multiplying velocity by the constant 720, then divide the product by barrel twist.

If you're not solving for RPM when pondering bullet failure, you're missing a very big piece of the puzzle...

 

[RGRobinett]

Matt, you are right material changed from c21000 which is true 95-5 to c 22000 which is 90-10 plus or minus 1% on both with traces of lead less than .05 % for both..

Yes - when I've had the materials analyzed, the J4s have always come back between 90:10 & 92:8;
Sierra 95:5. I have not had the Hines jacket checked, as my "checker" changed jobs/states.


Annealing J4 jackets, for some applications, has proven useful relative to topic. George has provided
guidance regarding temps, hold time, etc, which have [mostly] eliminated bullet failures. As stated, by Dave Tooley, and other earlier, there is no single cause - sometimes, it just the barrel, something else, or, a combination . . .

Many seasons back, a pal and I purchased a pair of barrels - identical twins, from the same litter - and I chambered them using the same reamer: same day, same components, as soon as the chronograph read 2800 FPS, his barrel (which I called The Bullet-Wrecker) "blew-up" every bullet (6mm, they were), while mine never destroyed a bullet - not even at velocity (PRESSURE) which destroyed cases via a single firing . . . and that was just short of 3200FPS.

I was unknowingly involved the Berger's, "thick jacket" testing, as Bill Niemi (then Berger/J4s die maker) knew of my involvement with The Bullet-Wrecker, and had me subject various 6mm test bullets to a trip down that barrel - interesting times.

Only a few years later did Bill inform me of my indirect involvement. Many of the bullets (many brands/types), which did not, "blow-up", after exiting that barrel, passed through the 200 Yd. target spewing lead vapor. In that barrel, Moly plating the various bullets reduced bullet failure from 100% to 10% - certainly not a cure, but evidence of cheap insurance, and that friction is a culprit. RG

 

[RGRobinett]

you have to include the plastic tip in equation for stabilization rate so 8 twist in 6mm really isn't to far off. I would like to see a small amount of tin added to cores and then try and find a way to speed up galvanic process either with low heat or electrically. remember all blow ups are not only jacket related...

George, being pretty much an [ballistic] idiot, I have made a good many bullets using cores which were a much as 3% antimony and 0.5% tin - they all shot, "like the hammers of hell" - that is, as well as 1/2 -1.0% antimony cores in the same jackets. I used them mostly for hunting/testing . . . may have been a little hard on the core-form die??!?? RG

 

[RGRobinett]

Most of the time it's about heat. This was shotView attachment 1068203 at 10 yds.
I'll add that in this particular case 80% of the fractures were associated with the same two lands. I shot probably 30 or more shots all with the same results.

Dave - that's what Tom and I observed testing THE Bullet-Wrecker (see above), but, at 200 Yd/!!
The swirls were larger, and not as intense, but, none-the-less, there. Thank you for sharing the pic! RG

 

[DaveTooley]

Dave - that's what Tom and I observed testing THE Bullet-Wrecker (see above), but, at 200 Yd/!!
The swirls were larger, and not as intense, but, none-the-less, there. Thank you for sharing the pic! RG

Randy those bullets shot on that target didn't make it 50 yds. Interesting you still had lead spewing at 200.
There's just too many contributing factors to narrow it down to two or three.

Question
I don't recall ever losing a bullet made on a Sierra jacket. What's been your experience?
In hindsight I think every jacket I ever got from Sierra over the years had been annealed.

 

[geo.ulrich]

Question
I don't recall ever losing a bullet made on a Sierra jacket. What's been your experience?
In hindsight I think every jacket I ever got from Sierra over the years had been annealed.[/QUOTE]
Exactly all the long range ones any way I don't remember if they anneal the short range theres one step less in the drawing process... j4's no annealing at all unless you do yourself ...

 

[Homerange]

Interesting discussion guys.

Doesn't it seem counter-intuitive that an annealed projectile would resist blowup more than a work hardened/tougher jacket ?
What am I missing ?

 

[geo.ulrich]

Interesting discussion guys.

Doesn't it seem counter-intuitive that an annealed projectile would resist blowup more than a work hardened/tougher jacket ?
What am I missing ?

Drawing material back before bullets are made the material will Slightly work harden during swaging operations, a hardened jacket already has stress built into it and just becomes harder leading to failures sometimes..

 

[RGRobinett]

Randy those bullets shot on that target didn't make it 50 yds. Interesting you still had lead spewing at 200.
There's just too many contributing factors to narrow it down to two or three.

Question
I don't recall ever losing a bullet made on a Sierra jacket. What's been your experience?
In hindsight I think every jacket I ever got from Sierra over the years had been annealed.

Dave, my bad - those 'spewing lead' were at 100 Yd. - not 200 per my original post. As on your test/target, we fired at individual aiming points: the bullets which survived were amazingly close to same impact, when considering that about 90% were failing to reach the target. RG

 

[RGRobinett]

Interesting discussion guys.

Doesn't it seem counter-intuitive that an annealed projectile would resist blowup more than a work hardened/tougher jacket ?
What am I missing ?

I believe the key here is not interchanging/confusing harder with tougher - definitions.
Annealed (drawn back) J4 jackets, are what I'd call tougher than the work-hardened, out of the bucket product.

Following drawing back, one can cut some longitudinal slits, to about mid-length, in the jackets, grab a 'petal', and bend it down to the base, then back up to the beginning point: a drawn back J4 will withstand about 7-8 cycles; out of the bucket, 2-3 (tops). The hardness, I believe equates to brittleness - the malleability, to toughness. But, I've been wrong B4! RG

 

[Homerange]

I believe the key here is not interchanging/confusing harder with tougher - definitions.
Annealed (drawn back) J4 jackets, are what I'd call tougher than the work-hardened, out of the bucket product.

Following drawing back, one can cut some longitudinal slits, to about mid-length, in the jackets, grab a 'petal', and bend it down to the base, then back up to the beginning point: a drawn back J4 will withstand about 7-8 cycles; out of the bucket, 2-3 (tops). The hardness, I believe equates to brittleness - the malleability, to toughness. But, I've been wrong B4! RG

Yeah I get that but jackets made from guilding metal, brittle ?
Nah, that I don't swallow.

Annealed then quenched might be a different matter like one might do for carbon steels.
Bullet blow ups have been around for decades and the first I read about them was early 70's when the 220 Swift was getting popular as many bullet manufacturers hadn't had to consider such stresses on projectiles much before that. Jackets were made tougher and cores too from better/optimized alloying.
One still need select the right pill for the job so anything designed for appropriate terminal performance on game might be insufficiently robust to withstand the high rotational forces at high velocities, barrel imperfections excluded.
I've used a few 'petaled' projectiles and they're certainly not what I would choose to stoke hard !

 

[DaveTooley]

Yeah I get that but jackets made from guilding metal, brittle ?
Nah, that I don't swallow.

Annealed then quenched might be a different matter like one might do for carbon steels.
Bullet blow ups have been around for decades and the first I read about them was early 70's when the 220 Swift was getting popular as many bullet manufacturers hadn't had to consider such stresses on projectiles much before that. Jackets were made tougher and cores too from better/optimized alloying.
One still need select the right pill for the job so anything designed for appropriate terminal performance on game might be insufficiently robust to withstand the high rotational forces at high velocities, barrel imperfections excluded.
I've used a few 'petaled' projectiles and they're certainly not what I would choose to stoke hard !

Brass work hardens when formed. Over time case necks become brittle and split. Cartridge case heads get harder by extra draws when forming which leads to annealing the front third of the case to relieve brittleness. Jackets are no different. No heat required.

 

[DaveTooley]

I believe the key here is not interchanging/confusing harder with tougher - definitions.
Annealed (drawn back) J4 jackets, are what I'd call tougher than the work-hardened, out of the bucket product.

Following drawing back, one can cut some longitudinal slits, to about mid-length, in the jackets, grab a 'petal', and bend it down to the base, then back up to the beginning point: a drawn back J4 will withstand about 7-8 cycles; out of the bucket, 2-3 (tops). The hardness, I believe equates to brittleness - the malleability, to toughness. But, I've been wrong B4! RG

Leads me to say what I've thought for quite awhile. I think we are getting microfractures on the ogive.

 

[geo.ulrich]

Leads me to say what I've thought for quite awhile. I think we are getting microfractures on the ogive.

On the C22000 material being a finer grain ie. harder to start yes not on the C21000. this is why you don't see the issue with the Sierras. All that drawing the jackets does is grow the grain size..which in turn makes them somewhat softer but not completely dead soft. which is a different conversation..

 

[RGRobinett]

Yeah I get that but jackets made from guilding metal, brittle ?
Nah, that I don't swallow.

Annealed then quenched might be a different matter like one might do for carbon steels.
Bullet blow ups have been around for decades and the first I read about them was early 70's when the 220 Swift was getting popular as many bullet manufacturers hadn't had to consider such stresses on projectiles much before that. Jackets were made tougher and cores too from better/optimized alloying.
One still need select the right pill for the job so anything designed for appropriate terminal performance on game might be insufficiently robust to withstand the high rotational forces at high velocities, barrel imperfections excluded.
I've used a few 'petaled' projectiles and they're certainly not what I would choose to stoke hard !

Think relative. RG

 

[RGRobinett]

Question
I don't recall ever losing a bullet made on a Sierra jacket. What's been your experience?
In hindsight I think every jacket I ever got from Sierra over the years had been annealed.

Exactly all the long range ones any way I don't remember if they anneal the short range theres one step less in the drawing process... j4's no annealing at all unless you do yourself ...[/QUOTE]

George, yes, The Bullet Wrecker worked quite well on Sierra Match King bullets (I believe they were a 107 Gr.) - nearly 100% failures. The only (bare/no coated) bullet which would survive a trip through that barrel was the 105 Gr. LAPUA Scenar. Regrettably, a few weeks ago, when I asked Tom if I could have that barrel, he informed me that it had, "gone to the dump". For bullet integrity, it was a good test platform. RG

 

[fyrewall]

You need to realize that, RPM is product of both velocity and barrel twist rate. Therefore, one cannot arbitrarily assign a "blow up" velocity for any bullet, without first factoring barrel twist into the equation...

When you take Mr. Tooley's comment that HEAT is a contributing factor to bullet failure, heeding RPM calculations makes perfect sense.

An increase of bullet RPM leads to more heat generated, due to friction. Combine that with the rotational stress that a fast twist barrel imparts on a bullet's jacket, and you compound the potential for failure...

In case you don't know, you calculate RPM by multiplying velocity by the constant 720, then divide the product by barrel twist.

If you're not solving for RPM when pondering bullet failure, you're missing a very big piece of the puzzle...

Sorry for not being more explicit - I made the assumption that any given bullet would need to be stabilized with the correct twist, thus a real long pointy bullet would require a faster twist and that same twist would stabilize the same bullet for both a 6.5X47 Lapua velocities or a 6.5-.284. I am unaware of any assigned "blow up" velocities for any bullet but stuff happens and bullets apparently do blow up. I should have asked: has any 6.5X47 Lapua or rifle of equivalent velocities of about 2650 fps ever blown up a long pointy bullet of weighing 140 grains or more? Would some higher velocities get into the danger zone for that particular bullet and twist?. Assuming adequate stability/twist, would velocities where blow ups occur be regarded as some velocity failure zone for a particular bullet .

My final thoughts on the entire problem (abstract by amateur): Certain long pointy bullets requiring fast twists for stabilizing are more prone to bullet blow ups at certain velocities at velocities somewhat near 3000 fps. The blow ups occur just feet beyond the bullet launch point at the muzzle. These long pointy bullets are subjected to pitch, yaw and precession and undergo a transition before final stabilization. These bullets undergo rotational stresses caused by fast twist barrels, heat, and the above mentioned pitch, yaw and precession. Any jacket weakness is exasperated by the preceding stresses and these jacket weaknesses may be caused by excessive hard working the jacket during forming which would make for a tougher jacket but could introduce failures in the jacket. A solution might be additional jacket annealing during the jacket forming process. These jacket failures would likely occur where the land engraved the bullet but be started at the ogive area. I think excessive work hardening might introduce longitudinal weak areas (expansion cracks) in the jacket ogive ending at the bullet tip.

Almost all stubby varmint type bullets can be driven blazing fast, some up to 4,000 fps without blowing up. These same bullets may be subjected to faster than needed twist rates and yet do not blow up. I have used 53 grain Vmax bullets at 3750 fps from a 8 twist .22-.250 with adequate accuracy without them blowing up. The suggested twist rate for the 53 Vmax is 12. About 4 years ago, in this same forum, there was a discussion of plastic tip and hollow point bullets in regard to bullet center of mass ( new stability requirements) - apparently the air voids and plastic tips might make a bullet longer but mitigate the requirements for faster twists needed for stability.

Sectioning these stubby (short range) bullets shows jacket thicknesses comparable or thinner than those in long pointy match type bullets. Many of the stubby bullets have longer bearing surfaces and comparatively shorter ogives. These stubby bullets are designed for high velocities, have thin jackets to enable target destruction and having a precise center of mass crosswise can be driven at real high velocities with adequate accuracy without blowing up. Again, I think the reason is the absence of the degree of yaw, pitch, and precession that the real long pointy match bullets are subjected to.

Dave's 4 bullet hole photos and 30 shot test sure are interesting, extremely fast bullet spinning of some unknown bullet at some unknown velocity. This seems to indicate failures at the same point. Using some assumption of 270,000 rpm (3000 fps and 8 twist), I am amazed that the failure points were so uniform. Could these bullet failures be the result of predictable down range yaw and precession effects independent of assigning the failure to a specific land and almost exact bullet positioning and RPM's probably over 250,000?

Too bad the "Bullet Wrecker" was tossed. Without that important part, the barrel, these observations could be dismissed as anecdotal. Apparently, up-to date technology such as in-flight photos of failing bullets and x-ray photos of bullets have not been part of all this. Bore scope photos are not available.

The Berger bullet blowup torture test using 6.5 bullets in a .001 inch larger than normal .256 land 6.5 barrel, blew up bullets. Their solution was thicker jacket bullets.