Bullet Blow Ups

[DaveTooley]

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?

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.

The Berger bullet blowup torture test using 6.5 bullets in a .257 bore apparently used a better barrel than the "Bullet Wrecker".

140 Gr. flatbase bullets @2850-2900 fps in an 8.5 twist. Nothing extreme there considering this barrel and two others performed great with the first lot of bullets.

 

[fyrewall]

140 Gr. flatbase bullets @2850-2900 fps in an 8.5 twist. Nothing extreme there considering this barrel and two others performed great with the first lot of bullets.

Thank-you for your patience --- sounds like some type of hunting bullet -- that should not have happened -- bad lot? -- where these bullets intended for 6.5X55 @ 2600 fps or so?

 

[DaveTooley]

Custom made BR bullets. I found all test targets. More like 200 shots trying different things.
I'll say this one more time. First lot of bullets. Three rifles, three different people. No problems. We were delighted with the results. Next lot of bullets nothing but problems in those three rifles.

 

[fyrewall]

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.

That was a real valuable photo, but I would like to make some comments:

View attachment 1069135

Attached is a spread sheet containing some simple calculations.



10 Yards is a real short range, the time of flight is .011 seconds (Hornady 4DOF) for their 140 Hpbt @ 2850 fps at 10 yards. The bullet rotations would range from 241,412 to 243,529 RPM depending on velocities that might range from 2850 to 2875 (this was carefully explained to me by Fredo). The given barrel twist is 8.5. What are the extreme velocity spreads for your ammo? Taking a look at my calculations the number of turns expected at paper impact; 2800 fps = 43.48, 2803 fps = 43.53, 2807 = 43.59, 2825 fps = 43.87, 2850 fps = 44.26, 2875 fps = 44.65. What is a rotation? a complete 360 degree turn. For a fractional turn like 44.65 - 44.26 = .39; 360 * .39 = 140 degrees.

RPM's of about 240,000 are really spinning, time of flight before target impact is short, about .00001833 minutes. Just a very tiny little variation in velocity would not affect the TOF but would have a big affect in a specific point of the bullet's circumference hitting the target. Thus, respectfully, I think your thinking that the core rupture points are at specific land positions is incorrect.




This diagram shows pitch and yaw and the affects of precession (spinning stuff tends to move at 90 degrees when the direction from which it is pushed). Your photos sort of tuned me into the cause of your very uniform lead rupture points. It appears to me that the rupture points are located at about 11 and 5 o'clock and that would fit the diagram that shows the location of a bullet tip undergoing yaw, pitch and precession prior to "going to sleep" this would be somewhat down from the outside of the cone. The point of the bullet would be wobbling prior to target impact and this wobbling would exert maximum stresses on the bullet. Shorter bullets, provided that they have adequate jackets seem to resist "blow ups" well.



This is a .243 87 Hornady V Maximum (VMax) bullet. I shoot these with great confidence out of my 6mm rifles that are all 8 twist. When I really need to get better results at long range I switch to 105's. Note the thin jacket that handles velocities near 3400 from a 6mm AI. This is a great rodent bullet - it blows up only when hitting the rodent.

Lead:

Lead is really a very weak metal and has extremely low tensile strength, low elasticity, soft, easy to form and shows creep even at temps somewhat greater than room temps. I think that lead, in the process of grain size changes might have uneven grain growth and further strength reductions. I respectfully, disagree that bullet cores melt within a TOF of .011 seconds and think the lead swirl marks deposited on the target are lead particles ripped from the lead core by yaw, pitch, precession and centrifugal forces that have caused bullet jacket failure and exposure of the lead core. I have never ever seen evidences of molten lead in bullets recovered from any target. Core and jacket fragments yes but a bullet core weighing over 120 grains or so turned into a liquid would sure be noticeable - the TOF is too short for heat to get into the bullet and melt the core.

 

[Dusty Stevens]

That was a real valuable photo, but I would like to make some comments:

View attachment 1069135

Attached is a spread sheet containing some simple calculations.

View attachment 1069137

10 Yards is a real short range, the time of flight is .011 seconds (Hornady 4DOF) for their 140 Hpbt @ 2850 fps at 10 yards. The bullet rotations would range from 241,412 to 243,529 RPM depending on velocities that might range from 2850 to 2875 (this was carefully explained to me by Fredo). The given barrel twist is 8.5. What are the extreme velocity spreads for your ammo? Taking a look at my calculations the number of turns expected at paper impact; 2800 fps = 43.48, 2803 fps = 43.53, 2807 = 43.59, 2825 fps = 43.87, 2850 fps = 44.26, 2875 fps = 44.65. What is a rotation? a complete 360 degree turn. For a fractional turn like 44.65 - 44.26 = .39; 360 * .39 = 140 degrees.

RPM's of about 240,000 are really spinning, time of flight before target impact is short, about .00001833 minutes. Just a very tiny little variation in velocity would not affect the TOF but would have a big affect in a specific point of the bullet's circumference hitting the target. Thus, respectfully, I think your thinking that the core rupture points are at specific land positions is incorrect.


View attachment 1069139

This diagram shows pitch and yaw and the affects of precession (spinning stuff tends to move at 90 degrees when the direction from which it is pushed). Your photos sort of tuned me into the cause of your very uniform lead rupture points. It appears to me that the rupture points are located at about 11 and 5 o'clock and that would fit the diagram that shows the location of a bullet tip undergoing yaw, pitch and precession prior to "going to sleep" this would be somewhat down from the outside of the cone. The point of the bullet would be wobbling prior to target impact and this wobbling would exert maximum stresses on the bullet. Shorter bullets, provided that they have adequate jackets seem to resist "blow ups" well.

View attachment 1069141

This is a .243 87 Hornady V Maximum (VMax) bullet. I shoot these with great confidence out of my 6mm rifles that are all 8 twist. When I really need to get better results at long range I switch to 105's. Note the thin jacket that handles velocities near 3400 from a 6mm AI. This is a great rodent bullet - it blows up only when hitting the rodent.

Lead:

Lead is really a very weak metal and has extremely low tensile strength, low elasticity, soft, easy to form and shows creep even at temps somewhat greater than room temps. I think that lead, in the process of grain size changes might have uneven grain growth and further strength reductions. I respectfully, disagree that bullet cores melt within a TOF of .011 seconds and think the lead swirl marks deposited on the target are lead particles ripped from the lead core by yaw, pitch, precession and centrifugal forces that have caused bullet jacket failure and exposure of the lead core. I have never ever seen evidences of molten lead in bullets recovered from any target. Core and jacket fragments yes but a bullet core weighing over 120 grains or so turned into a liquid would sure be noticeable - the TOF is too short for heat to get into the bullet and melt the core.

Im not an expert by any means but i would venture to say that the same barrel will turn a bullet the same number of rotations at a given distance no matter what the velocity is. Im not arguing for sure because you did a lot of research there so i hate to bring it up

 

[Ned Ludd]

Im not an expert by any means but i would venture to say that the same barrel will turn a bullet the same number of rotations at a given distance no matter what the velocity is. Im not arguing for sure because you did a lot of research there so i hate to bring it up

Edited to correct mistake: Dusty is correct. Bullet rotation in terms of RPM is proportional to linear velocity. The total number of bullet turns that occur within a given distance is dependent on rotational velocity and the time the bullet takes to cover that distance. A bullet with greater velocity will be spinning faster but it will also have a shorter TOF, so the number of turns within a given distance should be the same.

 

[Dusty Stevens]

Bullet rotation in terms of RPM is proportional to linear velocity. The total number of bullet turns that occur within a given distance, therefore, is also dependent on velocity.

Realistically however, the magnitude of velocity changes we are often concerned with might be as small as 10 to 20 fps or less. As a relatively small fraction of the total velocity, typical velocity variance values of <0.1% mean only that the difference in the number of turns at some specific distance due to velocity variance will also be very small.

So are you saying a bullet shot from an 8 twist barrel doesnt turn the same exact number of times at the exact distance no matter if the velocity is 4000fps or 32fps? Where does the bullet slip during a change in velocity?

 

[jo191145]

What am I missing?
Why would anyone think making a jacket softer would help it hold together?

 

[dcali]

What am I missing?
Why would anyone think making a jacket softer would help it hold together?

Because the heat transfer through the jacket is a highly uncertain process and depends on a lot of things we don't understand fully. It's not crazy to wonder if a softer jacket could decrease friction. There could be other reasons, but that's all I can think of.

 

[dcali]

So are you saying a bullet shot from an 8 twist barrel doesnt turn the same exact number of times at the exact distance no matter if the velocity is 4000fps or 32fps? Where does the bullet slip during a change in velocity?

The bullet's initial rpm is determined only muzzle velocity and twist. But since aerodynamic coefficients, including the spin damping coefficient that determines how quickly a bullet's rpm slows, change with velocity, it won't be *exactly* the same.

 

[jo191145]

Because the heat transfer through the jacket is a highly uncertain process and depends on a lot of things we don't understand fully. It's not crazy to wonder if a softer jacket could decrease friction. There could be other reasons, but that's all I can think of.

A softer jacket is a weaker jacket more susceptible to failure. A softer jacket will leave more copper fouling behind it causing more friction.
Many people have witnessed not using enough lube in the neck after annealing brass. Leaves those bits of brass stuck to the bushing. Same concepts apply to the bore.
I once had a problem with 39 gn Sierras coming apart in flight from a 204 at normal velocities. The thinnest and weakest jacket it the 20 caliber lineup. Every other bullet had no problem. Making it even weaker would logically seem to be counterproductive.
FWIW the nylon tips actually released from the jacket without damaging the little nylon tail that holds them in. I theorized somehow the core was pushing forward in the jacket opening up the meplat. Just a theory but I found no evidence the jacket had shredded.
I’m all for experimental thought processes and such. This path makes no sense to me at all.

 

[dcali]

A softer jacket is a weaker jacket more susceptible to failure. A softer jacket will leave more copper fouling behind it causing more friction.
Many people have witnessed not using enough lube in the neck after annealing brass. Leaves those bits of brass stuck to the bushing. Same concepts apply to the bore.
I once had a problem with 39 gn Sierras coming apart in flight from a 204 at normal velocities. The thinnest and weakest jacket it the 20 caliber lineup. Every other bullet had no problem. Making it even weaker would logically seem to be counterproductive.
FWIW the nylon tips actually released from the jacket without damaging the little nylon tail that holds them in. I theorized somehow the core was pushing forward in the jacket opening up the meplat. Just a theory but I found no evidence the jacket had shredded.
I’m all for experimental thought processes and such. This path makes no sense to me at all.

That sounds very plausible. However, I've learned over the years that in complex situations, sometimes the implausible is actually correct. Jacket hardness, strength, ductility, toughness are all probably relevant, and it would not surprise me to find that there is an optimum combination of all of them.

 

[DaveTooley]

That was a real valuable photo, but I would like to make some comments:

View attachment 1069135

Attached is a spread sheet containing some simple calculations.

View attachment 1069137

10 Yards is a real short range, the time of flight is .011 seconds (Hornady 4DOF) for their 140 Hpbt @ 2850 fps at 10 yards. The bullet rotations would range from 241,412 to 243,529 RPM depending on velocities that might range from 2850 to 2875 (this was carefully explained to me by Fredo). The given barrel twist is 8.5. What are the extreme velocity spreads for your ammo? Taking a look at my calculations the number of turns expected at paper impact; 2800 fps = 43.48, 2803 fps = 43.53, 2807 = 43.59, 2825 fps = 43.87, 2850 fps = 44.26, 2875 fps = 44.65. What is a rotation? a complete 360 degree turn. For a fractional turn like 44.65 - 44.26 = .39; 360 * .39 = 140 degrees.

RPM's of about 240,000 are really spinning, time of flight before target impact is short, about .00001833 minutes. Just a very tiny little variation in velocity would not affect the TOF but would have a big affect in a specific point of the bullet's circumference hitting the target. Thus, respectfully, I think your thinking that the core rupture points are at specific land positions is incorrect.


View attachment 1069139

This diagram shows pitch and yaw and the affects of precession (spinning stuff tends to move at 90 degrees when the direction from which it is pushed). Your photos sort of tuned me into the cause of your very uniform lead rupture points. It appears to me that the rupture points are located at about 11 and 5 o'clock and that would fit the diagram that shows the location of a bullet tip undergoing yaw, pitch and precession prior to "going to sleep" this would be somewhat down from the outside of the cone. The point of the bullet would be wobbling prior to target impact and this wobbling would exert maximum stresses on the bullet. Shorter bullets, provided that they have adequate jackets seem to resist "blow ups" well.

View attachment 1069141

This is a .243 87 Hornady V Maximum (VMax) bullet. I shoot these with great confidence out of my 6mm rifles that are all 8 twist. When I really need to get better results at long range I switch to 105's. Note the thin jacket that handles velocities near 3400 from a 6mm AI. This is a great rodent bullet - it blows up only when hitting the rodent.

Lead:

Lead is really a very weak metal and has extremely low tensile strength, low elasticity, soft, easy to form and shows creep even at temps somewhat greater than room temps. I think that lead, in the process of grain size changes might have uneven grain growth and further strength reductions. I respectfully, disagree that bullet cores melt within a TOF of .011 seconds and think the lead swirl marks deposited on the target are lead particles ripped from the lead core by yaw, pitch, precession and centrifugal forces that have caused bullet jacket failure and exposure of the lead core. I have never ever seen evidences of molten lead in bullets recovered from any target. Core and jacket fragments yes but a bullet core weighing over 120 grains or so turned into a liquid would sure be noticeable - the TOF is too short for heat to get into the bullet and melt the core.

Long range target shooters have been coloring the ogive of bullets for decades with magic markers. This leaves a colored ring around the bullet hole. Easy to identify crossfires or shoot more than one group on a test target. I maked each bullet with a single line. Then I indexed each round in the chamber in the same orientation. I was wrong when I said 8 out of 10 involved two lands. It was 9 out of 10. Do I blame the barrel? Not entirely. I think there are areas of a bullet/core that are prone to overheating. Then add hard jackets that develop cracks in the folds of the ogive and a lot of little insignificant things add up to bullet failure. The military is going to what I would call hyper stabilized bullets . 1-8 twist barrels in a 300 Norma. That's a 215 gr. bullet @ 3050 FPS. I foresee bad things happening.

 

[dcali]

The military is going to what I would call hyper stabilized bullets . 1-8 twist barrels in a 300 Norma. That's a 215 gr. bullet @ 3050 FPS. I foresee bad things happening.

This is puzzling to me. Why aren't they using something more sensible like a 10 twist?

 

[Ned Ludd]

So are you saying a bullet shot from an 8 twist barrel doesnt turn the same exact number of times at the exact distance no matter if the velocity is 4000fps or 32fps? Where does the bullet slip during a change in velocity?

No, you are correct. I was mixing up rotational velocity and number of turns per distance. The faster bullet leaves with greater rotational velocity, but but arrives at the target in less time, so the total number of turns should be the same or very close at a given distance.

 

[Dusty Stevens]

This is puzzling to me. Why aren't they using something more sensible like a 10 twist?

Internet

 

[Dusty Stevens]

No, you are correct. I was mixing up rotational velocity and number of turns per distance. The faster leaves with greater rotational velocity, but but arrives at the target in less time, so the total number of turns should be the same or very close at a given distance.

I knew you wasnt understanding me and knew what you were talking about but i didnt want there to be contradicting info in the archives

 

[Texas10]

So are you saying a bullet shot from an 8 twist barrel doesnt turn the same exact number of times at the exact distance no matter if the velocity is 4000fps or 32fps? Where does the bullet slip during a change in velocity?

This would be true if the bullet were flying straight as a laser, but changes in velocity also change distance to target due to arc in the flight of the bullet. Not a big change at short distances, but of course as the range to the target grows, the arc gets much bigger and so does the flight distance.

Edit to change flight time to flight distance.

 

[DaveTooley]

This is puzzling to me. Why aren't they using something more sensible like a 10 twist?

We're splitting split hairs here but doppler radar data indicates the more extreme designed bullets, VLD's etc, pass through the transonic region better. I've seen the data and in my mind the potential negatives out way the positives. I voiced my opinion but it wasn't my call. I did design the reamers for them.

 

[dcali]

We're splitting split hairs here but doppler radar data indicates the more extreme designed bullets, VLD's etc, pass through the transonic region better. I've seen the data and in my mind the potential negatives out way the positives. I voiced my opinion but it wasn't my call. I did design the reamers for them.

Huh. I had no idea they considered transonic ranges shots (from a norma!!) to be that important. Seems myopic, but I admittedly haven't got a clue about military tactics.