Rotational vs. Kinetic energy...

[DrB]

Don't know that many folks will care, but a member asked what the ratio between rotational and translational kinetic energies are for a bullet.

Here it is, assuming a cylindrical bullet. Ogive and other bullet shapes will decrease it, maybe by as much as half or a bit more for very long VLD type spitzers whereas a HBWC type design would increase it by a bit. This ratio will be in the close ball park, though, order-of-magnitude-wise.

Note that the ratio is constant irrespective of bullet weight or velocity, depending only on caliber and twist length.

Rotational Kinetic Energy/Translational Kinetic Energy = (1/2)*(Pi*C/TL)^2

Where

C = Caliber (in inches, for example)
TL = Twist Length (in inches, for example)
Pi = A circles circumference divided by it's diameter

For example, for a .224 with a 10 inch twist, it turns out that the rotational kinetic energy is about 0.25%, or 0.0025 of the translational kinetic energy. FYI, at 3000 fps with a 60 grain bullet, translational kinetic energy is about 1.625 kJoules (which is about the energy equivalent of a 26 pound lead brick hanging 50 foot up over your head :)). At the same velocity the equivalent height for rotational energy would be about an inch and a half worth of drop.

For a .501 with a 10 inch twist, the answer would be about 1.24%.

Best regards,
DrB

[303Guy]

Thanks for the post. Interesting. That's a little short of what it has been said to be and even less than what I had emagined it might be.

[DrB]

Thanks, 303guy. These results make sense when you consider the surface speed of the rotating bullet, which is just the radians/sec * half the caliber. For 200k rpm and a .224, it comes out to about 200 fps, whereas the bullet may be going more than ten times as fast. Since energy goes as the square of velocity, rotational energy can't be much in proportion to translational.

I ran the numbers some years ago because I was wondering about the "explosive effect" of some high velocity thin skinned varmint bullets, and there had been some fatalities with gyroscopic energy storage... Boeing I want to say, but I don't recall the details. Folks were looking at one and it explosively dissembled.

Anyway, what I found wasn't impressive in itself, as you can see. Varmint al has done a hydrocode simulation hes posted online of one of these kinds of bullets and he demonstrated they were spun past the strength of the lead core, such that just the jacket was holding them together. When the nose tip hits something it starts the rupture of the jacket and dispersion of the core dumping the translational energy in a very short distance. Hence the "explosive effect."

On the other hand, the particles tend to be so small they can't penetrate tissue deeply, so using them on any thick section of a game animal may be bloody but not reach the vitals.

Best regards,
DrB

[geargnasher]

Interesting. Looks like the "explosive effect" is officially debunked one more time. It's also interesting to me that a .30 caliber boolit's rotational to forward energy ratio in flight is about 100:1.

My interest lies in trying to determine the ratio of energy expended between forward and rotational to GET the boolit up to its terminal numbers in the barrel, and to do so one must factor in bearing area of the sides of the lands, force upon that bearing area, coefficient of friction resulting from that interaction, boolit mass, pressure curve, and rate of acceleration to terminal velocity.

In other words, some energy is lost overcoming and accelerating the boolit from a static state of momentum, and there may be a point of diminishing returns when we attempt to shoot a boolit beyond a certain speed in a certain twist gun. The factor that diminishes the returns might well be boolit damage from overstressed engraves, which would explain a lot about the advantages of paper patched boolits and copper jacketed bullets. I'd like to postulate that overstressed engraves affect boolit alignment at muzzle exit in a way that expands group size, rather than affecting the aerodynamics, balance, or gyroscopic stability in a way that expands groups beyond a certain RPM/velocity/peak pressure/pressure curve. But that's a topic for a different thread.

Gear

[Iron Mike Golf]

That tracks with intuition. I am remembering throwing discus and putting shot in high school. Or throwing baseballs and footballs, for that matter,

[leftiye]

I also am interested in the energy (including friction) expended during travel in the barrel to spin the boolit expressed as a ratio as you've done for the resulting rpm/velocity. I have no axe to grind here, it is acceptable that it be negligible.

During some previous discussions on another thread, I had thoughts that are as Geargnasher said - that the bearing faces of the lands, and the boolit might be encountering enough friction to soften or even melt. Most (if not all) of the force to rotate the boolit would be taken on those surfaces which are probly less than .004" wide in most instances. The issues that relate to deformation of the boolit in the barrel have long seemed to me to parallel the symptoms of a weak and or soft metal.

[DrB]

Interesting. Looks like the "explosive effect" is officially debunked one more time. It's also interesting to me that a .30 caliber boolit's rotational to forward energy ratio in flight is about 100:1.
Gear

Well, I don't know about debunking "explosive effect..." :-? that depends on what folks are trying to mean when they say that. All I would say is that liquefying prairie dogs isn't happening directly from the rotational energy. Folks with experience have told me that you can turn a prairie dog into little bitty pieces and soup... I believe them given what I've seen in bigger animals, and p-dog shoot videos.

What I would say is that spinning a bullet faster than the rotational rate that exceeds the strength of the core means that when the jacket ruptures on impact the core turns into an expanding cloud of lead particles. The small particles, because of their high drag to mass ratio, dump their translational energy into the target over a much shorter distance than the intact bullet would. The same bullet if it didn't disintegrate due to RPM might zip right through the target and carry much of it's energy downrange (not necessarily a bad thing, especially on a larger animal -- energy doesn't kill, vital organ tissue disruption does...).

I've shot full milk jugs with a 35 grain V-Max in a k-hornet at ~3300+ fps and 170,000 rpm. I don't know if that's past the rotational strength of the core, but it seems like it is as nothing makes it to the back face of the jug to make a mark. Instead, the jug top is launched about 15 yards up into the air, and the jug is split open and flattened pretty impressively, with a nice round hole in the plastic on the front face if you put it back together, and no marks on the pristine back. It may not meet the definition of "explosive" and it may not be directly due to rotational energy, but it is true that the rate of energy transfer to a target greatly increases when the core is overstressed beyond it's mechanical limit. It certainly looks "explosive." :)


OK, just having fun now... :popcorn:
Let's see, 1625 joules of translational, and TNT is generally considered to have 4184 joules of explosive energy per gram, so that means you've got about as much energy in a 224 at 3000 as 6 grains of TNT.

Even if you assume the majority of the energy from a bullet is released into the target over three inches, that gives an energy release period of more than about 100 microseconds, whereas (theoretically) detonation of 6 grains of TNT would release it's energy in around 1 microseconds. "Explosive" energy release in a p-dog would happen over a much longer time than if it were actually explosive... however, since we can only see things occurring at a rate of tens of milliseconds, we're not going to be able to tell a difference in terms of rates from looking at a p-dog hit by a disintegrating bullet vs. actually blown up! Unless of course, it's overkill caddy-shack style. :) Ahhh... I love that movie.

http://youtu.be/R5yCwN7wymc

OK, done doodling. :)

Best regards,
DrB

[DrB]

I see where you and gear are going, leftiye, I think.

I've been thinking along similar but different lines. I thought we should be calculating bullet metal stresses from different loading mechanisms: rifling torque, centripetal acceleration, and linear acceleration/base pressure (maybe some others I haven't thought of). Then we could look at some empirical data sets with as much equal as possible (not changing too many variables at once) and try to say what matched best in terms of the shape. For example, I'd expect angular acceleration limits to be strongly affected by caliber, whereas linear acceleration limits shouldn't be -- seeing the direction and magnitude of change in RPM values from one caliber to the next at incipient failure might tell you if it was angular velocity or acceleration vs. linear acceleration. Superposition of loads would cause material failure before any of the limits alone, but looking at them together might let us start matching up general trends as to how things were behaving, and better understand how things like paper-patching were enabling higher velocities/rpms.

I don't know that friction is the right way to look at this... but then I don't know much at all about tribology, or how it relates to shootin' cast bullets. Maybe you can get sufficient energy rates into the metal surface layers to melt it... I have no idea, but I also don't know how you would go about determining you even had metal on metal vs. metal on film (gas or lube) on metal.

Also, we already think we know that group dispersion at close range due to small bullet imbalance should be pretty constant with velocity for pre-existing damage. So if you see groups opening up with hotter loads, presumably it is because you have started causing damage to the bullet. Either bullet imbalance or gas venting at barrel exit could be causing those lateral velocities, though...

Best regards,
DrB

[geargnasher]

Now we're getting somewhere. Thanks to DrB for the brainpower. My intent isn't to derail the thread, but it seems to me at least that the practical reason for applying some basic math and physics to internal ballistics as it relates to lead boolit stresses is to increase understanding of the factors involved with the accuracy/velocity limitations we experience. This is one area I don't understand very well since it's impossible to be in the barrel with the boolit when it's fired, and the evidence from recovered projectiles doesn't tell us the whole story.

I like the term "rifling torque" to describe the stresses the boolit encounters as it's being "spun up" in the barrel. Rifling torque is what causes skidding (triangular engraving patterns) on revolver boolits that have a long jump to the rifling and sudden, high-speed jerk into a rotating motion by the lands. I'm not sure that the boolit surface engagin the sides of the lands gets hot enough to actually melt due to friction, or what effect any damage done to the engraves really has, but it seems to me that several things contribute to inaccuracy that involve velocity/acceleration and twist rate once a certain point is reached, and I'd like to know more about it.

Take a .30 caliber rifle as a common example. We know that our ultimate accurate muzzle velocity will have a certain limit with any given setup. We know that using faster powders will lower the accurate velocity. We know that slower powders will raise it. We know that harder boolits will raise it. We know that slower twist rate will raise it. We know that a boolit that fits the throat and is supported well, combined with a chamber neck and case neck fitting closely will raise it higher than a poor fit. We know that Loverin-style boolits with short, round noses generally shoot better than other designs at any velocity. We know that lousy muzzle crowns ruin accuracy. We know that compacting fillers like bran and BPI Original can raise accurate velocity potential in some cartriges, but not others. We know that lube can ruin accuracy for several reasons, but I haven't found that spinning off chunks unevenly is an explanation for this particular velocity/accuracy issue, so I discount balance in flight as the main culprit. We know that unbalanced boolits don't shoot well, but I remain unconvinced that imbalance is the primary cause of the velocity/accuray limit that Larry Gibson describes as the "rpm threshold". What we don't know for certain is how all these things fit together, but I see trends revolving around the common factor of boolit/land interaction. I maintain that twist rate and accurate muzzle velocity windows are related closely, but that the cause is a tangent departure from the muzzle due to damage during launch, NOT an issue with balance in flight.

If it were balance issues, the paper patch wouldn't help that much. Paper cannot support a boolit nose where it doesn't touch the bore, patched boolits have bare bases with no gas check to support them, the paper has no power to prevent the "accordion" effect on lube grooves, and the bore supports the remainder, so there is no logical explanation for why they shoot better, yet THEY DO. Patched boolit performance, with only rudimentary loading techiques and often with severely swaged or inferior castings can and frequently do shoot 25% or more faster with the same accuracy and alloy as an unpatched boolit. The only explanation I have is that the patch improves the boolit/land interaction somehow, either reducing friction, adding reinforcement to the boolit metal, or preventing damage so that the boolit will exit the muzzle crown squarely (I assume). For whatever reason the patch fixes the normal accuracy/velocity limit, and I want to know why so I can focus on duplicating the beneficial effect in normal production twist rates without the patch. I have been able to achieve above-average, consistent success in the past with accurate, high-velocity work, but never the kind of performance associated with copper or paper jacketed projectiles.

Some would argue that "non-linear group dispersion" is proof of imbalance due to damage during launch (or before) being the culprit, but I think it's aerodynamic forces (acting in a number of different ways) compounding that cause it, primarily tipping at muzzle exit.

The bottom line is I think the problem with achieving accurate, high-velocity performance with regular boolits involves rifling torque and muzzle exit, NOT imbalance and wild helical pattens AFTER muzzle exit. I don't have any theories on exactly how rifling torque affects our HV accuracy, but I believe it is the primary factor, not spinning the boolit too fast per se.

Maybe some theoretical model can be assembled using some of the math DrB has developed, together with extensions such as I've indicated necessary in my post above, which will shed some light on specific failure points. If accuracy degradation can be linked directly to pressure on the engraves and what we do to counteract that pressure then we will have a USEFUL model for predetermining accurate limits before heading to the range, and a good explanation for when things begin to fail. This is my whole reason for being in these discussions.

Gear

[rbertalotto]

I always wondered about this...........

A few years ago I had two 6mm Remington Ackley rifles in a Prairie Dog town for a few days. One had a 1-8 twist barrel and the other a 1-14 twist. Both rifles were shooting identical loads with 55g , 6mm bullets.

I shot dozens of PDs at various distyances, from a few meters to hundreds of yards.

In every hit, it was VERY obvious that the 1-8 twist barrel was MUCH more explosive.........

I have no idea why, but I thought it had to do with roptational energy.

Bullets were traveling at nearly 4000 fps

[DrB]

I've got to get the equation for the stress field... I might suspect that the core becoming progressively more overstressed when you spin it faster affects the particle size distribution you get during break up and explain the rate of translational energy dump.

There really isn't enough rotational energy to directly cause much effect, IMHO. It has to be that the role of the RPMs is to overstress the core and cause very rapid deposition of the translational energy of the bullet.

For your cases, the numbers work out to:
1:8 Rotational energy is 0.46% of translational
1:14 Rotational energy is 0.15% of translational

Note that while the rotational energy in the 1:8 is three times higher than the 1:14 it is still tiny (less than two orders of magnitude smaller) compared to translational energy.

The higher the rotational stress in the bullet metal, the less likely that bullet fragments will be large enough to exit the target and carry energy away... whereas the actual rotational energy involved is quite small.

Best regards,
DrB

[williamwaco]

Don't know that many folks will care, but a member asked what the ratio between rotational and translational kinetic energies are for a bullet.

DrB

I remember the request and also remember doing the exact same study in 1961 while in school working on a bachelors in mathematics. At that time the Keith/Weatherby debate was in full swing.

There were two camps, the big bullets for big game (Keith) vs the light weight high velocity bullet fans of the "modern high velocity cartridges" (Weatherby/Ackley).

A good friend of my father's and mine, was a popular gun writer and a member of the high velocity team. He was constantly touting the massive increase in killing power contributed to the "large rotational component of energy" which added to the kinetic energy of the bullet. It was obvious that this rotation would cause tissues and fluids to be thrown violently outward from the bullet path.

I told him one day in a visit, that he needed to quit touting that rotational energy. It was not enough to count. I had not calculated it at the time but I knew it was very small. I told him I didn't care about everyone else in the debate but that sooner or later, someone was going to calculate the actual value and I didn't want him making a fool of himself.

I calculated it for him for a couple of the Weatherby hot rods. ( With my trusty bamboo slide rule. ) He didn't belive me since it was "obvious that with that extremly high RPM number the rotational energy just had to be huge.", and after all, I was just a 20 year old kid.

I noticed however that any reference to rotational energy dissapeard immediately from his writings.

Several years later, his wife told me that after I told him to quit talking about it, he called the local high school science teacher who verified my numbers.


WOW, isn't this a great hobby!






The phrases "rotational energy", "hydrostastic shock"

[DrB]

Gear, I'd caution anyone against focusing on any one mechanism exclusively. Seems likely (certain?) to me there are different constraints in play in different situations. That said, you've made an interesting summary of observations... interesting ideas there.

I am really interested in the PP thing, as that seems potentially revealing about the (partial) nature of the problem.

t may well be that the paper "softens" the stress impinged on the bullet metal by the rifling land drive surface. Instead of cutting the bullet metal and pushing it directly with the relatively narrow engraved drive surface, the rifling acts on the paper fibers which in turn spread the load onto the bullet surface, imparting it over a greater area of the surface through shear. It might be very interesting to look at a fired and unfired paper patched bullet surface under a microscope, as well as the patch material, and see what impressions were transferred and what the shapes are. I actually feel pretty confident suggesting this is at least one of the major things paperpatching does, is relieve rifling drive loads by spreading them over a wider area of the bullet surface. The one big question mark in my mind is what any cutting of the patch by the rifling may do in terms of limiting the ability of the paper to transfer loads through shear. Maybe 303guy could do a post-mortem on a PP bullet for which the patch didn't shred and stayed attached? If you could recover one reasonably intact and slit it off, it would be interesting to see if it still had an ability to handle a tensile load across the rifling marks. I have no idea if that could be done... might have a better chance though with a radically reduced load, like with trail boss or bullseye or such.

It may also act as a fiber seal against hot gas... gas cutting and velocity limits may be more closely related than we think.

Lastly, remember that bullet imbalance will cause an asymmetric load on the bullet which will increase pressure on one side of the bullet and decrease it on the other, and increases as the square of rotational rate. It may be that at sufficient RPM lube pumping mechanisms break down on one side or the other and gas cutting/bullet damage/asymmetric venting at departure occur. The asymmetric force is given by m * r * (rotational rate)^2. For a 100 grain bullet fired at 3000 fps out of a 1:10 twist barrel and a .001" cg offset, the stress in the bullet comes to about 19 pounds. If the available contact area in the bore to take react it out is about .1 square inches, then that results in about 200 psi of force. The stress increases proportionally with mass, and cg offset, inversely with barrel contact area, and as the square of rotation rate. Doesn't seem to me like this force is of sufficient magnitude to be causing us problems, but add it to the list.

There are also two different in flight RPM related phenomenon I haven't mentioned yet... I have not done my homework in terms of identifying whether they could/should be active in the physical regimes we are dealing with with cast bullets. While they absolutely occur for spin stabilized bodies in some situations, I'd hate to introduce a couple of new myths into everyone's thinking if they aren't physically relevant.

Anyway, those are my thoughts...

Best regards,
DrB



Now we're getting somewhere. Thanks to DrB for the brainpower. My intent isn't to derail the thread, but it seems to me at least that the practical reason for applying some basic math and physics to internal ballistics as it relates to lead boolit stresses is to increase understanding of the factors involved with the accuracy/velocity limitations we experience. This is one area I don't understand very well since it's impossible to be in the barrel with the boolit when it's fired, and the evidence from recovered projectiles doesn't tell us the whole story.

I like the term "rifling torque" to describe the stresses the boolit encounters as it's being "spun up" in the barrel. Rifling torque is what causes skidding (triangular engraving patterns) on revolver boolits that have a long jump to the rifling and sudden, high-speed jerk into a rotating motion by the lands. I'm not sure that the boolit surface engagin the sides of the lands gets hot enough to actually melt due to friction, or what effect any damage done to the engraves really has, but it seems to me that several things contribute to inaccuracy that involve velocity/acceleration and twist rate once a certain point is reached, and I'd like to know more about it.

Take a .30 caliber rifle as a common example. We know that our ultimate accurate muzzle velocity will have a certain limit with any given setup. We know that using faster powders will lower the accurate velocity. We know that slower powders will raise it. We know that harder boolits will raise it. We know that slower twist rate will raise it. We know that a boolit that fits the throat and is supported well, combined with a chamber neck and case neck fitting closely will raise it higher than a poor fit. We know that Loverin-style boolits with short, round noses generally shoot better than other designs at any velocity. We know that lousy muzzle crowns ruin accuracy. We know that compacting fillers like bran and BPI Original can raise accurate velocity potential in some cartriges, but not others. We know that lube can ruin accuracy for several reasons, but I haven't found that spinning off chunks unevenly is an explanation for this particular velocity/accuracy issue, so I discount balance in flight as the main culprit. We know that unbalanced boolits don't shoot well, but I remain unconvinced that imbalance is the primary cause of the velocity/accuray limit that Larry Gibson describes as the "rpm threshold". What we don't know for certain is how all these things fit together, but I see trends revolving around the common factor of boolit/land interaction. I maintain that twist rate and accurate muzzle velocity windows are related closely, but that the cause is a tangent departure from the muzzle due to damage during launch, NOT an issue with balance in flight.

If it were balance issues, the paper patch wouldn't help that much. Paper cannot support a boolit nose where it doesn't touch the bore, patched boolits have bare bases with no gas check to support them, the paper has no power to prevent the "accordion" effect on lube grooves, and the bore supports the remainder, so there is no logical explanation for why they shoot better, yet THEY DO. Patched boolit performance, with only rudimentary loading techiques and often with severely swaged or inferior castings can and frequently do shoot 25% or more faster with the same accuracy and alloy as an unpatched boolit. The only explanation I have is that the patch improves the boolit/land interaction somehow, either reducing friction, adding reinforcement to the boolit metal, or preventing damage so that the boolit will exit the muzzle crown squarely (I assume). For whatever reason the patch fixes the normal accuracy/velocity limit, and I want to know why so I can focus on duplicating the beneficial effect in normal production twist rates without the patch. I have been able to achieve above-average, consistent success in the past with accurate, high-velocity work, but never the kind of performance associated with copper or paper jacketed projectiles.

Some would argue that "non-linear group dispersion" is proof of imbalance due to damage during launch (or before) being the culprit, but I think it's aerodynamic forces (acting in a number of different ways) compounding that cause it, primarily tipping at muzzle exit.

The bottom line is I think the problem with achieving accurate, high-velocity performance with regular boolits involves rifling torque and muzzle exit, NOT imbalance and wild helical pattens AFTER muzzle exit. I don't have any theories on exactly how rifling torque affects our HV accuracy, but I believe it is the primary factor, not spinning the boolit too fast per se.

Maybe some theoretical model can be assembled using some of the math DrB has developed, together with extensions such as I've indicated necessary in my post above, which will shed some light on specific failure points. If accuracy degradation can be linked directly to pressure on the engraves and what we do to counteract that pressure then we will have a USEFUL model for predetermining accurate limits before heading to the range, and a good explanation for when things begin to fail. This is my whole reason for being in these discussions.

Gear

[garym1a2]

A bullet travel at 3300fps out of a 1:7 inch barrellel will spin less than one revolution in a milk jug. I think the 3300fps of the equation is what blows the jug, not the one spin.



Well, I don't know about debunking "explosive effect..." :-? that depends on what folks are trying to mean when they say that. All I would say is that liquefying prairie dogs isn't happening directly from the rotational energy. Folks with experience have told me that you can turn a prairie dog into little bitty pieces and soup... I believe them given what I've seen in bigger animals, and p-dog shoot videos.

What I would say is that spinning a bullet faster than the rotational rate that exceeds the strength of the core means that when the jacket ruptures on impact the core turns into an expanding cloud of lead particles. The small particles, because of their high drag to mass ratio, dump their translational energy into the target over a much shorter distance than the intact bullet would. The same bullet if it didn't disintegrate due to RPM might zip right through the target and carry much of it's energy downrange (not necessarily a bad thing, especially on a larger animal -- energy doesn't kill, vital organ tissue disruption does...).

I've shot full milk jugs with a 35 grain V-Max in a k-hornet at ~3300+ fps and 170,000 rpm. I don't know if that's past the rotational strength of the core, but it seems like it is as nothing makes it to the back face of the jug to make a mark. Instead, the jug top is launched about 15 yards up into the air, and the jug is split open and flattened pretty impressively, with a nice round hole in the plastic on the front face if you put it back together, and no marks on the pristine back. It may not meet the definition of "explosive" and it may not be directly due to rotational energy, but it is true that the rate of energy transfer to a target greatly increases when the core is overstressed beyond it's mechanical limit. It certainly looks "explosive." :)


OK, just having fun now... :popcorn:
Let's see, 1625 joules of translational, and TNT is generally considered to have 4184 joules of explosive energy per gram, so that means you've got about as much energy in a 224 at 3000 as 6 grains of TNT.

Even if you assume the majority of the energy from a bullet is released into the target over three inches, that gives an energy release period of more than about 100 microseconds, whereas (theoretically) detonation of 6 grains of TNT would release it's energy in around 1 microseconds. "Explosive" energy release in a p-dog would happen over a much longer time than if it were actually explosive... however, since we can only see things occurring at a rate of tens of milliseconds, we're not going to be able to tell a difference in terms of rates from looking at a p-dog hit by a disintegrating bullet vs. actually blown up! Unless of course, it's overkill caddy-shack style. :) Ahhh... I love that movie.

http://youtu.be/R5yCwN7wymc

OK, done doodling. :)

Best regards,
DrB

[DrB]

Ha! :) Neat story. :)

Yep, ballistics is an old science. On one of the prior threads I suggested spaced witness plates to record bullet motion in flight, and the very next post someone referenced a test one hundred years ago by Mann that did the EXACT same thing (and incidentally with a demonstration of the same lateral throw of an imbalanced bullet from the muzzle I'd just done a calculation on).

It seems clear to me that there is a huge volume of "lost art." Some really really sharp folks have no doubt discussed and analyzed in detail much of what we are discussing today, and somewhere out there in the literature many of the answers to our questions no doubt are already held.

Good ideas are timeless... I find it just as interesting that bad ideas are as well (but they are periodic). In engineering, bad ideas come back every five years, and REALLY bad ideas every 15. :)

Best regards,
DrB


I remember the request and also remember doing the exact same study in 1961 while in school working on a bachelors in mathematics. At that time the Keith/Weatherby debate was in full swing.

There were two camps, the big bullets for big game (Keith) vs the light weight high velocity bullet fans of the "modern high velocity cartridges" (Weatherby/Ackley).

A good friend of my father's and mine, was a popular gun writer and a member of the high velocity team. He was constantly touting the massive increase in killing power contributed to the "large rotational component of energy" which added to the kinetic energy of the bullet. It was obvious that this rotation would cause tissues and fluids to be thrown violently outward from the bullet path.

I told him one day in a visit, that he needed to quit touting that rotational energy. It was not enough to count. I had not calculated it at the time but I knew it was very small. I told him I didn't care about everyone else in the debate but that sooner or later, someone was going to calculate the actual value and I didn't want him making a fool of himself.

I calculated it for him for a couple of the Weatherby hot rods. ( With my trusty bamboo slide rule. ) He didn't belive me since it was "obvious that with that extremly high RPM number the rotational energy just had to be huge.", and after all, I was just a 20 year old kid.

I noticed however that any reference to rotational energy dissapeard immediately from his writings.

Several years later, his wife told me that after I told him to quit talking about it, he called the local high school science teacher who verified my numbers.


WOW, isn't this a great hobby!






The phrases "rotational energy", "hydrostastic shock"

[DrB]

A bullet travel at 3300fps out of a 1:7 inch barrellel will spin less than one revolution in a milk jug. I think the 3300fps of the equation is what blows the jug, not the one spin.

I think we are agreeing, but am not sure.

RPM does very significantly effect the stress in the bullet metal... this has been computationally and analytically demonstrated (I've seen the computational results, linked below if you have an interest, I plan on digging up and replicating the analytical results). Again, the role of RPM isn't to contribute much to the energy transfer to the target directly, but by causing the violent fragmentation of the bullet metal into particle size that rapidly slow down in the target and deposit the translational energy in a much shorter distance than a bullet would otherwise. The only thing holding together the soft lead bullet metal at very high RPMs is the jacket metal, which holds everything together (and ends up highly stressed). When it fails, the bullet core dissembles.

Here's a link to Varmint Al's excellent web page where he has done engineering analysis on several jacketed bullet designs. The jackets on these types of bullets are designed to withstand the stress due to centripetal acceleration of the core, but fail on impact.

http://varmintal.com/aengr.htm

That's not to say that the momentum transfer from an intact bullet can't explode a milk jug -- just that the momentum transfer can be much greater (complete, in fact) and more rapid if the bullet disintegrates on target due to RPM.

Best regards,
DrB

[BAGTIC]

I also am interested in the energy (including friction) expended during travel in the barrel to spin the boolit expressed as a ratio as you've done for the resulting rpm/velocity. I have no axe to grind here, it is acceptable that it be negligible.

During some previous discussions on another thread, I had thoughts that are as Geargnasher said - that the bearing faces of the lands, and the boolit might be encountering enough friction to soften or even melt. Most (if not all) of the force to rotate the boolit would be taken on those surfaces which are probly less than .004" wide in most instances. The issues that relate to deformation of the boolit in the barrel have long seemed to me to parallel the symptoms of a weak and or soft metal.

I doubt it. The bullet will be as engraved as it is going to get in the first bullet length of travel. After that the bullet has already conformed to the rifling and the main load will be the pressure caused by the gradually accelerating velocity.
If that pressure isn't enough to strip the bullet I doubt it would be great enough or enduring enough to heat the bullet much more. After the first few inches chamber pressure actually begins to drop and with it bore gas temperatures.

[303Guy]

... in a p-dog would happen over a much longer time than if it were actually explosive... however, since we can only see things occurring at a rate of tens of milliseconds, we're not going to be able to tell a difference in terms of rates from looking at a p-dog hit by a disintegrating bullet vs. actually blown up! I suspect the p-dog won't be able to tell the difference either!:mrgreen:

Thanks for the thought provoking insight DrB. This is an interesting thread! So much being said in such a short space.

On the cast boolit surface 'liquifying' under excess stress in the bore; that makes a lot of sense. Lead goes plastic under stress. We also know that ice melts momentarily under stress as caused by ice skates - it's what makes ice skating is possible. (Not the same thing though).


... detonation of 6 grains of TNT would release it's energy in around 1 microseconds. "Explosive" energy release in a p-dog would happen over a much longer time ...Now we are talking about brisance. ("Brisance is the shattering capability of an explosive. It is a measure of the rapidity with which an explosive develops its maximum pressure. "... not the power of a primer).

Anyway, I'll get back to reading the rest of the thread.:-)

[DrB]

Had a great email from a very thoughtful fellow still wondering if the RPM isn't more important to terminal damage than I am saying. I'm not certain I've fully understood the context of his question but I've tried to outline it below in case it is helpful to anyone else thinking about this:

So as I understand it, he has shot some fast twist FMJ .224s at high velocity and had very spectacular explosive effect on varmint, even out to ranges where he knows the velocity has enormously dropped off. I believe he's saying he finds it difficult to believe the RPM doesn't contribute more damage than I suggest, as it somehow contributes more resistance/force to the tissue in passage.

If I've gotten the above wrong, my apologies to him.

Here's what I'm saying, put a little differently:

If spun fast enough the bullet still behaves as though it is frangible regardless of how much velocity has decayed from the initial muzzle velocity as the rotation rate decays hardly at all... so even if the round slows down to say 1200 fps, you still have something that may tend to act like a glazer safety slug (rapid dump of energy into a sort of spherical cavity) -- if the jacket is stressed sufficiently to cause it to rupture on impact.

In the case of a fragmenting bullet, there just really isn't much energy at all in rotation to contribute to the impact event directly. To illustrate this, consider that my 22 spring piston air rifle firing a 17 grain 22 caliber pellet at 850 fps has MUCH more energy (36 Joules!) than a .224 60 grain bullet launched at 4000 fps from a 1:7 twist barrel has rotational energy (about 15 Joules). Either pales in comparison to the 2900 Joules at the muzzle of the .224 or 600 Joules at under 2000 fps downrange.

Just to be clear -- I'm not saying a highly spun bullet won't do massive damage on a small target (more than a less spun bullet with the same translational energy) or that the bullets won't disintegrate and make a skin full of mush... and I'm not saying that spin isn't critical in making it happen. I'm just saying the role of the spin is in preloading the bullet so it disintegrates on impact and causes rapid dump of energy to the target.

Best regards,
DrB

[leftiye]

Bagtic Maybe so, maybe not. I wasn't actually looking for complete melt, nor stripping, nor gas cutting. Most of what you said is exactly how I see it. I'm thinking that since gas seal depends on perfectly tight fit, that invisible to the eye amounts of displacement may be occurring and creating the phenomena that we don't seem to nail down in this quest. Granted , engraving the rifling takes only an inch or so (IDEALLY) but the heat generated has nowhere to go. And doubtless, more heat is generated as the rotation is accelerated, and the driving edges of the rifling and boolit continue to rub and cause friction and therefore heat. Lead isn't highly heat conductive, the heat doesn't have time to soak into the bullet. Only the first layer of lead atoms/alloy molecules may be getting heated and it won't dissipate very deeply into the boolit. Boolits that are touched instantly after being shot are very hot to the touch. All of that heat was originally confined to the skin of the bullet (which was therefore many times hotter).

[DrB]

Now we are talking about brisance. ("Brisance is the shattering capability of an explosive. It is a measure of the rapidity with which an explosive develops its maximum pressure. "... not the power of a primer).

:) Eh... well, kind of close to brisance, I guess...

Not that the p-dog would notice. :)

Did you get to the part where I suggested we volunteer you for a paper patched fact finding mission? :D

[Bret4207]

I don't have the math for any of this but I do have some thoughts-

The milk jug- when the bullet hits the jug it's two solids impacting. The fluid has no place to go except out. What RPM energy has to do with it I don't know, but an expanding bullet or flat nosed boolit are going to act differently than a spire point FMJ. It's the shock wave/hydraulic pressure doing the job, not RPM. The faster you drive a wedge into a block of wood the further apart the pieces fly. And they fly away from the wedge, just as the sides split away before the back of the jug. Isn't that simple energy transfer? That jacketed bullet is coming apart because it's meeting a solid object more or less, liquid don;t compress. The energy has to go somewhere.

The paper patch- someone mentioned the PP not supporting the lube grooves. I would rethink that. Any PP I've seen has shown that the patch enters/compresses into the grooves and that would be supporting them. That patch may well be acting as more of jacket than we think.

Lead alloys melting in the barrel- Leftiye followed up on his original thought with the time factor. I agree that time is the key. I don't believe there is enough time for the energy to transfer into heat and melt the boolit. Some of the heat felt in freshly shot projectiles is air friction, it's not just he barrel. Paper patches fired with smokeless never show burning or scorching that I've seen. BP will scorch a cloth patch sometimes though. Wonder why?

[rbertalotto]

A bullet travel at 3300fps out of a 1:7 inch barrellel will spin less than one revolution in a milk jug.

The "target" will slow the bullets forward travel and might even stop it, but the bullet is still spinning at a tremendous rate. yes?

[44man]

Side stepping a little fellas!
Boolit jump to the rifling seems to play little part in skid or poor accuracy. I learned that with the 45-70 BFR and now after shooting the BFR .500 S&W with a 1 in 15" twist and the long cylinder, super accuracy and no detectable skid has removed that from my thinking.
If I remember, this boolit has to travel about 1-1/8" to the cone.
I used to believe that a boolit needed to be very close to the forcing cone.
Here is a recovered boolt shot at maximum velocity from the .500.

[felix]

Need to stay within the scope with Gear's post number 4 to answer the questions in mind. Jacket material is everything when accuracy is contemplated. Yes, indeed, the RATE of acceleration comes into play big time, and is reinforced by 44man's picture. The 8 twister over the 10 twister post shows how the jacket material has a dramatic effect at the target. Paper jackets are most accurate because they keep the rifling clean, keeping the acceleration more consistent between shots. ... felix

[DrB]

RE different constraints on bullets -- I think you need to look at what the physics say. My experience with other problems is that the only answer that is usually right is "it depends." Anything else RE a generalization and you (by which I really mean to say "I" :)) usually are just flat wrong.

Seems to me skid could be a factor if a bullet makes a long jump, but that is going to depend on factors like velocity at engraving, linear acceleration at engraving, twist rate, angular inertia vs. rifling drive area, bullet metal strength, etc.

Bret -- I agree with what you're saying, except that spun sufficiently a FMJ spire point may disintegrate on impact. Spun insufficiently, and it may tend to zip right through the target. Spun sufficiently, and it will fly apart almost like a pre-fragmented slug, dumping all the momentum in the target... it acts like a flat point, but even more so.

Rbertalotto -- yes, in general, there are some good youtube videos a gentleman named Joe sent me (you can see the rotation of the bullet, from the action of a expanded petal on a pistol bullet I believe on the cavity wall). Tumbling can change things, and if the bullet lays over about the major moment of inertia that will slow rpm (usually I believe they end up stable in a base-backwards orientation), and if the bullet disintegrates then it doesn't make much sense to talk about rpm.

[M-Tecs]

I don’t believe the rotational energies of a bullet directly transfer to the target. I do believe that the rotational energies in the bullet effects its rate of expansion and how the bullets energy is transferred to the target.

Using a prairie dog as a target if you shoot it with a 458 Winchester Mag. using a 500 grain solid you will see no “explosive” difference between an 8 twist barrel and a 16 twist barrel.

Take this same prairie dog and shoot it with a .223 with varmint bullets out of a 7 twist and a 12 twist barrel you will see that the 7 twist appears to be more “explosive”.

The additional rotational energies are allowing the bullet to expand quicker thus appearing more “explosive”.

[felix]

Excellent!! Is it because the jacket had been weakened more by the higher twist? Or, is it because of the energy xfer? Both as well as including radial and circumferential together? Maybe the doc can run the calcs with proper assumptions about skin strength with 7 and 12 twist barrels at 3K fps. So, how thin is the forward engraving copper on varmint bullets? ... felix

[Bret4207]

R
Bret -- I agree with what you're saying, except that spun sufficiently a FMJ spire point may disintegrate on impact. Spun insufficiently, and it may tend to zip right through the target. Spun sufficiently, and it will fly apart almost like a pre-fragmented slug, dumping all the momentum in the target... it acts like a flat point, but even more so.



Just how fast do you have to spin a common FMJ to get it to disintegrate on impact???!!! The FMJs I'm thinking of I've seen hit steel plate and they don't disintegrate! I must not be familiar with the the ones you are speaking of.

[44man]

Just how fast do you have to spin a common FMJ to get it to disintegrate on impact???!!! The FMJs I'm thinking of I've seen hit steel plate and they don't disintegrate! I must not be familiar with the the ones you are speaking of.
Quite different. The .220 Swift would blow up on a blade of grass but would bore a hole through 1/2" mild steel. Guys that I told not to, poked holes through my targets with a .223.

[DrB]

Bret, are you saying that after impact of a lead cored FMJ with plate steel at ~ 3500 fps you've got a deformed bullet laying there? I have never seen anything at all like that. I'm thinking 44man has got the handle on what you were saying?

If you mean that they make a small crater or even punch a hole, then I agree with 44man that they are quite different. The target doesn't let the bullet expand, instead they sort of flow against each other with the pressure actually turning the advancing portions of the bullet in an annular U-turn against the cavity walls and ejecting them back towards the shooter.

This is one of the reasons I can tell you from personal experience it's really not a good idea to shoot at a steel target at very high velocity at closer ranges. You can catch ejected fragments coming back at you, particularly when the shots get fast enough to leave a deeper steep walled crater. Lower velocities and softer bullets tend to spray outward radially at the target, and sometimes you see a disc of the base rebounding back towards you. As the velocity gets higher and a crater starts to form, more of the bullet gets sprayed back up range.

RE FMJs blowing up on soft targets, I've never played with this, but one gentleman said he had this effect with the vietnam era pulled military FMJs out of a 1:7 twist at 3100 fps or ~320,000 rpm.

Best regards,
DrB

[DrB]

Oh hey -- for folks wanting to characterize whether this is happening with a particular bullet/rpm/velocity, let me repeat something I mentioned in a different context -- "witness plates."

So the way you would use them for this is that at the target you would provide what folks would call a "striker plate" that provides some initial resistance to start jacket rupture if it's going to rupture. Then after this you can put multiple sheets of foil, paper, or sheetmetal to record the expansion of any fragments.

Since you are mostly going to be in free flight after the striker plate, you would estimate the angle from any fragments from the bullet as follows:

C = caliber
w = rotation rate (in rpm)
Vd = downrange velocity at the target
d = distance behind striker plate
D = max diameter of bullet debris on target at a given distance d behind the striker plate

Then the diameter of the bullet debris cone at a given distance from the striker plate should be, for the most part, something less than:

D = d*(C*w*Pi/360)/Vd

If the bullet is rotating fast enough such that when the striker plate starts the rupture of the jacket the core comes apart, then the above relation should hold fairly well as an approximate outer boundary for most of the impacts from bullet particles. I am considering the problem as though the jacket simple pops and releases the core metal, with the outermost core flying outwards at no faster than it's tangential velocity at jacket rupture (it should be less due to the energy required for the particles to tear away from the main core).

If you are getting RPM induced fragmentation you would expect to see a shotgun pattern-like circle of perforation (except there would be a largish particle size variation, probably with some large fragments in the middle of the pattern) behind the striker plate on the witness plates with the pattern widening fairly linearly with distance. Otherwise you'll pretty much see a single perforation from the intact bullet body in the witness plates behind the strike plate.

So for a .224 at 320,000 rpm at the muzzle, and 2500 fps down range, this comes out to about the following:
10" behind plate 2.5"
20" behind plate 5.0"

I think a number of different materials for the striker plate would be interesting to see what was required to start fragmentation at a given velocity/rpm. Besides velocity/rpm and striker it will depend on the bullet design.

Also, I should have mentioned that I would never expect this behavior to be exhibited by cast bullets, as the metal strength is relatively homogeneous throughout, such that if the core is overstressed by RPM, that means we are already shedding pieces of the bullet in flight (and probably had unbelievable leading before the boolit ever made it out the bore).

Best regards,
DrB

[Bret4207]

I'm talking surplus FMJ ammo. Shot quite a bit of it into a swinger and often find distorted bullets laying near the plate. They aren't doing 3500, more like 2800, but then they aren't 223's either. I think the jacket has a lot to do with how that would work.

I'm sure you can spin a light jacketed varmint bullet so fast it'll fly apart, but with a heavier the jacket....in practical terms can we really spin, say, a 150 gr 30 call bullet with a heavy jacket fast enough to have that happen with any production gun? Seems unlikely.

[44man]

Good targets are made of armor plate and swinging them helps save the steel.
Mine are cheap, cut out of plain steel so I need to swing them. I can tell you that revolver impact has sheared aircraft bolts I use to hold the chains together.
My ram was beat into a salad bowl at 200 meters from just the .44. I beat the devil out of it with a sledge and could not even start to flatten it so I had to shoot the other side.
All targets at shoots are taken in and locked up because even with armor plate, rifle shooters would damage them. I have seen holes shot through 50# rams, 1/2" armor plate. Welds break and the feet fall off.
The wrong bullets that came apart fast would not knock all the rams over, there must be a slight dwell time on the steel so the bullet pushes. We called it "momentum."
A bullet spun less had more knock down.

[Bob Krack]

I thought we should be calculating bullet metal stresses from different loading mechanisms: rifling torque, centripetal acceleration, and linear acceleration/base pressure (maybe some others I haven't thought of). Don't mean to leave the subject and am not trying to at all but the actual terms "centripetal" and "centrifugal" have always confused me is as much as I kinda thought one was cause and the other was effect.

Could you supply a short "lay" definition of them?

Thank you kind sir,

Bob

[geargnasher]

Bob, Google is your friend. If you want the long version, pm me or DrB.

Gear

[geargnasher]

Need to stay within the scope with Gear's post number 4 to answer the questions in mind. Jacket material is everything when accuracy is contemplated. Yes, indeed, the RATE of acceleration comes into play big time, and is reinforced by 44man's picture. The 8 twister over the 10 twister post shows how the jacket material has a dramatic effect at the target. Paper jackets are most accurate because they keep the rifling clean, keeping the acceleration more consistent between shots. ... felix

I was throwing out the land pressure subject as a pertinent application of the questions posed by the OP, I don't think that exceeding the elastic limit of the boolit metal by spinning it too fast is really something seen very often in normal ranges of boolit stress. Yes, it happens, like in .22 caliber at 4k fps and weak bullet jackets, but I'm thinking other things go to pot with cast boolits long before they fly apart at the muzzle.

Now, here's some more food for thought: What if a boolit exits the muzzle with enough inertial force that it DISTORTS, rather than explodes? Since the compressive yield strength of lead is similar to it's tensile strength, a BH number could be converted to joules and run through DrB's formula to determine the point at which a boolit would begin to change shape once leaving the confines of the barrel. Could THIS be the "RPM threshold" of accuracy so commonly observed?

Gear

[felix]

Yes, that for sure will define the IDEAL range of Larry's threshold values. ... felix

[DrB]

I'm talking surplus FMJ ammo. Shot quite a bit of it into a swinger and often find distorted bullets laying near the plate. They aren't doing 3500, more like 2800, but then they aren't 223's either. I think the jacket has a lot to do with how that would work.

I'm sure you can spin a light jacketed varmint bullet so fast it'll fly apart, but with a heavier the jacket....in practical terms can we really spin, say, a 150 gr 30 call bullet with a heavy jacket fast enough to have that happen with any production gun? Seems unlikely.

I've never heard of anyone doing it with 30 cal, Bret and FMJ. Typically, though, I don't think we shoot 30 cal as fast as 22 with typical weight bullets as the recoil is punishing and there isn't much application outside of long range target shooting (or sniping). Also, barrel length becomes less practical since a fixed number of caliber barrel will increase proportionally in length to the caliber of the gun.

The .223 FMJ in the anecdote I was talking about was milsurp... but again, I've not seen it with FMJ personally. I am slightly skeptical about it in .223... on the other hand, the fellow who related it to me was using a 1:7 twist at very high RPM... So that made me give it more credence.

Maybe a test with FMJ in 223 is in order... I don't have a 223 in that fast a twist barrel.

Best regards,
DrB

[DrB]

I was throwing out the land pressure subject as a pertinent application of the questions posed by the OP, I don't think that exceeding the elastic limit of the boolit metal by spinning it too fast is really something seen very often in normal ranges of boolit stress. Yes, it happens, like in .22 caliber at 4k fps and weak bullet jackets, but I'm thinking other things go to pot with cast boolits long before they fly apart at the muzzle.

Now, here's some more food for thought: What if a boolit exits the muzzle with enough inertial force that it DISTORTS, rather than explodes? Since the compressive yield strength of lead is similar to it's tensile strength, a BH number could be converted to joules and run through DrB's formula to determine the point at which a boolit would begin to change shape once leaving the confines of the barrel. Could THIS be the "RPM threshold" of accuracy so commonly observed?

Gear

Gear, I agree with you that RPM exceeding boolit stress is improbable, in part because stresses are generally additive and are going to be higher in the barrel than in free flight. I don't think you can "successfully" launch a relatively undamaged bullet at sufficient RPM to encounter the stress due to centripetal force limit. Launching them with a plastic sabot like Bullshop mentioned is probably the way to get closest to the true ultimate RPM limit due to centripetal acceleration.

This is one reason I think it would be interesting to calculate the RPM vs. material strength and caliber relation. Whatever other limitations there may be, we'll know that that is a boundary that can not be physically crossed. It's also pertinent to the current subject applied to jacketed bullets... it may well be that in most cases with "explosive" varmint bullets the limiting core stresses are not typically exceeded until the impact stresses are added, and then the combination of the impact stresses with the the rotational stresses cause disintegration.

I think you were on to something with regard to the land drive area stress. It could explain the reason why PP can be driven faster than plain cast lead with the same alloy. 303Guy has got some interesting new pictures that to me look like they may show that the paper patch is imprinted on the bullet surface, is relatively uncut by the rifling... maybe the PP is spreading those rifling loads over a much larger area of the bullet surface and enabling the higher velocities.

Best regards,
DrB

[DrB]

Don't mean to leave the subject and am not trying to at all but the actual terms "centripetal" and "centrifugal" have always confused me is as much as I kinda thought one was cause and the other was effect.

Could you supply a short "lay" definition of them?

Thank you kind sir,

Bob

Bob, here's my best try... I hope it helps. :) (Gear is right that googling it may help you more, as you will likely find some helpful pictures, which are a better way to explain this than with just words.)

Say you are in a car going around a curve -- centripetal force would be the force acting on the car (through the tires) towards the center of the curve holding it to the radius of the curve. Centripetal acceleration would be the acceleration the car was experiencing, ie, acceleration towards a center of rotation (the center of the curve) such that it followed a curved path.

Centrifugal force -- if you are a passenger inside the car, "centrifugal" force is the force that you would perceive was pushing you against the side of the car on the outside of the curve. As Gear as suggested before, it's generally considered a fictional force as it's dependent on the frame of reference (it's an "inertial force" that's only observed in a non-inertial frame of reference). I had a dynamics professor once who threatened to give us a zero on any assignment or test in which we used it... I don't have much problem with it, but he sure did. :)

Best regards,
DrB

[Bret4207]

I've never heard of anyone doing it with 30 cal, Bret and FMJ. Typically, though, I don't think we shoot 30 cal as fast as 22 with typical weight bullets as the recoil is punishing and there isn't much application outside of long range target shooting (or sniping). Also, barrel length becomes less practical since a fixed number of caliber barrel will increase proportionally in length to the caliber of the gun.

The .223 FMJ in the anecdote I was talking about was milsurp... but again, I've not seen it with FMJ personally. I am slightly skeptical about it in .223... on the other hand, the fellow who related it to me was using a 1:7 twist at very high RPM... So that made me give it more credence.

Maybe a test with FMJ in 223 is in order... I don't have a 223 in that fast a twist barrel.

Best regards,
DrB

Well, my confusion and disbelief (if you can call it that) stemmed from me not even considering 223 in my thoughts. I guess when I think "FMJ" I think 30, 8mm, stuff like that. I still would think jacket thickness would be the controlling issue. Again, when I think of FMJ jackets I think of heavy 30, 311 and 8mm type stuff. Hard to believe that type of bullet could ever disintegrate from rotational forces without a hard surface impact to help.

[Bret4207]

Now, here's some more food for thought: What if a boolit exits the muzzle with enough inertial force that it DISTORTS, rather than explodes? Since the compressive yield strength of lead is similar to it's tensile strength, a BH number could be converted to joules and run through DrB's formula to determine the point at which a boolit would begin to change shape once leaving the confines of the barrel. Could THIS be the "RPM threshold" of accuracy so commonly observed?

Gear

I was more or less under the impression that was part of what Larry is talking about.

[geargnasher]

Bret, I agree to a point. The way I understand what Larry was saying is essentially that boolits aren't perfect to begin with, and get made even less perfect by launch stresses , and these imperfections cause the boolit to misbehave once free of the bore. He relates, by observation, a range RPM of the boolit to a tendency for groups to be the best, while exceeding that rpm range will usually cause "non-linear group dispersion", meaning that the farther the boolit travels, the proportion of group size increases at a much faster rate than a boolit withing the ideal rpm range he states.

I have observed the same trends, approximately, and don't disagree that some accuracy/velocity trend exists, but I don't believe that a direct relationship between "RPM" and the inaccuracy has been proven, nor do I believe that the reasons for the non-linear dispersion above the "threshold" are really very well understood. The reasons Larry gives for this non-linear dispersion don't hold water in my mind, and I'm interested in finding the true CAUSE of the "RPM threshold", and there's more to it than has been figured out so far.

In essence, I don't believe it is correct to assume that excessive RPM is the CAUSE of non-linear group dispersion when a boolit is fired "too fast" out of a barrel with "too fast" of a twist rate, I think it's something else, and I don't buy the concept that simple distortion and physical imbalance problems with the spinning boolit cause it to to "wongo" way down range, if that were so the RPM threshold would be more gradual and much broader. My beliefs are only that, and I'm open finding new ones as evidence and well-supported explanations come about.

Nobody has mentioned boolit damage occuring after the boolit is free of the gun, just wondered what y'all thought about that. I'm going to go have a gin&tonic and ponder some math, some study should tell whether it is even possible to exceed the boolit's yield point after muzzle exit.

Gear

[geargnasher]

Bob, here's my best try... I hope it helps. :) (Gear is right that googling it may help you more, as you will likely find some helpful pictures, which are a better way to explain this than with just words.)

Say you are in a car going around a curve -- centripetal force would be the force acting on the car (through the tires) towards the center of the curve holding it to the radius of the curve. Centripetal acceleration would be the acceleration the car was experiencing, ie, acceleration towards a center of rotation (the center of the curve) such that it followed a curved path.

Centrifugal force -- if you are a passenger inside the car, "centrifugal" force is the force that you would perceive was pushing you against the side of the car on the outside of the curve. As Gear as suggested before, it's generally considered a fictional force as it's dependent on the frame of reference (it's an "inertial force" that's only observed in a non-inertial frame of reference). I had a dynamics professor once who threatened to give us a zero on any assignment or test in which we used it... I don't have much problem with it, but he sure did. :)

Best regards,
DrB

I explained this a year or two ago in the context of boolit lube "spinning off" of the grooves at high-rpm. The topic involved hard vs. soft lubes and inaccuracy being caused by partial and uneven loss of lube downrange. Where the breakdown of understanding often occurs is trying to explain the "inertial frame of reference". It's easy enough for me to discard the concept of "centrifugal" force entirely in that example and focus on the fact that lube wants to travel in a straight line and is constantly being pulled into an arc until finally one force exceeds the other and it flings off on a tangent, but the observed effect of "centrifugal" force is still a valid way of conceptualizing what's going on for many people.

Gear

[geargnasher]

Ok, I think we can put boolit distortion due to "centrifugal" force to rest. A .30 caliber boolit at 16 BHN and 2K fps in a ten-twist barrel will experience less than 1/10th lb/ft of radial force due to the rotational velocity, whereas it would require almost 160 lb/ft of force to stretch the boolit.

Gear

[Larry Gibson]

Ok, I think we can put boolit distortion due to "centrifugal" force to rest. A .30 caliber boolit at 16 BHN and 2K fps in a ten-twist barrel will experience less than 1/10th lb/ft of radial force due to the rotational velocity, whereas it would require almost 160 lb/ft of force to stretch the boolit.

Gear

Then that begs the question; what do it be? Could be the "frame of reference" is the bullet in flight. The "fictional" enertial force doesn't cause any real problems with a train, truck or car going around a curve unless the speed is such that the "fictional" enertial force becomes great enough to cause the train, truck or car to leave the curve (those are called "roll overs" from taking the corner too fast BTW). Perhaps the train, truck or car then exceeded the "roll over" threshold:razz:

Larry Gibson

[DrB]

Gear, my calculation on the maximum stress was 307psi for your scenario of a 30 cal at 2000 fps in a 1:10 twist... double checking my work here. :) If you would, I'll forward you some additional info for you to check me on if you care to? It's been a while since I've done much stress analysis.

The above stress will occur on the centerline of the bullet, and idealizes the bullet as a solid cylinder.

Ultimate stress for soft lead is 1740 psi, yield around 800 psi at .2% elongation, I believe. So in this case we aren't close to ultimate, or yield. Edit: So I've found other references that suggest significantly higher ultimate stresses even for dead soft lead... haven't found a good reference yet. Apparently there's more emphasis on data for solder applications than tensile strength. Felix... Care to expand on what you know about strength properties? :)

For a .224 at 3500 fps from a 1:7 twist, I get about 1000 psi stress in free flight from centripetal acceleration... So if I've crunched my numbers right, in light of this, it seems to me that the role of spin in a varmint bullet is to pre stress the core and enhance fragmentation. Note that an expansion (mushrooming) of the tip to just a bit from 5.56 to cause the metal to fail from centripetal force alone. Also note that a number of varmint bullet designs I've seen have a core that is partially hollowed in the nose -- this will substantially increase the peak stress on the core centerline (as there is less material to handle the radial tension from the centripetal acceleration of the outer portions of the bullet). I expect that upon jacket rupture for one of these designs at high RPM, little stagnation pressure from the impacted tissue is needed to cause fragmentation.

If anyone has a good tabulation of lead yield/ultimate values as a function of alloy/condition they would like to share that would be appreciated.

Best regards,
DrB

[DrB]

I was more or less under the impression that was part of what Larry is talking about.

+1 Gear's 44.

Ironically, there is an RPM dependent free-flight phenomenon that may fit the data I've been looking into from an old job I used to do. It'll be interesting to see if the dynamics fit... Of course, that might be making way too much soup out of too little meat. A failure to correctly account for wind and muzzle velocity variations both also can account for a non linearly opening of group size at greater ranges, as can the order of shooting (shooting near shots starting cold and unfouled, and farther shots hot and fouled). It would be most convincing I reckon in terms of demonstrating a real non-linear enlargement of group size to have an uninvested person shoot alternating shots at four different targets down range (low rpm near, high rpm far, high rpm near, low rpm far). By distributing the shot order impacts such as wind and fouling could be minimized. Velocity SD & gravity would still have to be controlled for, however... but might not be significant depending on the range and magnitude of the expected effect. You measure velocities and calculate the effect on group size due to ballistics to ensure MV SDs aren't contributing significantly.

When talking about run of the mill accuracy problems with cast bullets IMHO folks should consider how much accuracy degradation is already attributable to lateral throw from the muzzle due to CG offset from the axis of rotation, as well as gas shove at crown departure due to bullet base damage/asymmetry. The former is easy to calculate and fairly easy to test. The later isn't difficult to calculate a rough magnitude on.

My opinion is that if we are talking about better understanding the base pressure/linear acceleration/angular acceleration/twistvelcoity/RPM limitations of accuracy for a cast bullet I really think we need to be considering the strength of materials more. Gear is IMHO on the right track. The prior rpm/stress calculation is a starting offering for me. I'll try to get the equation posted up with a chart if folks have an interest. Really, the way we'd visualize something like this in a multidisciplinary design problem is create a constraint map showing where the various boundaries are that result in (material) failure due to one constraint or another. It's complicated here somewhat because we may not be talking about gross failure, but just a little bit of failure that allows CG offset and base damage to occur... ultimately, getting the shapes of the constraints and comparing them to the shapes of the empirical data may be the best bet for getting at what constraints are making a difference.

[Bret4207]

The more I learn, the less I know...

[44man]

The more I learn, the less I know...
Me too! :smile: I envy those that think in math since I can only think about what I see or hold in my hand.
Some of this is like the "big bang", did the universe start from nothing? Or are we living on an electron in God's fishbowl?
I make a gun shoot within the parameters of it's and the bullets design. Math will not let me go beyond that.
While I understand much of this discussion I have to ask WHY?
It sounds like Greenhill where it can be proved to work by changing all the figures to make what you do "fit."
Yesterday the neighbor woman wanted to learn to rebuild the carbs on her lawn mowers. I had her wash one off and as I took it apart I explained each thing. Ran into a problem with a jet that needed drilled for an easy out, then the threads needed chased so I could put in the new one. I went through each step, put it on the engine and it started with the first spin. I set the needles.
Does anyone here expect her to do it herself? I don't. What did she learn? She learned how to wash the thing off!
She is where I am with guns. I turn the key and make it work. The engine would never run with the wrong parts and the gun will never shoot with the wrong parts.
Practical limits, never theory!

[felix]

If anyone has a good tabulation of lead yield/ultimate values as a function of alloy/condition. ... Doc

That is the MAJOR problem. ... felix

[DrB]

What determines the "practical limits"? Experience? Theory informed by experience? :) The efforts of folks who have gone before us, and written their experience and interpretation down for our benefit?

Re math, etc., hey, you use the tools you have (and are comfortable with, and enjoy using)...

I reload and cast in part because I enjoy learning and playing with loads to get a better understanding and better performance. Random trial and error can be expensive, and interpreting data as saying something it doesn't can have costly consequences. Theory does matter. For example, knowing the potential impact of weight variation among cast bullets on accuracy is a pretty practical thing to know... Is culling for x grains of variation in weight for this particular boolit weight and caliber a crazy waste of time? I sure would like to understand the what and why of boolit weight variations, and how it should extend to different calibers, twists, and bullet weights. :)

I'm interested in the experiences and observations of folks like you and Bret, and appreciate your passing them on because experience is an expensive way to learn... if reality doesn't match up to an idealized theory, theory has to change. :) Reality is. If y'all don't like or agree with any of the theorizing, I think that's great, especially if you think it disagrees with what your experience tells you and are willing to share what your own efforts taught you.

Speaking of which, time for some more testing.

Best regards,
DrB

[DrB]

If anyone has a good tabulation of lead yield/ultimate values as a function of alloy/condition. ... Doc

That is the MAJOR problem. ... felix

:smile: Well I didn't immediately find everything I was looking for, but with all the minimum wage goober grad students out there with ingstroms I gotta figure it has been measured six ways to sunday a dozen times. Just gotta find it. Lead is an important engineering material... Call me an optimist. :)

[45 2.1]

Since the compressive yield strength of lead is similar to it's tensile strength

Where did you come up with this assumption? Nothing could be further from the truth.



I have observed the same trends, approximately, and don't disagree that some accuracy/velocity trend exists, but I don't believe that a direct relationship between "RPM" and the inaccuracy has been proven, nor do I believe that the reasons for the non-linear dispersion above the "threshold" are really very well understood. The reasons Larry gives for this non-linear dispersion don't hold water in my mind, and I'm interested in finding the true CAUSE of the "RPM threshold", and there's more to it than has been figured out so far.

For the above statement in blue........ The cause has been figured out... and you have been told... several times now by several of us. All that remains is that you understand the concepts...... and NO, Larry isn't the author of the truth.

[leftiye]

Hey, no skipping stones. Waddle on in here and help out! And please don't keep any truth secret.

[303Guy]

Originally Posted by geargnasher http://castboolits.gunloads.com/images_acps/buttons/viewpost.gif (http://castboolits.gunloads.com/showthread.php?p=1368969#post1368969)
Since the compressive yield strength of lead is similar to it's tensile strength
Where did you come up with this assumption? Nothing could be further from the truth.Why would that be wrong? Lead is very ductile and it's tensile yield strength is quite similar to its compressive yield strength. The stuff just flows. It has an ultimate yield strength of a mere 12 MPa. I can't find the compressive yield strength figures anywhere I've looked so I could be wrong.

[geargnasher]

Why would that be wrong? Lead is very ductile and it's tensile yield strength is quite similar to its compressive yield strength. The stuff just flows. It has an ultimate yield strength of a mere 12 MPa. I can't find the compressive yield strength figures anywhere I've looked so I could be wrong.

For ultimate compressive yield strength refer to the brinell scale we use for lead alloy hardness, that's what it's measuring.

Bob, since you must have the ASM handbook collection handy, how about some figures on any common binary or ternary boolit alloy, or something close, like lead/tin babbit? Do you remember why Rockwell testing was invented?

Gear

[303Guy]

OK. The compressive and tensile strength of lead is indeed similar. However, in compressive mode, the boolit will be supported by the bore. Lateral pressure under compression due to gas pressure from the rear might be expected to increase the shear strength of the rifling engaging surface of the boolit. Placing a layer of paper between the boolit surface and the bore might increase that strength quite a bit more.

[303Guy]

Nobody has mentioned boolit damage occuring after the boolit is free of the gun, just wondered what y'all thought about that.Do you mean as in muzzle blast damaging the base edge of the boolit?

[45 2.1]

OK. The compressive and tensile strength of lead is indeed similar. However, in compressive mode, the boolit will be supported by the bore. Lateral pressure under compression due to gas pressure from the rear might be expected to increase the shear strength of the rifling engaging surface of the boolit. Placing a layer of paper between the boolit surface and the bore might increase that strength quite a bit more.

This is where knowledge has an upper hand. ANYONE who relates the tensile strength of a boolit to any application a boolit undergoes is completely missinformed. The boolit is under compression, not tension. Two completely different modes of loading there. Add to the fact that it is alloyed increases the difficulty in understanding of what occurs. For example: lets take the 50/50 ww/Pb alloy....air cooled its about 8 BHN and very malleable with that low antimony content it has.... water drop it and let it age harden its about 20 BHN and tough. Same alloy isn't it....... dependent on how you cool it it has two uses and hardnesses. BHN is not and indication of usefulness part of the time. Now just why do some folks loads fail at around 1600 fps................. PRESSURE which missalignes the boolit in the throat. Shoot an undersize boolit whether on band or nose that is ill fitting and results are predictable. That can be mitigated thru useing slow burners, properly fitted boolits and buffer. Check the pressure level of the accuracy loads in the older ( Lyman #45 manual) and see where most accuracy loads occur. Barrel harmonics goes hand in hand with those node points also.

[Bret4207]

Hang onto your hat 45 2.1- BINGO! What you posted lines up exactly with my thoughts on the whole Bhn game. So do the questions on leads strengths- what are they talking about? Lead, lead tin, or lead/tin/antimony? Or maybe lead/tin/antimony/copper/arsenic/zinc? What heat treatment or non-treatment is offered? Every one of those options can be the same or different. Merely saying "I'm shooting 15 Bhn boolits" tells you almost nothing.

Like I said, the more I learn the less I know.

[Larry Gibson]

Very good 45 2.1.

You gave a very good explanation of the difficulties maintaining bullet balance during casting, loading and shooting (pre launch, pre muzzle exit, etc.) during the internal ballistic phase based on different alloys, BHNs and the toughness of cast bullets. You give an excellent reason why the bullets become unbalanced during the internal ballisitics phase and before. But what then is the cause of inacuracy during flight (external ballistics) when we push velocities above those "accuracy loads in the older ( Lyman #45 manual)" now that you've explained the reason?

Larry Gibson

[Nrut]

Very good 45 2.1.

You gave a very good explanation of the difficulties maintaining bullet balance during casting, loading and shooting (pre launch, pre muzzle exit, etc.) during the internal ballistic phase based on different alloys, BHNs and the toughness of cast bullets. You give an excellent reason why the bullets become unbalanced during the internal ballisitics phase and before. But what then is the cause of inacuracy during flight (external ballistics) when we push velocities above those "accuracy loads in the older ( Lyman #45 manual)" now that you've explained the reason?

Larry Gibson
All in good time grasshopper..

[felix]

"Why's everybody always pickin' on me?" from Jerry Leiber's and Mike Stoller's song, "Charlie Brown", as sung by the Coasters. ... felix

[Nrut]

"Why's everybody always pickin' on me?" from Jerry Leiber's and Mike Stoller's song, "Charlie Brown", as sung by the Coasters. ... felix

[smilie=l:

[BAGTIC]

Bagtic Maybe so, maybe not. I wasn't actually looking for complete melt, nor stripping, nor gas cutting. Most of what you said is exactly how I see it. I'm thinking that since gas seal depends on perfectly tight fit, that invisible to the eye amounts of displacement may be occurring and creating the phenomena that we don't seem to nail down in this quest. Granted , engraving the rifling takes only an inch or so (IDEALLY) but the heat generated has nowhere to go. And doubtless, more heat is generated as the rotation is accelerated, and the driving edges of the rifling and boolit continue to rub and cause friction and therefore heat. Lead isn't highly heat conductive, the heat doesn't have time to soak into the bullet. Only the first layer of lead atoms/alloy molecules may be getting heated and it won't dissipate very deeply into the boolit. Boolits that are touched instantly after being shot are very hot to the touch. All of that heat was originally confined to the skin of the bullet (which was therefore many times hotter).

You are assuming that the heat in the bullet spread fom the outside in.

The example I like to use is to put a lead bullet in a vise. Drag the flame from a gas welding/brazing torch across the the base of the bullet as fast as you can. Look for signs of melting. You won't find any. It takes temperature AND exposure time to heat the bullet. The powder gases are hot enough if they were sustained long enough but they aren't. Most, not all, will agree that had alloys are less apt to smear than pure lead. Ironically pure lead has a higher melting point that many bullet alloys.

Most of the heat gained by the bullets is created by the physical deformation of the bullet caused by setback. That heat is created equally and throughout the bullet simultaneously. It does not depend on condustion to spread it.

[felix]

No, not really. Most of the heat obtained by the projectile is from the powder burn. ... felix

[Larry Gibson]

All in good time grasshopper..

Now ain't that the truth:drinks:

Larry Gibson

[geargnasher]

This is where knowledge has an upper hand. ANYONE who relates the tensile strength of a boolit to any application a boolit undergoes is completely missinformed. The topic of this thread involves rotational energy RPM, as in do bullets/boolits load up due to centripetal acceleration and then, at some point, "explode" either due to inertial jacket failure or impact with a target. I was postulating that a boolit might expand or deform due to centripetal acceleration alone upon muzzle exit, causing the boolit to expand in the body portion, possibly in an irregular fashion causing inaccuracy above a certain "RPM". Just a hairbrained idea, and I have done some figuring that I believe shows this point to be moot at normal cast boolit loading levels. The boolit is under compression, not tension. Not outside the barrel it isn't, see, that's what got me thinking. Air resistance acting on the nose might be compression, but centripetal acceleration acts on the boolit metal, and the boolit metal has to push BACK to keep from flying apart, so it is in tension outside of the barrel. You probably remember the formula off the top of your head, but if not do what I did and refer to any engineering texbook on how to figure rotational stresses of solid discs, cylinders, or open-centered tubes and discs to see the stresses on the metal, and in what direction, although probably not enough to matter. Two completely different modes of loading there. Of course, but the tensile and compressive strength properties of ductile metals are often similar. Add to the fact that it is alloyed increases the difficulty in understanding of what occurs. Indeed. But alloying and grain structure manipulation tend, I say tend, to affect the results of both methods of loading in similar ways. For example: lets take the 50/50 ww/Pb alloy....air cooled its about 8 BHN and very malleable with that low antimony content it has.... water drop it and let it age harden its about 20 BHN and tough. Same alloy isn't it....... dependent on how you cool it it has two uses and hardnesses. BHN is not and indication of usefulness part of the time. Again, grain structure affects strength of both compression and tension in similar ways as far as I understand it. Now just why do some folks loads fail at around 1600 fps................. PRESSURE which missalignes the boolit in the throat. No doubt. I never argued with the basics of sound loading techniques, but still there are limits fairly early on with the gas-checked, grease-groove boolit that make me think that's not all there is to it. Shoot an undersize boolit whether on band or nose that is ill fitting and results are predictable. That can be mitigated thru useing slow burners, properly fitted boolits and buffer. Ah. Buffer. It's amazing what buffer can do to increase useable velocity range in normal cast boolits. Almost makes a gas check superflous in some instances. So why is that? Keeping the base square at muzzle exit? Absorbing shock? Preventing gas-cutting during the transition into the rifling? All of the above?Check the pressure level of the accuracy loads in the older ( Lyman #45 manual) and see where most accuracy loads occur. I have. That's why I pointed out the factors of pressure and alloy strength in Larrys most recent RPM thread. I've also checked the "accuracy" loadss (never shot on paper, just loads that showed consistent internal ballistics) in Lyman #49, compared them to real life, and also to Lee's data, and found that consistent pressures don't always, or even often, relate to consistent accuracy, although alloy toughness has a lot to do with accuracy potential as velocity is increased. Barrel harmonics goes hand in hand with those node points also. Yes. But barrel harmonics affect all projectile types of a similar weight and shape in a similar way, but the accuracy point of a jacketed bullet might be well above the potential for its lead counterpart to velocity/pressure limitations. I'm interested in disecting these limitations more.

If a paper jacket is sufficient to overcome the vast majority of the limitations imposed on accuracy and velocity by traditional, grease-groove boolits, then it must not take very much at all to counteract the forces which ruin our groups. If that cause can be pinpointed, perhaps a simpler solution could be found which would give traditional GG boolits the same velocity accuracy potential as a PP boolit?

Gear

[Larry Gibson]

Gear

Assuming every cast bullet is a perfectly cast and balanced bullet that is correctly fitted to the throat and aligned perfectly (all that is not easy to do) coaxially to the bore; it is the deformation and thus unbalancing caused by inertial force during accelleration. Those "forces which ruin our groups" can be mitigated in 3 ways assuming we are using proper accuracy enhancing loading techniques (commonly referred to as "benchrest techniqes"); use a better designed cast bullet, use as slow a burning powder as needed for consistent ignition and the velocity desired and, lastly, to use a slower twist.

I use all 3 methods in my 14" twist Palma rifle. Match .308W J bullets of 168 gr usually have a velocity of 2550 - 2600 fps. I'm pushing the 160 gr 311466, a traditional GG boolits at 2600 fps with excellent accuracy. That is pretty much equal to jacketed bullet performance. With faster twist rifles of 7.8 - 10" in particular, some of us are pushing the velocities higher but the RPM threshold catches up eventually. It is evidenced by those pesky little flyers and non linear expansion of groups size at longer ranges (most noticeable between 100 and 200+ yards).

Using PP'd bullets in the faster "standard" twist barrels the same can be relatively easy to accomplish, i. e. equalling jacketed bullet velocities with good or equal accuracy. Doing so with "traditional GG boolits is obviously much more difficult to accomplish.

Larry Gibson

[303Guy]

On the heating of the boolit, I've experienced extreme barrel heating which includes the suppressor body with a certain load but with a slight increase in powder charge that heating stopped. By extreme heating I mean a 22 hornet heating a barrel as fast as a 308 does. The suppressor stayed cool too.

I've also experienced a bullet stopping in the bore then basically just slipping out with a nudge from the cleaning rod. This bullet had heat staining on it's jacket. Another one that did not stop in the bore melted itself onto the nylon fabric catch medium. That's purely surface heating from friction in the bore. The bullet that stopped had expanded its jacket so much as to jam itself. These were light loads.

The main difference between paper patched boolits and plain cast is the surface in contact with the bore can take higher temperature with paper.

[45 2.1]

But what then is the cause of inacuracy during flight (external ballistics) when we push velocities above those "accuracy loads in the older ( Lyman #45 manual)" now that you've explained the reason? Larry Gibson

When you believe the concept of barrel harmonics you will begin to understand more.


All in good time grasshopper..

Hee hee...Good one Nrut..... Thanks.


The boolit is under compression, not tension. Not outside the barrel it isn't, see, that's what got me thinking. Air resistance acting on the nose might be compression, but centripetal acceleration acts on the boolit metal, and the boolit metal has to push BACK to keep from flying apart, so it is in tension outside of the barrel.
Gear

You will note that loads with the 50/50 ww/Pb alloy is past the yield strength (in the rearward part of the boolit) of the alloy with almost any of my high velocity loads. The boolit was/is permanently deformed with no return to the plastic stage. It isn't going to spring back any. There is no tension loading here...at all. Measurement of the boolit pre firing and retrieval afterward in a suitable recovery medium show this.



Again, grain structure affects strength of both compression and tension in similar ways as far as I understand it. Gear

You do realize that grain structure is dependent on alloy constituents and cooling rate..........


Ah. Buffer. It's amazing what buffer can do to increase useable velocity range in normal cast boolits. Almost makes a gas check superflous in some instances. So why is that? Keeping the base square at muzzle exit? Absorbing shock? Preventing gas-cutting during the transition into the rifling? All of the above? Gear

You also should realize that buffer removes the boolit base interface at the muzzle.

[303Guy]

You also should realize that buffer removes the boolit base interface at the muzzle.This is evident from my recovered paper patch boolits. With buffer the patch base does not come off the boolit. With soft alloys I cannot say the boolit base is undamaged at launch into the bore.

[Larry Gibson]

45 2.1

I understand the concept of barrel harmonics quite well. However do you really think a target weight barrel (Schnieder barrel) that shoots 150, 155, 168 and 175 gr match jacketed bullets at velocities of 2650 - 2950 fps into less that 1" at 200 yards (10 shot groups BTW) and 10 shots with a cast 311466 bullet at 2357 fps into 3.1" (1.5 moa) at 200 yards (a 10 shot group BTW) will then put the same bullet into 14"+ group (10 shots BTW) simply because the velocity is increased another 100 fps because of barrel harmonics? Considering this rifle has never shot any load, including the worst of foreign made 7.62 milsurp ammo, any where close to that bad. And that I turned around and shot another 3 moa 10 shot group with the afore mentioned load after the 14"+ group you still want to think it's barrel harmonics? Well frankly, I don't and every other knowledgeable match shooter who I asked about it said something like "barrel harmonics....with that barrel and rifle...you've got to be kidding!"

Funny that only the faster twist 10 and 12" barrels had "barrel harmonic" problems with that load and the 14" twist barrel didn't have any problems. Funny how no one has posted any 10 shot groups anywhere near as good as the 14" twist barrel groups I posted using a cast bullet in a 10" twist at 2600 fps. Perhaps all fast twist barrels have such "barrel harmonic" poblems, eh?

I think you're grasping at a very thin straw with that one......as in this case with my 12" twist M70 target rifle "barrel harmonics" is a dog that doesn't hunt........

Larry Gibson

[Bret4207]

You also should realize that buffer removes the boolit base interface at the muzzle

Now THAT is something I'd never considered before! Interesting.

[45 2.1]

45 2.1 I understand the concept of barrel harmonics quite well. However do you really think a target weight barrel (Schnieder barrel) that shoots 150, 155, 168 and 175 gr match jacketed bullets at velocities of 2650 - 2950 fps into less that 1" at 200 yards (10 shot groups BTW) and 10 shots with a cast 311466 bullet at 2357 fps into 3.1" (1.5 moa) at 200 yards (a 10 shot group BTW) will then put the same bullet into 14"+ group (10 shots BTW) simply because the velocity is increased another 100 fps because of barrel harmonics? Larry Gibson

In reference to the above blue statement:
Considering your refusal to use a fitted boolit in your tests AND from what Bass reported on your actual boolit/nose size you used (which had a pretty small nose diameter, much below the common ideal).... YES. However this is not the topic of the thread and doesn't need to be here. Start your own thread and pontificate whatever you want... provided anyone will listen.

[geargnasher]

[snip]

You will note that loads with the 50/50 ww/Pb alloy is past the yield strength (in the rearward part of the boolit) of the alloy with almost any of my high velocity loads. The boolit was/is permanently deformed with no return to the plastic stage. It isn't going to spring back any. There is no tension loading here...at all. Measurement of the boolit pre firing and retrieval afterward in a suitable recovery medium show this.

No, no. I meant AFTER the boolit clears the barrel, like the fellow who shot weak-jacketed .223s at nearly 4K fps from a (presumably 8 or 9" twist) and they exploded just out of the muzzle, we think possibly because of "centrifugal" force exceeding the tensile strength of the jacke and core material, probably also exacerabated by depressurization at the muzzle and transitional forces as well, but same concept as I was exploring with plain cast at just beyond "rpm threshold" conditions. Basically I was wondering if a plain cast boolit experiences enough "centrifugal force" just beyond the "RPM threshold" to deform in flight, i.e. enlarge like a drive tire on a top fuel dragster. I just wanted to clear up the misunderstanding, after running the numbers I'm pretty certain normal cast boolits can't be fired fast enough to deform them significantly in flight, so moot point.

You do realize that grain structure is dependent on alloy constituents and cooling rate..........
Yes, of course I do, but the tensile and compressive strength, as far as I am aware (and I'm no metallurgist), are very similar with identical batch samples no matter the treatment to the batch.

You also should realize that buffer removes the boolit base interface at the muzzle.

Yes I do. The moment I realized that, I learned a LOT. I have one old rifle with a "truck floorboard' crown that shoots MUCH better with COW or BPI original in the proper density. I suspect it would improve most any military crown provided the lands inside the muzzle weren't worn to a bellmouth taper. A card wad punched from .060" gasket material or even milk jug plastic aids accuracy of plain-based .45 straightwall calibers significantly with smokeless powder, especially when combined with any other filler, even though the recovered boolit bases still show significant "dishing".

...Gear

[Larry Gibson]

45 2.1

The test I referred to was the recent one using the very well fitting 311466. I'm assuming you are referring to the 311291 I used in a test several years back since you seem fixated on that test. The same "ill fitting" 311291 that both Bass and I pushed up to 2200+ fps with sub 2 moa accuracy in 10" twist '06s. I pushed it to 2300 fps with the same accuracy in 3 different '06s with 10" twists. We both did it with that "ill fitting" 311291 using slow burning powders (in liu of the medium burning 4895 used in the origianl test you refer to); exactly as I said was one of the ways to push the RPM threshold up in fast twist barrels. Yup, that sure was an "ill fitting 311291" to use in the old 10" twist '06 and still getting sub 2 moa accuracy at 2200 - 2300 fps, yup pretty darned "illfitting" it was. Perhaps you could show us just how good your groups are at 2200- 2300 fps or perhaps 2300+ fps with a perfectly cast and fitting 311291 out of a 10" '06? Now I wonder what we could do also using a properly designed bullet? Probably the 2400+ fps we both did with the LBT bullet!

No, 45 2.1, great care was taken to ensure the 311466 "fit" all 3 rifles used in the recent test (10", 12" and 14" twist barrels). Obviously you have correctly concluded that "barrel harmonics" is not the problem since you've reached for another straw. Sorry but this dog doesn't hunt either because the bullet you refer to is not the one I refer to and used.

BTW; I do have another thread, started it myself. It has more pages and posts (not that that really means anything) than this one so apparently someone "is listening". Why don't you go over there to my thread and further discuss this topic since it was you, in post #54, that brought me, by name, into this conversation and thread with you. Be glad to have you over on my thread to discuss it.........

Larry Gibson

[45 2.1]

Basically I was wondering if a plain cast boolit experiences enough "centrifugal force" just beyond the "RPM threshold" to deform in flight, i.e. enlarge like a drive tire on a top fuel dragster.

Not that several of us have noted from recovered boolits at so called RPM units of 230,000 and above well into the jacketed performance range.

On anther note: A 311466, fitted full body boolit with infinitesmal nose.... just imagine that. A contridictory statement if there ever was one.

[Larry Gibson]

45 2.1

On anther note: A 311466, fitted full body boolit with infinitesmal nose.... just imagine that. A contridictory statement if there ever was one.

Huh? Contradicting what?

Larry Gibson

[geargnasher]

Basically I was wondering if a plain cast boolit experiences enough "centrifugal force" just beyond the "RPM threshold" to deform in flight, i.e. enlarge like a drive tire on a top fuel dragster.

Not that several of us have noted from recovered boolits at so called RPM units of 230,000 and above well into the jacketed performance range.


Thanks for the info, rudimentary calculations support that fully. I shall wonder no more.

Gear

[leftiye]

Bagtic,

Again (as before), most of your points do not detract from what I have said. You may not agree that heat caused by deformation during engraving is sufficient to cause softening of the lead, [but you state that setback causes a lot of heat] nor that friction from spinning of the boolit causes mentionable heat, nor that friction from passage down the barrel makes much heat, You only state your opinion that you disagree, and then mention other sources of heat (gas on base of boolit, nose slump -offset) that occur during firing. These other sources do not diminish the friction, engraving, rotational sources of heat, they actually promote my argument by providing additional heat, thus making softening of the lead due to heating more probable.

Air resistance does cause heat. The SR71 develops skin temperatures of 600 degrees at about the same speed as a bullet moving 3000 Fps (2160 mph) at 90,000 feet altitude. The particular example of freshly fired boolit being hot that I gave however was originally offered by a board member here, and the boolit was stopped and bounced back by a tree stump. It hadn't been airborne more than a stated 30 yards or less.

Remember, lead alloys anneal at about 300 degrees F. Melting may not be in the adjacent neighborhood, but where does softening begin? Remember also that after engraving in any lead boolit regardless of alloy - the displaced lead is at the softness of pure lead. A head start on softening in the skin of the boolit.

[Bret4207]

Remember, lead alloys anneal at about 300 degrees F. Melting may not be in the adjacent neighborhood, but where does softening begin? Remember also that after engraving in any lead boolit regardless of alloy - the displaced lead is at the softness of pure lead. A head start on softening in the skin of the boolit.

Interesting. Isn't time a factor though? IOW, lets say we have a boolit that's HT to 20 Bhn. Between compressive forces and friction we find the boolit after being shot at a high temp. The first question would be is the temp high enough to soften it and the second would be when did the temp climb? There's a time factor involved I believe, that is the boolits doesn't instantly heat as the energy is transformed. It takes time for the heat to travel, doesn't it? And as the heat travels the rest of the boolit becomes a heat sink. So was the skin of the boolit at a much higher temp or what?

On the work softening of lead alloys, are you saying any alloy work softens to the softness of pure lead? If I understand that correctly than what is the use of going to harder alloys or HT because on firing, even a very well fitted boolit changes some and that implies the whole boolit would soften. I must not be reading it correctly.

[leftiye]

Brett, It depends which end of the tube you look into. The boolits do not instantly heat up all of the way through, but a sizeable amount of that heat is created on the boolit's surface due to distortion, friction, bad breath, etc.; and then - after leaving the barrel - this heat soaks into the rest of the boolit. So the heat from most of these sources (not from bad breath) is originally concentrated at the skin of the boolit, and therefore temp is much higher initially.

Yes, once the grain structure created by heat treating or water dropping is broken down, then whatever alloy that is (lead/tin/antimony alloy that is) is then the hardness of pure lead. This softening from deformation only applies to the portion of the lead that is stressed beyond its limits of elasticity (smeared) - the surface or skin.

The rest of the boolit is still hard. The whole boolit would be softened if it reached 300 degrees, but as the heat sinks in, the portion of the boolit that ever gets that hot stops occurring because the actual temperature lessens as the heat is dissipated into more and more lead.

What I'm leading to is asking - Does this occur when pressure, velocity, loads from spinning the boolit, and etc. reach a given point? There is a concrete combination of factors that do cause failure. Is heat not one of those factors? Doesn't it appear that most of the problems associated with loss of accuracy seem to parallel "fragile boolit" issues?

[KYCaster]

Yes, once the grain structure created by heat treating or water dropping is broken down, then whatever alloy that is (lead/tin/antimony alloy that is) is then the hardness of pure lead. This softening from deformation only applies to the portion of the lead that is stressed beyond its limits of elasticity (smeared) - the surface or skin.



Wouldn't the annealed boolit revert to the same hardness as the basic alloy. With the alloying elements(Sb, Sn) added, I don't see how it could achieve the same hardness as pure Pb.

How could my 9 BHN WW ever reach 6 BHN without losing some Sb?

Jerry

[geargnasher]

[snip]
What I'm leading to is asking - Does this occur when pressure, velocity, loads from spinning the boolit, and etc. reach a given point? There is a concrete combination of factors that do cause failure. Is heat not one of those factors? Doesn't it appear that most of the problems associated with loss of accuracy seem to parallel "fragile boolit" issues?

My question as well, in a nutshell.

I really don't think that any melting or even significant softening occurs to the driving surfaces in most cases to cause this failure, but SOMETHING happens, and it happens at a certain point regardless of how well the boolit fits the throat. Even breech-seated boolits have distinct failure points when velocity reaches a certain point, and that point is well below paper- or copper-jacketed performance.

Recovered boolits don't usually show any physical signs of engrave damage, but I haven't done much of a study of boolits known to have been fired well above the "rpm threshold" to see.

Here's some more food for discussion: While water has a high specific heat, meaning it takes a lot of calories to change it's temperature, pressure affects ice very much. Take the blade of an ice skate, for instance. When you're watching a hockey game or skate performance, you don't realize that the skaters are actually traveling on liquid water, since the pressure and frictional heat from the blades melts a few molecules of the surface of the ice almost instantly, even as quickly as the skate travels across it.

Now consider that recovered patch confetti has ZERO evidence of even being scorched except for maybe the base and then only with black powder, and it takes IIRC 451 degrees to reach the flame temperature of paper, we can assume that a paper-patched boolit never gets hot enough to affect temper at all, and an unpatched one wouldn't either unless the friction at the drive edge of the land is enough to melt/abrade a very small layer of lead.

Gear

[felix]

Pressure, Gear, pressure! Your skate example says it gracefully. Hockey skate blades are wide and short, racing skates have long and thin blades. Figure skates have saw-toothed fronts on the blades, and are in between hockey and racing styles for the other dimensions. Consider these blades as rifling lands and the projectiles as ice. The pressure is pushing the rear of the projectile (in the center after movement begins) and that squishes the "ice" into the "blades". Paper is an abrasive and keeps the surfaces clean of any sticky stuff, like lead, copper, etc. ... felix

[felix]

Yep, catching that 220 Krag bullet was by me (5010 powder in 308 case). So dang hot it was unbelievable. I still have that sucker somewhere. Lucky I saw it in the first place. Catching it was no problem because the speed was no more than say 60 mph. It happened during my baseball days, so I was agile enough to react in time. ... felix

[303Guy]

Heat! Mmmm.... ? Compress anything or accelerate/decelerate anything and it gets hot! A lead boolit is getting both those plus the friction caused by the bore containing the lateral expansion! There must be a little heat transfered to the boolit from the hot gases behind it.

I posted a phot earlier of a boolit that had a distinct shear plane in it where the boolit portion ahead of the shear had offset relative to the portion behind the shear. And that was a paper patched boolit.

[leftiye]

Yep, catching that 220 Krag bullet was by me (5010 powder in 308 case). So dang hot it was unbelievable. I still have that sucker somewhere. Lucky I saw it in the first place. Catching it was no problem because the speed was no more than say 60 mph. It happened during my baseball days, so I was agile enough to react in time. ... felix


Thought that was you Felix. Err..."sticky stuff" Hmmmm. Maybe a heat/pressure combined sliding scale (sounds hard to avoid?)? Bullshop's 3600 fps 225107 obviously avoided this somehow I'm thinkin'. Think short boolit, goood lube.

Gear, one more vote towards paper insulating the paper patched boolit? Granted, DrB's spreading the pressure concept probly gets in there too! Them driving edges are only about .004" wide (or less, maybe as little as .002").

[leftiye]

I may be wrrrrrr - (you know) about work softened lead being the hardness of pure lead. I simply put down what I understood. Thinking about it, it could be correct, or maybe not. Lead containing antimony in an alloy (not heat treated) probly still forms some crystalline structures upon air cooling, thus hardening the boolit somewhat. Does anyone know? I'm suspecting that other alloys like copper, and tin may harden by another mechanism as they don't heat treat. Anybody?

[leftiye]

Would something like packing peanuts slow a boolit gently enough to avoid damage whilst shedding velocity? Maybe could be a way to test what boolits that have "lost it" look like compared to accurate loads with same boolits. It could be fun finding the boolits though.

[303Guy]

No, not really. Most of the heat obtained by the projectile is from the powder burn. ... felixMost of the heat? As in heat transfer through the base or indirectly? What is the actual flame temperature within the chamber? I know that a lot of heat is transfered into the case but that has a larger surface area and a relatively small mass. Ejected cases from a self loader can be uncomfortably hot.

[Bret4207]

Leftiye, I don't see how any boolit at, say, 14 Bhn AC can possibly soften to 8 Bhn. That's just no logical. And while I can see the argument for work softening, I think it's probably a lot more complex than as presented. This is likely another of those areas where we see the results, but never really understand the causes.

[BABore]

If a heat treated boolit would somehow anneal and soften due to air friction or combustion gases, would you not see the difference in expansion media, game, etc. Not something I've ever seen.

BTW, if you fully anneal HTWW's, they will test out at almost pure lead hardness for the fist 2-12 hours. They then creep back up to their normal 11-14 bhn state. One of the reasons it's best to not cast, load, and shoot immediately. Even air cooled boolits benefit from a week or three rest before using. Lower the antimony level and the wait time increases.

[44man]

Granted, I am not playing in the high velocity ranges, just revolvers and single shot pistols since I long ago sold the rifles I shot cast from.
But there must be some connection.
If I shoot too soft I get very large groups. If I oven harden, groups tighten very nice with 3 out of 5 in one ragged hole but I always get those fliers.
If I move to air cooled WW metal, groups are open again with fliers. If I water drop, groups will be very small. If I add a small amount of antimony and tin, groups get even better.
If I go very soft like lead and tin, my bores get a lot of leading and only BP will work. Maybe 5744 would ease up on the boolit.
Either way, the boolit must be holding hardness in the rifling.
I have been to over 1800 fps but admit I don't know what happens when the envelop is pushed.
The flame front with smokeless in high intensity cartridges will exceed the melting point of steel and is why throats and leades get eroded. Yet a paper wad, filler or a paper patch will not burn. The ability of the steel to suck away the heat and the larger diameter the barrel, the more heat it can draw off until the gun is shot so fast the barrel glows at which point the barrel is ruined fast. I don't think anyone would shoot cast when rounds cook off! [smilie=l: That is why a Gatling works better. Many barrels and water cooled.
For normal shooting with cast, the barrel will not get very hot and I don't think a lead boolit with the lower friction will ever get as hot as a jacketed bullet.
It seems comparisons of cast to jacketed creeps into the discussion.
My question will always be; do you reach boolit failure with too much spin or have you just exceeded the stability point of a given boolit?
Working loads with any bullet or boolit in any gun will show groups start to open once the sweet spot is passed and I know darn well I am not reaching bullet destruction although a point can be reached with some guns so you get a smoke trail instead of a bullet because the bullet was not designed for the velocity. Thin jackets and dead soft cores but just maybe the stability point has been far exceeded to start with.
I suppose what I am trying to say is a boolit pushed past stability can go crazy yet not exhibit real damage.
This has been interesting but I can't see pushing a boolit to 3000 fps when it is just right at 1500 fps with the twist you have.
I am old school and match a boolit to the twist or the twist to the boolit. I match hardness of the alloy to the powder and initial pressure rise.
If you want 15,000 mph to escape into space, slow the twist! [smilie=l:

[felix]

Time is the major factor in heat treating, for hardness or for softness (annealing). There is not enough time for the boolit to do anything in that arena when shot, except when the lead actually melts. A genuine flier is the guaranteed result of a surface destruction should there be no corruption in the barrel before the shot. Playing with paper patched boolits should eliminate the dirty barrel problem, and allow better testing of what we are talking about in this thread. ... felix

[Larry Gibson]

44man

"If I shoot too soft I get very large groups. If I oven harden, groups tighten very nice with 3 out of 5 in one ragged hole but I always get those fliers.
If I move to air cooled WW metal, groups are open again with fliers. If I water drop, groups will be very small. If I add a small amount of antimony and tin, groups get even better.
If I go very soft like lead and tin, my bores get a lot of leading and only BP will work. Maybe 5744 would ease up on the boolit.
Either way, the boolit must be holding hardness in the rifling.
I have been to over 1800 fps but admit I don't know what happens when the envelop is pushed. "

Consider, given the same load and velocities (read that acclereation rate), that the softer alloys deform more from unwanted obturation, setback, sloughing etc. and thus will be more unbalanced on muzzle exit. Then during the external ballistic phase the RPM (centrifugal force) will have more adverse affect of the more unbalanced softer alloyed bullet in flight. Accuracy will suffer with the more unbalanced bullet. It's pretty much that simple.

Larry Gibson

[44man]

Time is the major factor in heat treating, for hardness or for softness (annealing). There is not enough time for the boolit to do anything in that arena when shot, except when the lead actually melts. A genuine flier is the guaranteed result of a surface destruction should there be no corruption in the barrel before the shot. Playing with paper patched boolits should eliminate the dirty barrel problem, and allow better testing of what we are talking about in this thread. ... felix
Time is very important. I agree.
What baffles me is when I recover a softer batch of boolits that do not group well and compare them to those that shoot well, I can't see any difference. No slump and clean rifling marks without skid.
Just a few points of BHN? What is going on? Could it be a difference in bore friction?
I can take an oven hardened 50-50 GC boolit and shoot it better then an air cooled WW, GC boolit even if BHN is so close it just can't count.
I see this junk with almost no changes in alloy or hardness so just how does anyone sort this out when really pushing cast?
Could .005% of some metal in the boolit will let one guy do wonders while another fails?
I am so glad I don't have to come up with answers! :bigsmyl2: I am old and lazy and quit when a gun shoots best.

[Bret4207]

And it baffles me that I've tried the ultra hard HT alloys from 20-35 Bhn and they shot worse for me. For you they work great, for me they sucked and I want nothing to do with them. I imagine our fitting methods differ.

[44man]

And it baffles me that I've tried the ultra hard HT alloys from 20-35 Bhn and they shot worse for me. For you they work great, for me they sucked and I want nothing to do with them. I imagine our fitting methods differ.
That is exactly why we all have different results and no matter how much theory and math is used, we can't match what each other does.
I really, really believe that none of us can do the same things. We should accept that anything posted is only a trial to test.
Instead of arguing, it is better to agree with each other, shake hands, be friends and understand nothing works the same.
You do things I can't and I do things you can't and it should be fine for us.
We post and the poor guy starting still has his job cut out for him, time to think and work, no plate of ice cream set in front of him! :bigsmyl2:

[Larry Gibson]

And it baffles me that I've tried the ultra hard HT alloys from 20-35 Bhn and they shot worse for me. For you they work great, for me they sucked and I want nothing to do with them. I imagine our fitting methods differ.

Check my last post on the RPM threshold thread, it may help your understanding.

Larry Gibson

[geargnasher]

I may be wrrrrrr - (you know) about work softened lead being the hardness of pure lead. I simply put down what I understood. Thinking about it, it could be correct, or maybe not. Lead containing antimony in an alloy (not heat treated) probly still forms some crystalline structures upon air cooling, thus hardening the boolit somewhat. Does anyone know? I'm suspecting that other alloys like copper, and tin may harden by another mechanism as they don't heat treat. Anybody?

The "another mechanism" is really the same mechanism. Certain impurities in lead, such as arsenic, copper, and IIRC calcium, selenium, tin, and sulfur "refine" the grain structure of the lead, making smaller shear planes. I posed the question of sulfur on Larry's RPM thread, hopefully someone with more understanding/experience than I have with it will expound.

Gear

[white eagle]

That is exactly why we all have different results and no matter how much theory and math is used, we can't match what each other does.
I really, really believe that none of us can do the same things. We should accept that anything posted is only a trial to test.
Instead of arguing, it is better to agree with each other, shake hands, be friends and understand nothing works the same.
You do things I can't and I do things you can't and it should be fine for us.
We post and the poor guy starting still has his job cut out for him, time to think and work, no plate of ice cream set in front of him! :bigsmyl2:

:drinks:

[303Guy]

I'm suspecting that other alloys like copper, and tin may harden by another mechanism as they don't heat treat. Anybody?When I added copper to whatever my alloy was it did strange things. I could measure the change in hardness in something like half hour intervals. Heat trwating only speeded up the initial hardening by about an hour or two then the differences would be gone. It was pretty tough and malleable and had good hold together on impact. Trouble is, I have no idea what was actually in that batch.

P.S. Surely this thread is worthy of being a sticky?

[DrB]

Guys, this certainly has ranged far afield from what I intended, but its been lively and some good thoughts shared. Looks like folks are having fun, so good. :)

I wasn't confident in some of the thoughts re "explosive effect" and so crunched a few more numbers and played with some 35 gr vmaxs on the range with milk jugs, recovering the fragments (in each of three jugs filled with water there were no perforations other than the entry hole at 3200fps). For the most part, I think the effect of spin comes down principally to preloading a thin unbonded jacket, such that on impact the jacket shreds and fully exposes a soft lead core. At higher velocities during impact with a dense target the dynamic pressure is so far in excess of the core ultimate strength (and centripetal loads) that the core basically flows and is turned to dust/small particles which rapidly dump their energy. I expect a paper patched hollow point of soft alloy would show the exact same explosive effect as a jacketed varmint round at comparable velocity without any jacket... Don't know if pp would let you get the velocities, but a nylon sabot should, I would think.

Bret, I'm dubious if this can happen to anything like the same extent with fmj, without far higher velocities and rpms, as the ogive area is far less loaded and the jacket relatively stronger. If nothing else I'd expect the nose to survive... And, unlike my vmaxs, id expect big chunks of the projectile to exit the offside.

Re, accuracy due to internal/departure ballistics, neglecting gun movement, seems to me you've got 1) barrel vibrations/harmonics which cause variations in the POI due to barrel pointing at bullet departure, 2) asymmetric venting effects causing lateral shove due to bullet and/or crown imperfections/damage (I took a swag at these on the bullet base sticky) and 3) lateral "fling" due to conservation of momentum. I calculated the group opening due to this last on the prior rpm thread. I gave an example relevant to my own recent range test that showed the impact to accuracy from bullet imbalance from this effect alone could be significant (.6 moa from a small fraction of a grain of imbalance). I think it would be interesting to compare this to mann's results page ~ 185 as I think they should compare okay, absent base venting (mann cut the side of the base of the bullet), plus a little "hooking" of the trajectory due to gyroscopic effects... The latter two will be at right angles to the fling so should be discernible.

I agree with 303guys observation about buffer reducing the impact of gas venting at bullet crown departure, which is an interesting thought... And I think it probably can play a significant role with gas cutting as well.

Re external ballistics, if you have completely excluded effects such as wind and velocity sd + gravity on group size expansion then there are two different phenomenon I can think of that could theoretically cause a non constant increasing angular group size with range for a spin stabilized body... But a significantly damaged/ imbalanced bullet will open up groups at 25 yards (etc) long before it gets out there, and these two phenomenon don't require a grossly imbalanced body.

If you get <1 moa at 100 yards your bullet actually left the muzzle pretty well balanced... If it wasnt it would have flung on separation from the crown and moa would have opened up. You can bound how well balanced it would have to be at worst using my post on the prior thread.

I am sceptical about heat being a factor... Heating would have to be due to plasticity throughout the body as the rate of diffusion of the heat is too slow relative to flight speed for the heat to be coming from the surface of the bullet. Stick the nose of a long bullet in a blowtorch while holding the base and count till you have to drop it (lets do use someone elses fingers for this experiment :))... I'll bet you can get past a second, which is long enough for a bullet at 2000 fps average velocity to fly over 600 yards.

If you had that much heating from plasticity (other than on target impact) I suspect you would already be having major problems from the associated bullet damage. It would be interesting though to shoot a bullet into a trap and throw it on a cabine tree style tester right away. If the deformation and heat didn't impact hardness I'd be dubious anything in the barrel could other than superficially. Of course, if the hardness was affected it wouldn't necessarily mean anything at all re what the bullet did in the bore or in flight.

Anyway, those are my thoughts. I've got the equations for centripetal stress and dynamic pressure (which bounds/approximates the stress due to impact in a fluid medium) if anyone has an interest. For the core, it's a similar story as rotational vs translational energies as the stresses due to impact far exceed those of spin relative to ultimate stress.

Best regards,
DrB

[303Guy]

Heating would have to be due to plasticity throughout the body ...Is there enough compression within the barrel to heat the boolit while in the barrel? Meaning that such heat would disappear once the pressure is relieved at muzzle exit? I would think there is nowhere near enough pressure to significantly raise the core temperature.

[BAGTIC]

Bagtic,


Air resistance does cause heat. The SR71 develops skin temperatures of 600 degrees at about the same speed as a bullet moving 3000 Fps (2160 mph) at 90,000 feet altitude. COLOR="lime"]But it doesn't achieve that temperatures in a few thousandths of a second. It requires sustained flight of long duration. [/COLOR]ButThe particular example of freshly fired boolit being hot that I gave however was originally offered by a board member here, and the boolit was stopped and bounced back by a tree stump. It hadn't been airborne more than a stated 30 yards or less. Which would suggest it hadn't been heated by air friction I have had bullets bounce back and hit me. Once from an oak tree and once from a tire carcass. They too were rather warm but I would say no warmer than they would have gotten in a mayonaisse jar on the front porch of Funk & Wagnalls. The fact that they might feel warm is subjective. It gives no indication of HOW warm they really were and is more indicative of the sensory perception of a human finger than an indication of heat rise. I have also had more than one freshly ejected case skitter down the inside of my shirt. Some of them left a temporary red mark but I have yet to experience one so hot it would sputter if spit on.

Perhaps some of the paper patch shooters can tell us how they keep their paper jacketed bullets from turning to char while going down the barrel. That paper must create a lot of friction.

Remember, lead alloys anneal at about 300 degrees F. Melting may not be in the adjacent neighborhood, but where does softening begin? Remember also that after engraving in any lead boolit regardless of alloy - the displaced lead is at the softness of pure lead. A head start on softening in the skin of the boolit.

Consider also that many 'hard' bullet alloys actually melt at lower temperatures than pure lead. So should not the effects of friction and gas cause them to soften faster tha pure lead bullets?

[leftiye]

Thanks. Nice color BTW.

[wiljen]

After further review, I stand corrected. There is new discussion here, just the stuff on the RPM theory seems to be a rehash. Larry will be compiling an article on such for Castpics so hopefully we can remove that from the context here for the time being. I am going to re-open this thread with the understanding that if it becomes "The RPM thread" round 2, it will go away for good.

[BAGTIC]

No, not really. Most of the heat obtained by the projectile is from the powder burn. ... felix

Then the solution is at hand. Insulate the base of the bullet. Stick a small piece of paper or aluminum foil on the base of the bullet to protect it from the powder gases.

Come to think of it do saboted bullets get hot?

[BAGTIC]

And it baffles me that I've tried the ultra hard HT alloys from 20-35 Bhn and they shot worse for me. For you they work great, for me they sucked and I want nothing to do with them. I imagine our fitting methods differ.

It may be that when shooting the ultra hard HT projectiles you should try a larger than normal diameter. If you have been shooting softer bullets you may have been taking advantage of their tendency to expand upon firing to fit themselves to the bore? With the harder (stronger) bullets that is less likely to happen so it is more important that the bullets be sufficiently large diameter to begin.

The same is true of jacketed bullets in that with otherwise identical bullets the ones with hard cores develope less pressure than the ones with soft cores.

[blackthorn]

Quote:"It may be that when shooting the ultra hard HT projectiles you should try a larger than normal diameter. If you have been shooting softer bullets you may have been taking advantage of their tendency to expand upon firing to fit themselves to the bore? With the harder (stronger) bullets that is less likely to happen so it is more important that the bullets be sufficiently large diameter to begin.

The same is true of jacketed bullets in that with otherwise identical bullets the ones with hard cores develope less pressure than the ones with soft cores. "

And thus the oft repeated advice to ensure "fit" from the outset!

[303Guy]

And thus the oft repeated advice to ensure "fit" from the outset! Looking at some of my past pictures I realize something - harder alloy boolits suffer less base cupping and trailing edge feathering.

http://i388.photobucket.com/albums/oo327/303Guy/Two-GroovePP28grAR220910grBran2.jpg Soft.

http://i388.photobucket.com/albums/oo327/303Guy/Two-GroovePP30grAR220957grBran.jpg Hard.

Both from same gun.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-376F.jpg Hard.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-875F.jpg Soft.

[DrB]

303guy, were you ever able to determine whether the paper patch facilitated the extrusion at the base edge? It is interesting that you can see the imprint of the paper patch on the base of that last bullet.

[303Guy]

Very good point, DrB. The paper impression into the base would quite possibly increase the extrusion effect. The fact that paper is soft would likely allow the metal to flow or be dragged more readily. To put it to the test would require firing and capturing two identical size and weight boolits, one patched and one not, to see what happens. A large number of comparisons would start to mean something. Mmmm.... that sounds like WORK! But it could be done. I only have to machine a few oversize castings to match the patched boolit with the same alloy. Would you mind reminding me in a few days? (Busy with income tax returns and work right now!)

[Multigunner]

The British tested every aspect of bullet heating while developing the .303 cartridge, they had to because both smokeless propellants and jacketed bullets were a new thing and early results were lousy.

They found that if a powder did not leave a smidgeon of carbon fouling, and the test batches of cordite burned extremely clean, then direct bullet jacket to bore steel contact overheated the jacket by friction alone, breaking the bond with the lead core and sometimes liquifying the outer surface of the lead core.
They could see a halo of vaporized lead thrown from the base by centrifical force.
A tiny hole drilled near the base allowed a plume of lead vapor to escape.

They tested to be sure it was mainly friction that overheated jackets by ramming bullets through the bore using a hydraulic ram then measuring heat of bullet and barrel.

Several methods were tried to avoid partially liquifying the lead core. One was to insert a insulating layer between jacket and core, workable but costly.

They finally added mineral jelly to the cordite formula, the mineral jelly (only rifle and artillery cordite used mineral jelly, pitol cordite and blank cartridge cordite do not) left a microscopic carbon layer to prevent direct contact. Still the first shot from a clean dry barrel usually went wild.
They then increased jacket thickness and added alloying metals to the lead core material.
Together these steps did the trick.

How much the heating of modern bullet designs comes from friction is hard to say, but I would expect that its most.

When the .220 Swift was first pushed past 4,000 FPS bullets sometimes flew apart within feet of the muzzle, a white trail of vaporized lead was shown by high speed photography.
The bullet flew apart due to centrifical force, but could not have done so if not heated to the melting point of lead by friction.

The hotter the propellent the more heat the bullet is already exposed to by the time its velocity reaches the point where friction heats it to its maximum temperature before leaving the bore.
Air resistence may add heat to the nose but passage of air would also carry heat away from the body.

Another minor factor might be heat of compression due to bump up and engraving forces at the begining of its trip.

If there significant blowby this can also overheat the already hot jacket, this was the major cause of shed jackets stuck in the bore. The higher the propellent temperature the more likely that blowby would damage the jacket.
The over the charge card wad of the .303 reduced blowby, without the card the thoat would be destroyed in 1/6th the number of rounds fired.

[DrB]

Multigunner, sounds like you've got one or more great historical references... Can you please share some titles/authors? That kind of experimental work is always fascinating to read about.

Thanks for the post!

Best regards,
DrB

[303Guy]

I concur with Multigunner. I discovered exactly what is being said in a different way. Light loads with a tight fitting bullet that would sometimes jam the bullet in the bore but would then slide out with the gentlest push. These showed heat staining on the contact surfaces. Being hollow nose, they did nit shed the jacket. Clearly, the jacket was being heated by friction and expanding to jam in the bore. One sample that did not stop in the bore melted into the catch medium. (Nylon cloth).

[BAGTIC]

The British tested every aspect of bullet heating while developing the .303 cartridge, they had to because both smokeless propellants and jacketed bullets were a new thing and early results were lousy.

They found that if a powder did not leave a smidgeon of carbon fouling, and the test batches of cordite burned extremely clean, then direct bullet jacket to bore steel contact overheated the jacket by friction alone, breaking the bond with the lead core and sometimes liquifying the outer surface of the lead core. Why didn't they have the same problem with black powder? When the first round is fired from a clean bore there is no 'carbon fouling' to lubricate the bore regardless of the powder being used. Powder fouling follows the projectile, it does not lead it.
They could see a halo of vaporized lead Lead vaporizes at 3189F degrees thrown from the base by centrifical force.At what point did they notice this 'halo' of vaporized lead? In the bore? If the hole had not been drilled in the bullet how would the lead vapor have escaped? Why does not modern ammunition experience this same melted core syndrome? If it exists we should be able to demonstrate it by firing at target close to the muzzle, before the 'melted cores' have a chance to solidify, and seing evidence of liquid splatter. Why don't we? The Hornady 7mm 120 gr SP chronographs at 3,281 fps from my 7x57 AI. It has never experienced 'melted core syndrome' It has not, yet, experienced bullets 'vaporizing' in flight. Why is that? It certainly operates at higher velocity, higher pressure, and higher temperatures than the .303.
A tiny hole drilled near the base allowed a plume of lead vapor to escape.

They tested to be sure it was mainly friction that overheated jackets by ramming bullets through the bore using a hydraulic ram then measuring heat of bullet and barrel. In 1891 where did they find a hydraulic ram able to force a bullet through a bore at 2,400 fps and 45,000 psi?

Several methods were tried to avoid partially liquifying the lead core. One was to insert a insulating layer between jacket and core, workable but costly.

They finally added mineral jelly to the cordite formula, the mineral jelly (only rifle and artillery cordite used mineral jelly, pitol cordite and blank cartridge cordite do not) left a microscopic carbon layer to prevent direct contact. The mineral jelly was added to reduce the combustion temperature of the early cordite temperatures which experienced severe throat/bore erosion. This applied to artillery firing steel projectiles which certainly were not being softened by the temperatures.Still the first shot from a clean dry barrel usually went wild. Of course. Accuracy is about repeatability and consistency. It requires consistent bullet weight, charge weight, etc. When one introduces two different bore conditions (clean/dirty) one introduces variability. If bore were cleaned between every shot such as many old time lead bullet target shooters did, that variability would have been removed. It would however have been inconvenient in combat. I am sure that if one excludes the first shot from the clean barrel the remainder would have exhibited much more uniform performance.
They then increased jacket thickness and added alloying metals to the lead core material.
Together these steps did the trick.

How much the heating of modern bullet designs comes from friction is hard to say, but I would expect that its most.

When the .220 Swift was first pushed past 4,000 FPS bullets sometimes flew apart within feet of the muzzle, a white trail of vaporized lead [3180 f degrees] was shown by high speed photography.
The bullet flew apart due to centrifical force, but could not have done so if not heated to the melting point of lead by friction. If it was due to frictional heating can we assume that it happened to every shot fired for surely that all experience the same friction? I personally have had two bullets diintegrate in the air at close[< 50 yrds] range. This out of many thousandsfired using the same gun and load over the past 50+ years. Friction sure is fickle isn't it?

The hotter the propellent the more heat the bullet is already exposed to by the time its velocity reaches the point where friction heats it to its maximum temperature before leaving the bore. Only at the very base
Air resistence may add heat to the nose but passage of air would also carry heat away from the body. So will radiation.
Another minor factor might be heat of compression due to bump up and engraving forces at the begining of its trip.

If there significant blowby this can also overheat the already hot jacket, this was the major cause of shed jackets stuck in the bore. The higher the propellent temperature the more likely that blowby would damage the jacket.
The over the charge card wad of the .303 reduced blowby,Ley's see. The brass jacket could not prevent blowby but the little paper wad could. Does that seem reasonable? without the card the thoat would be destroyed in 1/6th the number of rounds fired. From WIKI, "The Lee-Metford started to be phased out in 1895 in favor of the Lee-Enfield, which was a virtually identical design but adapted for the use of smokeless powder. The Metford pattern of rifling was shallow and subject to rapid wear when ammunition loaded with cordite was used, with barrels becoming unusable after less than 5,000 rounds. Changes included a new, deeper rifling pattern (designated Enfield pattern) and sights adjusted for the flatter trajectory enabled by the smokeless propellant." No mention of the 'marvelous new anti-melt bullet design.
Where were the British getting all of these marvelous technological devices in 1891?

[leftiye]

I wish you'd quit doing that, I can't read it.

[leftiye]

So, this heat idea may actually be having an effect? The reference to a modicum of carbon used to reduce friction would say that actual lubricants would cause much more heat reduction. But it appears that plenty of heat is available. Wow, melt lead cores inside jackets!

[BAGTIC]

If you are color blind I could try a different color.

Website boards have a lot in common with the rest of life in that much of the information on them is worth only what one pays for it. Much is opinion, speculation, conjecture none of which constitutes evidence. GIGO

I offer some evidence.

http://www.advancedimagingpro.com/print/Advanced-Imaging-Magazine/Infrared-Camera-Measures-Bullet-Heating/1$180


The boiling point of lead is 1750 C. The melting point is 328 C. All are above the measured temperatures. Aerodynamic heating of the tip was only 170 C. Note that the hot spots were in the grooves cut by the riflings lands. The spaces between those grooves where the bullet rode over the grooves was much cooler and did not glow as much as the aerodynamically heated tip.

[Nrut]

Blue would work for me...

[DrB]

Nice find, bagtic. There are several factors which affect frictional heating, though. I would really like to read multigunners sources for myself to get a better idea as to conditions and observations.

I have heard anecdotes of very high velocity >4000 fps 22 cal rounds leaving silver "rays" of lead around a target hole that were assumed to correspond to cracks in the jacket from rifling scoring. Previously I had assumed the core was spun past ultimate stress and was leaking out from centripetal force, but after calculating the stress I don't believe this is possible for the scenario.

I haven't observed the leaking lead, but if it is happening then it must be something besides just centripetal acceleration. It can't be aerodynamic, and I don't believe it can be heat transfer from the combustion gases. That leaves rifling friction? Anything else?

Best regards,
DrB

[leftiye]

So, if we go back to cast boolits, heating until softened may be possible? You only need for it to occur in the grooves made by the rifling, and then only on the edge that bears for trouble to ensue. Heating would also grossly exacerbate slumping.

Too old to be color blind and to not have it shown up at the optometrist's office. Jest a nasty color.

Had to add - Mighty nice of you to offer evidence that supports the side of the issue that you are disparaging.

[Multigunner]

From WIKI, "The Lee-Metford started to be phased out in 1895 in favor of the Lee-Enfield, which was a virtually identical design but adapted for the use of smokeless powder. The Metford pattern of rifling was shallow and subject to rapid wear when ammunition loaded with cordite was used, with barrels becoming unusable after less than 5,000 rounds. Changes included a new, deeper rifling pattern (designated Enfield pattern) and sights adjusted for the flatter trajectory enabled by the smokeless propellant." No mention of the 'marvelous new anti-melt bullet design.
Where were the British getting all of these marvelous technological devices in 1891?


Try T F Freemantle (Lord Cottesloe) "The Book of the Rifle"
From page 90



One difficulty connected with the bullet gave some little trouble at first. The heat set up by the friction of the bullet on the bore is very considerable. It was found with the experimental ammunition first made for the .303 that the first shot fired from a clean barrel was never seen or heard of again, while, when once the barrel had been fouled, the rifle shot satisfactorily. The only reason was that the friction of the bullet in being passed up the barrel developed heat enough to melt that part' of the leaden core which lay next to it. Apparently the deposit from a shot previously fired was sufficient to reduce this heating effect. The difficulty was so great that it had to be got over by thickening the metal envelope of the bullet. It could equally have been overcome, as Sir Henry Halford pointed out in a lecture delivered at Aldershot at the time, by inserting a minute layer of some non-conducting material between the leaden core and the metal thimble. Some years ago the writer was trying a series of experiments with various loads of different smokeless powders, and a bullet of normal make which gave no trouble. In testing one particular powder at the ballistic pendulum the shooting was found to be extremely wild. On firing a series of shots through a cardboard target at a distance of only 4 or 5 yards, the reason became evident. Most of the shot holes were seen to be surrounded by one or more little black cloudy marks, sometimes showing a spiral inclination, which proved clearly enough that a spattering of very fine particles of melted lead was escaping from the base of the bullet as it flew. Why the conditions of friction with the deposit of this powder were so different from those of all other powders used with the same bullet, it would be very hard to say. Mr. Metford, in investigating the vagaries of the first shot, had been able to see the bullet in the air surrounded, as it flew, by a little cloud of melted lead consisting of particles so fine that on recovering the bullet, and weighing it, it was found to have lost only one or two grains in weight during a flight of several yards through the air.
Another adverse effect of Cordite without mineral jelly was the tendency of jacket material to bond to bore surfaces so thickly that accuracy went south within 400 rounds. The thick metal fouling was so difficult to remove that barrels were often ruined in the cleaning process.
Carbon fouling then proved to be beneficial. Of course you can have too much of a good thing.

Freemantle gives only a small part of the story. There are other contemporay sources that give a better picture of the order of events.

Wikipedia doesn't really have much useful information on the development of the .303 cartridge, or its propellents and bullets.

PS
You'd be suprised just how high the engineering arts advanced during the last years of the 19th century.

[303Guy]

I wish you'd quit doing that, I can't read it. It's not alway apparent. I've just just installed a new operating system (old one got hijacked and destroyed - and the swines phoned me and offered to go into my 'puter to fix the problems they'd caused in the first place! What? They think I got money in my bank account they can steal! And they would have too!) and the screen colors make it very hard to read the green.


PS
You'd be surprised just how high the engineering arts advanced during the last years of the 19th century. It is very surprising indeed!

[Multigunner]

It is very surprising indeed!

The first use of "Spark Photography" (invented in 1850) to photograph the passage of a bullet through the air was done in 1886.

PS
Two things about paper.
Paper or cardboard wadding doesn't burn up so easily because propellents generally only create as much oxygen as they use up in combustion. No matter how hot it gets, where theres no oxygen theres no oxydation. The same principle that allows the lightbulb filament to last so long at incandescent temperatures in its vacuum sealed environment.

Paper is also a very effective insulator, copper and other bullet jacket materials conduct heat with great efficiency.

[303Guy]

The first use of "Spark Photography" (invented in 1850) to photograph the passage of a bullet through the air was done in 1886.Wow! :shock:

I'd suggest that there simply isn't enough time for heat to be transfered into paper and not much to transfer into copper. Friction will heat a copper jacket pretty quickly though (on the contact surface). Yet a hot flame under high pressure will erode lead violently in the same time. Or does it at very high velocity? Surface friction heating and melting might become more dominant at higher velocity.

[HORNET]

Charles Newton had problems with bullets coming apart in flight with the .30 Newton and attributed it to melting (or at least softening of the outer portions) of the core due to friction. He had the makers insert a paper wrapping on the cores and the problem went away. I don't know if that was due to the insulation effect or because it gave a "yield zone" for the jacket to deflect into and reduce stress riser formation which would effectively give a stronger jacket on barrel exit. A comparison of standard rifling versus the 5-R type might also be interesting, maybe in a .22-250 where I have had varmint bullets go "blue cloud" in flight.
Strange things happen to material properties under extremely short term high intensity transients of heat and pressure. There is little published data on this that I've been able to find and I suspect that variations in exact alloy composition may have a significant effect on the properties (strain rate sensitivity, heat transfer rate, etc).

[BAGTIC]

Had to add - Mighty nice of you to offer evidence that supports the side of the issue that you are disparaging.

Why not? In the search for truth there is no room for egos. The truth must out.

When using long ago references it is important to remember that those conclusions are just that, conclusions, and they they were as subject to error as we are today. The difference is that we have had more time to check, recheck and compare. Also we have much better technology.

Many great scientific discoveries and theories have been based on original error. Example, Gallileo's cannonbal experiment whereby he deduced that rate of fall is the same for cannonballs of all sizes. In a vacuum, yes, but in northern Italy , no. It was the result of the fact that with the technology available to him at the time he was unable to accurately measure the difference caused by aerodynamic drag. Remember the great Isaac Newton predicted the world will end next year and several Nobel Prizes have been found invalid because later research proved the to be erroneous..

[leftiye]

Surface friction heating and melting might become more dominant at higher velocity.

Trying not to be a yerk (yeah, it's hard), - but that's the whole point. Faster = hotter. Threshold anybody?

[Multigunner]

When theres little or no effective cooling process heat will continue to build up from any sources that create and transfer it.
When a bore has eroded sections, gas blowby adds to the heat of friction. A bullet otherwise resistent to effects of friction heating can be pushed past the tipping point by blowby.
When the Springfield 1903 .30 caliber loaded with high nitroglycerine content double base powder was in use, eroded sections allowed blowby that overheated the bullet jacket causing blow throgh of the lead core and leaving jackets stuck in the bore.
A report to the Chief of Ordnance outlined the cause and cure. Bullet manufacturing processes and thicker jackets solved the problem. Use of a much lower temperature single base pyro-cellulose powder for the 1906 .30 cartridge greatly reduced erosion.
Where stuck jacket removal tools had been part of evey Springfield cleaning kit, now only a few were issued per company for use by officers and non coms trained to use these properly to avoid bore damage.

Black Powder cartridges used bullets with lube grooves and/or surface applications of thick lubricants to reduce friction, otherwise few bullets could leave the bore intact.
Bullet seize up and blow through could still be a problem with too soft bullets and roughened bores.
Surface seasoning of the bore lessened friction by trapping microscopic globules of lubes that acted like miniature ball bearings under these pressures. The microscopic pits , visible only as a darkened surface held just enough lube to prevent or lessen metal to metal contact.
Brightly polished bores caused more friction not less as we would expect. Same principle as the crosshatch honing of automobile engine cylinders to hold lube during the firing stroke.
When in balance the rings don't actually touch the cylinder walls. A ultra thin barrier of oil seals in the high pressure combustion gases rather than metal to metal contact.

A proper BP/lead boolit bore should be even but not slick other than the slick coating of lubes.
Slick polished or burnished steel won't hold enough lube.

Paper patching of bullets served several purposes at once. Under pressure paper becomes stronger, and quickly reaches the point of relative incompressibility. Lead remains ductile far longer than paper.
Greased leather and later cloth patches served the same purpose for the round ball muzzle loaders.
Paper patching allowed duplex bullets with softer lead body and hardened lead nose sections to be used with a false muzzle for the most powerful of the muzzle loading thousand yard match rifles.
The soft body upset to push the paper jacket deep into the grooves, the paper insulated the soft lead from friction heating, the hard nose section withstood acceleration and air resistence which would otherwise deform a soft bullet nose at these power levels.
Still BP cartridges had velocity limitations.
The few hundred extra FPS of early smokeless powder cartridges pushed the older style bullets past the tipping point of consistent performance.

As for powder grain peening of bullet bases, this is a recognised factor in forensics. I've seen the effect on open base FMJ pistol bullets I salvaged from a clay bank after a hard rain. The 9mm seems to demonstrate this more clearly than lower pressure rounds, or higher pressure rounds which have tougher core alloys.
Lead is deposited in the bore in microscopic amounts every time an open base bullet is fired. The following shots carry away most of the lead from the previous shot.
The microscopic lead contamination of the bullet jacket is then scrapped away when the bullet penetrates a hard object, like wall board or doors.
A chemical that detects lead can be used to identify bullet holes that otherwise might be overlooked, or tell the difference between old nail holes and bulletholes.

PS
Another historical tidbit.
The Thermocouple was invented in 1821.

PPS


The temperature required to volatilize/boil lead is 1,740 C or 3,164 F
Vaporize is not the same as "volatilize".
Water can be vaporized by merely squirting it from a spray bottle at room temperature, it doesn't have to reach the boiling point, much less the ultra high temperatures that can cause the oxygen/hydrogen bond to break resulting in water burning as two gases.
Lead does not have to volitalize or oxydise in order to form a vapor, "vapor" is not the same as a gaseous product of combustion.
The term "vaporize" is an imprecise term, subject to mis interpretation.

Its greatly dependent on pressure as well as temperatures.


A vapor (American spelling) or vapour (see spelling differences) is a substance in the gas phase at a temperature lower than its critical point.[1] This means that the vapor can be condensed to a liquid or to a solid by increasing its pressure without reducing the temperature.

For example, water has a critical temperature of 374 °C (647 K), which is the highest temperature at which liquid water can exist. In the atmosphere at ordinary temperatures, therefore, gaseous water (known as water vapor) will condense to liquid if its partial pressure is increased sufficiently.

A vapor may co-exist with a liquid (or solid). When this is true, the two phases will be in equilibrium, and the gas pressure will equal the equilibrium vapor pressure of the liquid (or solid).[

And the differences in pressures are very great during the stages between ignition and the bullet leaving the muzzle.

[303Guy]

Thanks for all the interesting bits of information, Multigunner. (Thermocouples are that old?!!)


The microscopic pits , visible only as a darkened surface held just enough lube to prevent or lessen metal to metal contact.
Brightly polished bores caused more friction not less as we would expect. Same principle as the crosshatch honing of automobile engine cylinders to hold lube during the firing stroke.

http://i388.photobucket.com/albums/oo327/303Guy/th_MVC-463F.jpg?t=1262551516

These 'microscopic' pits seem to hold lube very well. This bore gets no copper fouling at all! (It just doesn't seem to like plain cast or paper patched boolits). The j-words do get a dose of 'waxy-lube' before seating. The rifle is accurate too.

[Multigunner]

Thanks for all the interesting bits of information, Multigunner. (Thermocouples are that old?!!)



http://i388.photobucket.com/albums/oo327/303Guy/th_MVC-463F.jpg?t=1262551516

These 'microscopic' pits seem to hold lube very well. This bore gets no copper fouling at all! (It just doesn't seem to like plain cast or paper patched boolits). The j-words do get a dose of 'waxy-lube' before seating. The rifle is accurate too.

From what I can see that bore is a bit past what I'd consider properly seasoned.
The surface isn't exactly rough in the same way as it would be if pitting had sharpe edges , its more rippled.
Some custom barrel makers have developed their own method of surface finishing of the bore to reduce friction on bullet jackets, the effect is much the same as the bore section you show here.
The problem of lubes with J-word bullets comes from the much higher pressures and velocity of most centerfire jacketed bullet loads. Lubes loose lubricity under great pressures, some more quickly than others.
There was a .30-40 Krag match grade bullet that had both jacket and lube grooves. They found this bullet worked very well, but that it worked better if no lube was used. The groove without lube reduced surface area in contact with the bore so friction was lessened.
The sealant groove near the base of the early milspec .303 FMJ bullets, the point where the stake crimp is applied, held a "beeswax" sealant/lube that would have had very little actual lubrication properties at those temperatures and pressures, but may have reduced friction by reducing surface contact. It also served to reduce possibility of core blow through by gripping the core firmly near the base.
Some solid bronze alloy bullets have grooves that look like lube grooves of lead bullets but these are there to reduce surface contact friction to reduce pressures and reduce bullet heating as well. No core to blow through, but less heat would mean reduced metal fouling and other beneficial effects.

Most metal objects begin to lose structural strength at relatively low levels of heating. Titanium's major benefit in use for supersonic aircraft is that it does not lose structural strength at high temperatures.

The forces at work on a bullet are awesome, G-forces of acceleration are terrific, pressures and shock of acceleration compress and deform metals producing heat on their own besides the heat transfered by propellent gases and friction.


PS
In case I didn't get the point across about Vaporization. If water had to reach the boiling point to become a vapor there would be no moisture in the air and no clouds.

[303Guy]

That bore had been fire-lapped before I cut the tip off. It is a little past what would be considered 'textured'.:roll: The lube I use is applied by dipping the bullet base into molten 'waxy-lube' where a cup of lube remains on the base and chamfer when seated. The purpose is actually to deposit a protective coating inside the 'suppressor-break'.

[BAGTIC]

Much of the barrel fouling that was common in the early days, before Cordite had the vaseline added, was due to the use of Cupro-nickel jackets and not connected to cordite use as it also affected rounds loaded with single-based powders.