lysanderxiii
Member
The same way the lead survives. The burn time is about 2 milliseconds. Ever do the bar trick of running your finger through a candle flame?
https://www.youtube.com/watch?v=vmv7EnTVtPQ
Projectile/Bullet Tempreture at what FPS?
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https://www.youtube.com/watch?v=vmv7EnTVtPQ
lysanderxiii
Member
Abrasion is why there is lead fouling, same reason there is copper fouling.
Gas check are used to... well... to check gas flow.
The high pressure propellant gas will escape past the bullet in the less sealed groove, causing gas cutting, which increases lead deposits in the barrel and can unbalance the bullet.
lysanderxiii
Member
They for got one other reason thin jackets fail....
A rough throat/bore in long barrels produce heat, causing bullets to fail. To much RPM adds to it. Berger bullet failure test. Infared images- core melting. http://benchrest.com/showthread.php?49336-Berger-bullet-failure-test And yes, i have had a spitzer nose melt out of a 243win. because of barrel conditions. Lead smears on the target, like in the photo. (not mine)
The engraving of the rifling does two things, it creates thin spots in the jacket and it creates stress concentrations in the corners of the engraving.
As the RPMs increase, the stress on the jacket increases and eventually the jacket will fail along the engraving lines.
A jacket after being engraved by the rifling will look something like this. You can see where it thins out, it is about 75% thinner at the corners.
J-Bar
Member
My question about gas checks was rhetorical; I know what gas checks are designed to do.
My first post was simply to point out that the hot, high pressure gasses behind a cast lead bullet (not talking about any jacketed bullets here) can melt some of the lead off the bullet even though contact time is very short. You apparently agree with that by noting that gas cutting can occur, resulting in lead deposition in a barrel. Gas cutting by a bullet works just like an acetylene cutting torch on steel...some of the metal is melted.
Gas cutting is likely to be the source of barrel leading when the cast lead bullet is too small for the bore; more likely than abrasion since the bullet is too small to begin with.
jmorris
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With an Oxy/Act torch you can't just set the flame throw the torch on metal and start cutting you do have to preheat the metal before you can cut it, onece the cut is started your operating around 7,000 degrees F.
Not like a plasma where you just hit the button and go, at closer to 20,000 degrees F.
J-Bar
Member
Perhaps the acetylene torch was a poor analogy...
Are you saying that hot gasses cannot melt lead off a bullet?
Are you saying that hot gasses cannot melt lead off a bullet?
denton
Member
According to IR tests done by the engineers at Lake City Army Ammunition Plant, whom I had the great pleasure of assisting in solving M855 failure problems.
The Berger photos posted win243xb demonstrate the failure mode very well. The lead melts, the side of the jacket splits, and molten lead is spun out of the jacket. I have produced exactly the same lead swirl pattern as shown in the Berger image with my 223. I have also seen the bullet jackets of the Berger bullets.... split jacket, core gone, tiny bits of lead that had melted still clinging to the inside.
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barnbwt
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The friction of the bore is one contributor. The distortion of the bullet in the bore is another. Both of these involve the bulk mass of the bullet, though, and would take some time to conduct all the way out to the bullet tip (we're talking seconds/fractions of a second, here). Actual friction with the air is probably a smaller contributor than you think; there is a lot of movement over, but a lot of convection carrying heat away at the same time, and there is a painfully small surface area in contact with the stream (and it is both behind the shockwave, and a good portion lies on the trailing side; both these factors reduce the velocity at/near the surface greatly)
One that has not been mentioned, but which I think would most directly contribute to tip melting down range, is air compression. The shockwave initiated at the tip of a supersonic body is essentially a molecular traffic jam; the momentum of the molecules won't let them shift out of eachothers' way to accommodate the body passing through, so they stack up against eachother in a denser pattern to let it through. That denser pattern is 'compression,' and it results in an increase in temperature (the 'anger' of the 'drivers' in the 'traffic jam,' if you will
). Once inside the traffic jam, everything slows down, until the disturbance (stopped car/on ramp/etc) has passed and the condensed molecules can move back to the space left behind by the bullet. You 'shock up' and then 'shock down,' as an air molecule when the bullet passes. The first is when you abruptly slam your brakes as the car in front of you does the same, and the second is when that rubber-necking idiot finally passes the car-wreck and floors it back up to cruising speed & you follow suit. After the first, you might feel very 'heated,' and much relieved after the second to be on your way once more
Since the bullet is continually stacking up a cone-shaped wave of compressed air in front of itself, that heat being generated is getting conducted straight into the mass the whole time; it's basically surrounded by a bubble of air heated up hot enough to get to sonic speed (hot air has faster 'reaction time' so the molecules can shift out of the way without generating a shock wave). The curved, smooth profiles of bullets actually result in many smaller shocks ('fan' wave shocks) all along their surface, with pressure rising along them until the taper on the back side. Now, the air cools rapidly on the tapered slope when it 'shocks down' to a lower pressure, but the tail of spritzer bullets is so short that there won't be as much heat transfer.
Darker color is denser air. Shock up (at very high pressure), pass over the body at elevated temp/pressure, shock down back to normal(ish). The more pointed the tip & faster the speed, the more triangular the shock; the faster the speed, the sharper the angle of the shock (and fiercer the pressure gradient)
The result is that the very act of the bullet ramming through the air heats it quite a lot, just by flying supersonic, and it is most pronounced at the very tip of the body; right where that polymer usually is. So I can see how this can eventually become an issue if you drive a round fast enough. Heck, when you get above Mach 5 or so, the air & surface themselves start burning & reacting due to the heat and energy involved in these shockwaves, and above Mach 7 it's so bad the molecules begin breaking up into individual atoms & forming plasmas. By that point, things are booking fast enough that the air molecules are basically crashing into the surface to knock chunks loose (ablation) and your basically dealing with orbital re-entry type stuff.
This effect is why the Concorde had a crazy powerful air-conditioning system (I think the ambient air temp surrounding it was like 200-something degrees, if I'm remembering that college factoid correctly. Unlike a bullet, though, aircraft also have a massive surface area for their size that really does contribute a lot of skin friction) and why the Blackbird had to be skinned in that hideously-expensive titanium (and to accommodate thermal expansion at high speed, it was made so loose it leaked fuel from joints & fasteners on the ground when cool) and why the Navy's rail gun projectiles are made of tungsten (Mach 7, yo!) and glow brilliantly in flight (and why the armature rails of the gun are turned into plasma and destroyed after only a few shots)
I wonder if ceramic tipped bullets might be much more resilient to this effect in super-high speed chamberings. That's basically the approach taken by re-entry vehicles, after all (put something with very low heat transfer that's also tough enough to hold up to the high speed flow out front, so it takes the brunt of shocking the air, and doesn't transfer the heat back to the main body)
TCB
One that has not been mentioned, but which I think would most directly contribute to tip melting down range, is air compression. The shockwave initiated at the tip of a supersonic body is essentially a molecular traffic jam; the momentum of the molecules won't let them shift out of eachothers' way to accommodate the body passing through, so they stack up against eachother in a denser pattern to let it through. That denser pattern is 'compression,' and it results in an increase in temperature (the 'anger' of the 'drivers' in the 'traffic jam,' if you will
). Once inside the traffic jam, everything slows down, until the disturbance (stopped car/on ramp/etc) has passed and the condensed molecules can move back to the space left behind by the bullet. You 'shock up' and then 'shock down,' as an air molecule when the bullet passes. The first is when you abruptly slam your brakes as the car in front of you does the same, and the second is when that rubber-necking idiot finally passes the car-wreck and floors it back up to cruising speed & you follow suit. After the first, you might feel very 'heated,' and much relieved after the second to be on your way once more Since the bullet is continually stacking up a cone-shaped wave of compressed air in front of itself, that heat being generated is getting conducted straight into the mass the whole time; it's basically surrounded by a bubble of air heated up hot enough to get to sonic speed (hot air has faster 'reaction time' so the molecules can shift out of the way without generating a shock wave). The curved, smooth profiles of bullets actually result in many smaller shocks ('fan' wave shocks) all along their surface, with pressure rising along them until the taper on the back side. Now, the air cools rapidly on the tapered slope when it 'shocks down' to a lower pressure, but the tail of spritzer bullets is so short that there won't be as much heat transfer.
Darker color is denser air. Shock up (at very high pressure), pass over the body at elevated temp/pressure, shock down back to normal(ish). The more pointed the tip & faster the speed, the more triangular the shock; the faster the speed, the sharper the angle of the shock (and fiercer the pressure gradient)
The result is that the very act of the bullet ramming through the air heats it quite a lot, just by flying supersonic, and it is most pronounced at the very tip of the body; right where that polymer usually is. So I can see how this can eventually become an issue if you drive a round fast enough. Heck, when you get above Mach 5 or so, the air & surface themselves start burning & reacting due to the heat and energy involved in these shockwaves, and above Mach 7 it's so bad the molecules begin breaking up into individual atoms & forming plasmas. By that point, things are booking fast enough that the air molecules are basically crashing into the surface to knock chunks loose (ablation) and your basically dealing with orbital re-entry type stuff.
This effect is why the Concorde had a crazy powerful air-conditioning system (I think the ambient air temp surrounding it was like 200-something degrees, if I'm remembering that college factoid correctly
. Unlike a bullet, though, aircraft also have a massive surface area for their size that really does contribute a lot of skin friction) and why the Blackbird had to be skinned in that hideously-expensive titanium (and to accommodate thermal expansion at high speed, it was made so loose it leaked fuel from joints & fasteners on the ground when cool) and why the Navy's rail gun projectiles are made of tungsten (Mach 7, yo!) and glow brilliantly in flight (and why the armature rails of the gun are turned into plasma and destroyed after only a few shots)I wonder if ceramic tipped bullets might be much more resilient to this effect in super-high speed chamberings. That's basically the approach taken by re-entry vehicles, after all (put something with very low heat transfer that's also tough enough to hold up to the high speed flow out front, so it takes the brunt of shocking the air, and doesn't transfer the heat back to the main body)
TCB
243winxb
Member
Photos i posted were not from Berger Bullets. Berger has made changes to there bullets, to correct problems that were in the 2008 link, that i posted above. Eric Stecker became Company President in 2014.
denton
Member
Thanks for the clarification.
Yes, Berger did fix the problem. The new bullets have a thicker jacket and apparently perform well.
Yes, Berger did fix the problem. The new bullets have a thicker jacket and apparently perform well.
I know that this is an old thread, but I recently ran across some related information in a magazine article.
Lane Pearce, in a Shooting Times article (February 2016 issue) entitled Hornady's Hot Tip presented some information regarding bullet heating due to air friction.
This forced them to switch from Delrin (melting point of 400 degrees) to a more heat resistant polymer.
Apparently Mr. Pearce, in a former life, was an aerospace engineer and spent much of his career working on the Space Shuttle program so the topic held special interest for him.
At any rate, the information from the article agrees very well with what jmorris posted earlier in the thread.
Lane Pearce, in a Shooting Times article (February 2016 issue) entitled Hornady's Hot Tip presented some information regarding bullet heating due to air friction.
"Thermal modeling predicted bullets traveling at velocities over 2,100 fps see stagnation temperatures above 700 degrees Fahrenheit."
This forced them to switch from Delrin (melting point of 400 degrees) to a more heat resistant polymer.
Apparently Mr. Pearce, in a former life, was an aerospace engineer and spent much of his career working on the Space Shuttle program so the topic held special interest for him.
At any rate, the information from the article agrees very well with what jmorris posted earlier in the thread.
rcmodel
Member in memoriam
I'm still at a loss to understand how a .220 Swift plastic tip varmint bullet starting at 4,000 FPS remains supremely accurate at 400-500 yards.
But a .30 caliber target bullet starting at 3,000 FPS melts the tip off????
rc
But a .30 caliber target bullet starting at 3,000 FPS melts the tip off????
rc
It was actually much less extreme degradation than the tip completely melting off. What they saw was an (initially) unexplained increase in drag once the bullet traveled past 400 yards. The tip was deforming enough that the bullet was experiencing more drag than it should have at longer distances.
Accuracy shouldn't have been affected significantly because the spin should have insured that as the tip deformed, the deformation stayed fairly symmetric.
Accuracy shouldn't have been affected significantly because the spin should have insured that as the tip deformed, the deformation stayed fairly symmetric.
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