Home Forums Hunting & Shooting Ask The Gunwriters Temperature of Fired Bullet

I just viewed a video of an SR-71 Blackbird spy plane. It stated the plane flew at 2,200 mph (Mach 3) and the surface temperature reached 1,000 degrees due to friction.

Has anyone ever determined the temperature of a high-velocity bullet when it reaches it's maximum speed? Years ago I remember reading that a .270 bullet rotates 180,000 rpm at it's maximum.

When you think of all the physical forces exerted on a fired bullet, it's amazing they can be so accurate and effective.

A bullet burns when it penetrates your body. So it is hot. How much I don't know.

From a 10 twist at 3100 fps, I think' it's faster than that. Anyone know the math?

Gotta be below the melting point of lead .

Friction applied steadily over a long period of time.

Think about passing your fingertip through a candle flame vs. holding it in the flame.

12/10x60x3100=223,200rpm

DT: Thanks!

Air friction yes. Barrel friction no.

Do not pick up bullets in the butts if you work back there.

I had a conversation with Bill Stegers one time about bullet design. He said that using HIGH speed photography Speer discovered that the bullet tip of exposed lead melted from air friction and that was one reason he used a no lead exposed design for his Bitteroots. That may explain some of why BC changes as the bullet goes down range; the tips melt off.

So yes they do get HOT.

How do plastic tipped bullets make it downrange intact?

267 C or 513 F according to this study using an infara red camera on a 5.56 M16 projectile. This is under the melting point of lead if memory serves.

It appears that the bullet heats up from being squeezed through the bore by a cloud of super hot expanding gas and actually cools as it travels downrange.

Where is my prize?

www.flir.com/uploadedFiles/speeding-bullet.pdf

pure lead

Melting point, 600.61 K, 327.46 �C, 621.43 �F .....

Alloys would melt at a higher temperature,

Gotta love the internet!

Could be that a high intensity magnum might have a higher temperature than the 5.56 bullet. However in the fractions of a second we are talking about the surface heat would be unlikely to penetrate far.

Note that the bullets cooled as they moved away from the gun.

The melted-tip theory of ballistics turned out to be a myth, created by thge limitations of the photography of the day.

I have seen cores melt, at least partially, in varmint bullets on very hot days, when shot through barrels that are already smoking hot. Often the bullets will zig off in a new direction, and sometimes they even come apart in the air. If you shoot them at paper there'll often be whirls of melted lead around the bullet hole.

But those are relatively small bullets, with thin jackets and very soft lead cores. And it takes some pretty high velocity to do it. One day in Kansas when it was around 100-105 degrees, Ron Spomer and I were shooting prairie dogs with the then-new Winchester USA brand of ammo, with very thin-jacketed 45-grain hollow-points. Ron was shooting a .22-250 and I was shooting a .223, and every time his barrel got REALLY hot the rifle started spraying bullets, while my .223 kept shooting very well. Turned out the cores were melting in the .22-250.

I have seen what looked like a melted swirl of lead from a .220 Swift. This is different from a trace or air disturbance as the bullet goes through the air.

i would think the plastic tipped bullets would have a lot less friction with the air than a more blunt lead tip. so they would build up less heat, yes?

Exactly.

I picked up a spent 270 grain hornady I'd just fired from my .375 H&H and it burned the [bleep] out of my fingertips. I won't forget that any time soon.

Tom

I believe I read some reports where the length of the barrel can affect the temperature of the bullet. I think a 500 degree bullet has some bearing on its performance when it strikes the target too.

I'll bet that a round fire with a sabot will have slightly different characteristics that a normally engraved bullet. I am not gonna be the one holding the infrared thermo gun trying to measure those suckers as they go by though!!!

They use a high temperature plastic in the point. Remember that the SR-71 had a saw-toothed leading edge that was filled with high temperature plastic that heated up pretty high, but did not deform. The saws tooth leading edge was designed to reflect and minimize incoming radar signals.

Depends on the alloys and the amounts.

Lead - Pb
Tin - Sn
Antimony - Sb

All Pb/Sn compositions have melting temperatures less then pure lead.

All Pb/Sb with Sb<~20% have melting temps less than pure Pb.

All Pb/Sn/Sb with Sb<~20% have melting temps less than pure Pb.

The more Sn, the more Sb you can add to keep it under the melting temp of pure Pb.

53% Pb, 20% Sn, 27% Sb melts about the same as pure Pb.

While that's correct, it's also irrelevant as a bullet doesn't travel for an entire minute.

A 12 twist barrel rotates a bullet one time every foot of forward travel it goes, regardless of the forward velocity. This probably diminishes as it slows down, but not a whole lot.

I had a 357 Harret and 110 gr hollow point pistol bullets would come apart and leave scrapnel holes in the target at 25 yds. what caused that??

The linear velocity of the bullet decays faster than the angular velocity. So as it gets farther downrange the spin will increase per linear foot traveled, rather than diminish.

I stand corrected...Thank-you

To convert muzzle velocity in fps into miles oer hour take muzzle velocity x60 x60 and divide by 5280. For example 850 [fps]x60=51000.51000x60=3060000. divide this by 5280=579.54 mph.

Just now reading this thread but I know first hand that this accessment is right on the money...A good friend of mine who was a "Spooky" crew member on our sister ship took an almost spent round in the right butt cheek as it passed through the thin skin of the aircraft.It was an AK round and he said it not only hurt but felt like he had been stuck with a hot poker..he survived of course but there's no doubt in my mind that it puts fire in the hole!!

Why don't we see burning targets or burnt hair on the game we shoot? I read that the advantage of the plastic tips was that they didn't burn off in flight as do lead tips. Think I will call that BS. Easy test- light a candle and hold a ballistic tip in the flame, gone in seconds. Now try it with a lead tipped bullet. You will drop the bullet before the lead melts.Rick.

because the 500 degrees is only touching the hair or targets for a thousandth of a second.

Doesn't need to travel for a whole minute to report its speed as rpm, just as I can drive 60mph without driving for a whole hour. In fact a police officer could give you a ticket for driving 60mph for just a few seconds.

My father took machine gun rounds through the stomach, bicep, and hand. He said there was no burning sensation at all.

Good possibility if they were through and through...my friends round stayed put in his azz and didn't go any farther,about 3" of penetration and I don't doubt his word!!!

If it's really hot, looks like it would start fires in grass, which it won't.

I suppose the perception of how a bullet in the azz feels could vary.

Can't figure why some of you guys are having a hard time believing this..of course they won't start fires...example: take a butter knife put it on the burner of a stove for several seconds then touch your arm and hold it there..a blister for sure.Then do the same even for a bit longer and quickly set it in "dry grass" Fire?? doubt it!! I think the problem here is the interpretation of the amount of heat generated vs time of flight.

Last year my guide told me that a .308 cal bullet leaves holes in game that are smaller than a 7mm. He explained that due to friction, the bullets diminish in diameter before they get to the target.

I guess you don't need to be a rocket scientist to be a licensed guide.

(No offense meant to anyone here)

shhh don't let the military that they don't need incindarys, just plain old bullets will get er done. "Throw some more hot lead at them there critters, Yosemite"

What pain you feel from a puncture wound depends on which pain receptors are damaged. Some people report knife wounds to be hot.

Your 357 pistol bullet broke up because most pistol bullets have very thin jackets, most rifling in pistols is very shallow, its easy for the deeper rifling to engrave the jacket and break it.

It you are shooting 300 yds, and the or 900 ft. and your twist rate is 1 in 12 the bullet will only rotate 900 times, the calculated rpm figure has no relevance.

If you have ever cast a lot of bullets you will know that sometimes fissure lines are produced length wise if the allow isn't ready, when shot the bullets appears to explode, drawn wire used in cup and extruded bullets can do the same thing giving the appearance of "vaporizing". The bullet is somewhat protected by the shock wave front, which is why rain drops don't affect the flight. (or by using the other reasoning bullets would be colder when shot in the raing or snow).

If anything a bullet can get shorter, especially when fired as the moment of inertia of the back part is over come before the front part, and a density packing occurs.

That's what I was going to say...and it also makes a difference if you take the bullet's temperature orally or anally.

Yeah.

Not that it's important, but it will rotate more than 900 times. The linear velocity decays faster than the angular velocity.

I have picked up intact SP bullets on a number of occasions after firing them across smooth, flat snow covered sea ice. The bullets do not melt into the ice but lay just under the surface of the snow generally. And they get a light coat of crusted snow due to being slightly warmer than freezing but quickly cooling upon stopping. I don't buy the melted core idea (though there is enough heat right around the jacket when the lands press into the jacket to momentarily melt streaks of lead under the jacket.)

Even an ambient temp bullet would produce enough friction in the brief time it takes to push through flesh to feel hot. I suspect the heat of the bullet increases as it expands inside of flesh and bone. Even so, I have yet to recover a bullet in meat which had the slightest evidence of being even remotely cooked.

This is not correct, it has the relevance of being the correct rotation rate. A rate is per time, not per distance and has nothing to do with the total number of rotations before impact.

One example of its relevance would be in the calculation of rotational forces at the jacket of the bullet.

Such forces would be much higher on a bullet of a given diameter fired at 3,000 ft/s versus 800 ft/s, for instance.

Yes and the sun also rises-- its not relevant within the context of the question- does rotational kinematics effect bullet segmentation? No doubt that many algebraic relationships exist, and if the stated figure were meaningful to a model relating the two but it doesn't. The time and space constants can be ignored in calculating other larger forces at work. Since were on if's-- if the flight time was 1/60 of a sec. the rotation would be 5400 rps, and for 1 min. the rpm would be around 300000. Ee know the axioms of distributive algebras still work.

The infinitesimal duration of a bullet's flight is nothing compared to the long duration of the SR-71's flight. Surely, the friction of flight takes a while to heat the moving object. How much heat can friction with air impart to a bullet within at most a couple of seconds?

So true, and to add to that a bullet is not an airfoil, it does not fly, it is projected.

This thread makes my head hurt

Interesting tho...

It is not true that a bullet with a 1-12" twist will rotate one turn per foot of travel regardless of forward speed. A bullet's forward feet per second decreases rapidly due to air friction, but its rotational speed hardly decreases at all. Therefore, as its forward speed decreases, it will spin more than one turn per foot of travel even though its rpm remains the same. If it were somehow to come to a dead stop in midair, it would still be spinning at that same incredible rpm.

Wow! I've stirred up some very interesting hornets' nests with my question. Here's another one:

Let's say I've reloaded two .30 caliber cartridges to fire in the same rifle. All the components are the same except for the powder charges. (The rifle has a 1-in-12 twist rate.)

The first cartridge will fire the bullet at 1,800 fps. The second cartridge will fire the bullet at 3,000 fps.

Okay, since the rifle has a 1-in-12 twist, are both bullets only turning once every twelve inches? To me it seems the faster the bullet is expelled the more momentum and more rpm's the bullet would have once it leaves the barrel.

I've got to lay down and put an icepack on my head now!

It is not true that a bullet with a 1-12" twist will rotate one turn per foot of travel regardless of forward speed. A bullet's forward feet per second decreases rapidly due to air friction, but its rotational speed hardly decreases at all

That is correct, but only noticably at extended ranges, also the the rate of spin slows slightly if you want complete info. although the differential rate of change is significantly less. the point was to put the forward amount of travel in perspective to the rotation. The stated rpm figures give the illusion the bullet comes out of the barrel spinning at some incredible rate. If you recall several years ago some of the ads for some bullets were advertising a buzz saw effect which made their bullets better. The amount of force generated by the spinning is also related to the dia. of the bullet.

yes, but the faster velocity will have a shorter time frame.

That's what he just said. I believe you are trying to correct the man by repeating him, a silly-sounding method of achieving something......

Old smooth bore projectiles would get really, really hot, because of the devils riding them.

That's why they invented spin, so the devils could not hang on.

Trying to summarize more than anything. No way all the factors are going to portrayed in an internet forum. Was hoping that someone would point out the obvious however- the equations involving rotation spin don't have enough information in them to conclude anything about bullets melting in flight. Also was hoping a lurking reading familiar with artillery would add a few comments on shell thickness vs. diameter etc. I'm sure the military has all kinds of "rules of thumb" on this stuff.

There was a thread a few weeks ago that went into detail about what causes a barrel to get hot.

I thought it was friction from the bullet going down the barrel, but some other readers gave good evidence that the barrel heat was from the burning powder.

However, does the friction of the bullet going through the barrel cause the bullet to heat up? I don't know, but would guess yes it does. The hot powder gasses acting on the base of the bullet would have some effect, but I don't know how much. For the short amount of time in the barrel, I doubt if the gasses would produce much heat the entire length of the bullet.

A far as which bullets would be most likely to melt, my only experience has been with a .220 Swift at about 4000 FPS, and with one particular bullet. No other brand of bullets left the puff of smokey looking tail as the bullet went down range.

So, I would conclude that for the core to melt, it would have to be with a fast bullet, in the range of 4000 FPS or so. Bearing surface would have some effect on how much and how quickly the bullet heated. The alloy of the core would have an affect on the melting of it. Then, like in my Swift, some bullets might melt and some might not.

Smoothness, or roughness of the bore might have some effect on the amount of friction and heat produced.

If you know the muzzle velocity and rate of twist, rpm is easy to figure out. Actually, it would be rate per minute, as the bullet is not in flight for a full minute. So is surface feet per minute easy to figure if you know the spin rate and the diameter of the bullet.

No, revolutions per minute is already a rate.

Maybe a really fast solid bullet (so it didn't explode on contact) could cook a rabbit when you shoot it.

Simply look at the heat required to melt a bullet and the amount of heat in a given amount of powder. Considering the energy available is inadequate to melt the bullet and then realize the total transfer of (heat) energy from the powder to bullet is extremely inefficient... There is absolutely no way the bullet can melt.
art

Reminds me of a thread a while back where some guys were saying that bullets actually melts holes in steel when shooting a steel plates.

Gotta love the seemingly "logical" explanations people contrive for things they can't get their heads around......and I think we all do one way or another. I still recall the first time I shot steel with a CF rifle (222 through a "tundra daisy"). (How does steel become liquid and resolidify so fast ? )

So are these fair to take away from this discussion?
* For a 1-12" twist the bullet will NEVER spin faster than the second foot of a 24" barrel?
* It spins at 100k's rpm (?) but will realistically never get close to spinning that many times?
* An average temperature of a given bullet is in the broad \ general range of 500 degrees F?
***Heat in the barrel comes mostly from the burnt gasses. To me this one seems to contradict other assumptions here about the minimal effects due to short duration - can anyone help me on this??? I am thinking perhaps friction plays more of a part than has been mentioned so far- just a thought. Guess comparing a moly bullet temp to a standard might be a good place to start. What else? Maybe how pressure plays into this perhaps???

Conclusion: bullet heat is not to worry about.

True
Probably more like 200K, but true about not likely spinning 200k; 3000-4000 Revs would generally be a lot.
This I doubt. Some small portions of the bullet, yes, but not overall or average temperature. I think this could be disproven mathematically though I'm not going to attempt it.



Is one part of the barrel hotter than another? If so, friction should favor more heat in the faster section of the barrel. (The muzzle end.) If the chamber end heats up more quickly (less likely due to the greater barrel mass typically) then one could assume the heat comes more from the burning powder.

kenjs1 - IF you/we were to shoot in semi auto or full auto, several rounds THEN the friction heat would ADD up. However you still have the HEAT from BURNED powder from every round fired.

kalik did a very good job stating options and even then more heat comes from powder BURNED.

I'm NOT being critical BUT I don't understand why it is so hard for some, others beside you, to accept the majority of HEAT comes from BURNED powder.

? Are y'all making it harder to understand than it is ?

You are trying to oversimplify though. Burned powder heat has just a tiny percentage of the surface area of the bullet to work on and the heat transfer rate through the bullet is quite slow. Small portions of a second is not enough to transfer any subtantive quantity of energy, period.

Fact is there are only two sources of heat; primers and powder. That heat is converted to pressure which is then converted to heat through friction from the barrel. The surface area of the bullet/bore contact is far larger than the bullet base and far more likely to transfer powder energy to projectile heat.

Combustion heat on the bullet base is intense, but too brief to be meaningful in the grand scheme...

If anyone doubts where the majority of the heat buildup of a barrel comes from, have a friend fire an M1 Garand and catch the fired case in your hands!!!
__________
NRA Life,Endowment,Patron or Benefactor since '72.

That's a good point also, and the more massive chamber end of the barrel does heat up first (or faster) than the muzzle end, another indication that powder is creating heat. Also, anyone who has fired cast bullets in a 45-70, especially those of modest velocity, will understand that they, though they may be run at speeds very similar to the 22 LR, will heat up the barrel much more quickly than will a 22 LR. Even when you consider extra barrel mass of the 22 rimfire, it still isn't the friction that's making the heat. The lightest loads in a 45-70 burn a lot more powder (make more energy) than the heaviest 22 rimfire loads.

And yet we have FMJs with lead open bases and Gas checks invented for hardcasts.

Is or isn't?

Nav & Kilk - ahhh great points thanks. I probably do make it harder than it has to be but still glad I asked . Reminds me of a long discussion I had with a friend convined that bullets just had to be slower coming out of a semi auto. Thanks for some really good responses.

kensj1 - I have chronod semi autos w/ same ammo fired in bolt
actions.

Those I chronod. WERE SLOWER than from bolt actions.

Makes sense to me; some of gas pressure is bled off behind the
bullet to operate the action.

Not theoretical discussion. Chrono told the story I M E.

I told my friend if it might be more noticeable in a recoil operated semi auto than a gas. One person responded with several test results of his own and while there were differences they were within the standard deviation of a given load. So while there is a difference it isn't worth worrying about. Least that is what that test showed.

Kenjs1 - yes, I didn't mean to imply the semi auto loads were 100 fps slower.
I compared these before '95 & the 742 was a friend's.

Therefore I didn't keep a record of the exact diff. IIRC ? the diff. was @60 fps.
You are correct, the diff. wasn't terrific but the semi auto WAS slower using
the same loads at the same time.

At that time I was fanatical about getting ALL the vel. I could get. The loads
were NOT above the loading manual's max. Again IIRC it was 52 grs of
IMR 4895 w/150 HSP.

Thanks for your reply. Jerry

I caught an M1 Garand case on the inside of my forearm when it got into my shooting coat through the zipper at the elbow. I still have the scar to prove how hot it was. 2nd degree burns hurt!

That didn't come from friction, and the short time the case was in the chamber didn't keep it from absorbing a lot of heat from the burnt powder. Why would the barrel be any different?

Fast Ed

Fast Ed - That's the way I see it too.

thanks Jwall. This was an interesting thread. I wonder how many psi is required to cycle the bolt on that 742?

Temp?

Damned hot.

kenjs1 - w/o knowing the operating pressure of those loads it would be impossible to determine.

SPECULATION - I 'had' a hypothesis based upon 'supposed' figures

BUT I decided it's better to just not guess. Jerry