I have a question concerning a barrel getting hotter as it is shot numerous times:

Is it higher velocity that makes a barrel heat up quicker, or is it higher pressure that makes the heat?

I realize that they are almost directly correlated, but am wondering about using reduced loads to lower barrel heat while prairie dog shooting. I can reduce the pressure of a known load to get lower velocity, or I can use a different faster powder that creates continued high pressures but lowers the velocity. Which one will give me less heat?

My opinion is that it is the friction of the bullet passing through the barrel that causes the heat.

There might be some heat generated by the hot powder gasses, but I think most of comes from the bullet's travel through the barrel. Lower velocity would probably prevent the barrel from heating up as quickly as high velocity.

But, I don't see where a slow or fast powder would make all that much of a difference, if the velocity stayed constant.

You don't necessarily want to reduce a slow burning powder to get low velocities. Consult a loading manual and use a powder suitable for the velocities you are looking for. Also be careful and don't use too much of the fast powder.

All the heat comes from the powder. No question about it. It's as simple as that.

The friction drains energy � it does not produce it.

The powder � slightly assisted by the primer � is the sole source of energy in a nonrocket cartridge. Several things drain it (friction, recoil, noise, etc) leaving only about 25�30% propelling the bullet.

Where else would cartridge energy come from?

Let a hot summer sun heat an idle rifle with a loaded round in the chamber, and it'll still be the heated powder that expends its energy when you pull the trigger.

We talk about (and measure) pressures, but it's the heat that's associated with those pressures that makes the barrel hot.

If you want to amuse yourself with intuiting some phenomena of interior ballistics, tune your noodle to this �

A pressure-cooker in your kitchen can produce some down-right nasty havoc if for some reason it lets go at or near its normal operating pressure of 20�30 lb/sq in. Try comparing that with a high-velocity cartridge operating at something like 60,000 lb/sq in.

That's interesting as hell. I would have thought the friction caused the heat as well.

Friction can certainly convert mechanical energy to heat.

I think it is both of the heat produced by combustion of the powder and the friction of the bullet moving down the barrel. Combustion of the powder produces both heat and kinetic engery of the moving bullet and gases. The friction in the barrel converts some of the kinetic energy to heat. What the balance is between these two sources of heat is I have no idea.



Whether using a bullet with a short bearing surface and mild charges of a faster burning powder would make much of practical difference I couldn't say.

Ken is correct.

Pressure and heat are manifestations of the same microscopic thing: molecules in motion. The hotter they are, the faster they move and the more force they exert on their surroundings.

Consider that propellant gas peaks at 2,000 degrees or more, and I think you'll soon find where the barrel heat comes from. It's the same mechanism that makes a car engine hot.

Friction contributes little to barrel temperature.

I've actually shot coated XLC's and uncoated cup and core bullets from the same rifle (223WSSM), at the same velocity and measured the heat. The coated bullets produced far less heating on the barrel. From memory, three naked bullets produced about the same heat as five coated bullets.

Friction would seem to be the likely difference. FWIW, Dutch.

I wasn't arguing the percentage contribution. But Ken's statement wasn't clear as to how friction was stealing the powder's energy.

The force of friction in a barrel is around 150 pounds, more or less. Working over 2 feet of barrel, that's about 300 foot pounds.

In a 30-06, that's not the dominant source. In a 223, it's a greater proportion of the total but still not dominant.

OK. Let's look at that. (I wasn't trying to explain the obvious � just stating the facts, Ma'am.)

� The powder burns, converting latent energy into operating energy.

� That energy pushes the bullet forward.

� The moving bullet rubs against the sides of the bore.

� That rubbing � friction � produces heat.

� The barrel absorbs some of that heat (and the bullet gets some of it) as well as the greater heat that the combustion produces.

� The push that produces the movement that produces the rubbing produces some of the heat that the barrel absorbs.

� The heat that the barrel absorbs does not push the bullet.

� The heat that the barrel absorbs stays behind while the bullet goes wherever it's going.

� The heat is one expenditure of the powder's energy. The push is another. So not all the powder's energy is spent as push.


X-Y=<X.

Now please don't ask me to explicate the fundamental distinctions between British thermal units (Btu) and degrees Fahrenheit (�F)!

denton's number for bullet friction sounds familiar. Going through the math, you get a temperature rise of about 1 F from the bullet's friction. The rest of -- the bulk of -- the barrel heating comes from the gases. The heat transfer comes from convection (molecules banging on the metal) and radiation (light absorbed by the metal).

To reduce the temperature of the gases, reduce the pressure.

Coated bullets need less pressure to make the same velocity, so the gas temperature will be lower.

Stretch a rubber balloon a bunch of times and feel it... bend wire back and forth repeatedly in the same spot, and then feel it.

Barrels also swell slightly in an advancing wave trailing the bullet. There is a bit of internal friction there which is still sourced from the burning powder's energy, but not due to bullet/barrel friction.

The venting gas, post exit, cools significantly (Joule-Thomson effect) through expansion and stays in the barrel far longer than bullet transit time.

2525
Suspect you used convection where you meant conduction...
art

The latent energy of smokeless powder is, IIRC, about 175�180 foot-pounds per grain. If all the energy from fifty grains at 175 ft-lb/gr were expended on propulsion alone, the kinetic energy of the bullet would be between 8,000 and 9,000 ft-lb (8,750, according to my creaky math, bleary eye, and dull pencil).

(IIRC, the figure is about 178 ft-lb/gr for the IMR powders. But I'm 'way too tard and sleepy to look it up.)

Ken, I hope you're simply tir'd and not actually going "tard" at this point.

So bottom line is: if I reduce the pressure, it will thereby reduce the heat going into the barrel?

Yessir. This is why hot loads lead to shortened barrel life

Yep. PV=NRT. All things equal higher pressure is directly correlated to higher temps.

Bullet friction heating is immediate--whatever the amount, it dumps the heat right into the barrel steel. Hot gasses heat via convection and radiation. Radiation is fast, whereas convection is slow.

Radiation heat transfer depends greatly on the temp., and given the very high temp. and the very short times involved, it's almost certain the hot gas heats via radiation.

It can also be argued that friction frequently decreases with higher rubbing speeds, so my vote is barrel heating is largely via radiation from the hot gas.

Too bad we can't include jpegs in the posts. I have some rather interesting photos of just how fast pure radiation can heat heavy steel cables up and vaporize them in well under a thousandth of a second.

Pour some powder out on the ground. Light it with a match and hold your hand over it.Then take a bullet and rub it like hell on a piece of steel and hold that steel with your hand.
See which burns you the most.

I agree that the burning powder contributes most of the heat, but friction does contribute something (even a little) - just clasp you hands together tightly and rub them together fast. Even rubbing once will generate some surface heat that adds to the barrel temperature.

the copper of the bullet will absorb more heat from friction than the barrel steel. but all that is of such a low value, its the hot gas that produces barrel heat, pressure is the resistance to flow of the hot gas produced by burning the powder.

How hot does an air rifle get from friction heat?

Interesting question!

Different ball park, different league, different game �

Compressed air cools when it's suddenly released and expands.

May have something to do with why quality air-rifle barrels are bronze or brass, not steel!

Something to scratch the ol' noggin about, isn't it?

Next question � Does that cooling absorb the heat of the pellet-barrel friction?

I'll never tell!

So, to apply this to a real scenario:

If I load a 22-250 and a 223 to 3200fps, the 22-250 will actually create less heat since it took a lower pressure to accomplish the same velocity?

PS--I have a vague recollection (sorry Ken) of a 220 Howell developed with the same principle in mind.

Well, it has been 30 years (!) since I had thermo class, but I recall convective heat transfer implies the motion of the gases is contributing to the transfer; the greater the churning (velocity) of the fluid, the greater the heat transfer. Conductive heat transfer is usually between metals in contact.

I believe convective heat transfer will be most of it. The molecules in the gas are incredibly energetic, and with the motion of the fluid, each molecule that dumps energy into the barrel is soon whisked aside by another fresh, hot molecule in the stream.

It's been a while since I read John Corner's book on internal ballistics, but I recall radiative transfer is about 1/4 of the total. The QuickLoad manual might include an estimate.

edit I'll quote the Wikipedia: Although often discussed as a third method of heat transfer, convective heat transfer actually describes the combined effects of conduction and fluid flow.

Fair enough.

An eloquent answer.



Not so.

If two otherwise identical objects are at the same temperature, and one has twice as much mass as the other, the one with the greater mass has twice the thermal energy.

The mass of the gas after combustion equals the mass of the powder before combustion. The 22-250 has a considerably larger mass of powder, hence more heat energy, all other factors equal.

Anybody who's shot various .22 caliber centerfires extensively should have noticed that sporter-weight barrels of:

1) A .22 Hornet firing a 40-grain bullet at 3000 fps...

2) A .221 Fireball shooting a 50-grain bullet at 3000 fps...

3) A .223 Remington shooting a 55-grain bullet at 3100 fps...

...will heat up at VERY different rates.

The friction of the bullets is a factor, since they have different bearing surfaces. But the big heat factor is the amount of powder being burned.

I know I've been burned by a piece of brass thrown out of rifle and that weren't because of the friction caused by it being tossed.

It seemed to me that so much heat transferred from a gas over milliseconds would be rather remarkable. Then the light bulb went on, the gas is quite dense at peak pressure. Don't discount conduction. Would be interesting to measure the temperature along a non-tapered barrel.

Yep. Amazing how hot a brass case is when jerked out before the heat can be transferred to the chamber. And there ain't no bullet friction involved.

I was going to do that with several cartridges, but first the great expense and then a stroke blew that plan all to Hell (and a few more hospital "vacations" followed).

I forget, now, where I was going to get the stick-on sensors and the recording software. I remember vividly that the cost made me gasp but don't remember the $$ range.

So I'm still curious. Had a bunch of intriguing and practical heat studies planned.

So Ken and all,

Shooting the same bullet.

Will a cartridge case holding 60 grains of slow powder (RS Magnum) at 50,00 psi have a longer barrel life
than the same case burning 50 grains of a moderate faster powder (RS Hunter) at 60,000 psi?

10 grains more 10,000 less psi
10 grains less 10,000 more psi

Which one will produce more heat?

Now we get to the question of whether by "heat" we're talking about Btu or �F or both.

A pine log shredded into excelsior and a kitchen match burn at about the same �F, but the excelsior produces a heck of a lot more Btu.

Light and heavy powder charges burning at different rates in vastly different combustion enclosures are hard to compare � impossible to compare simply. Intuition and country-boy logic offer no help at all.

If I win the lottery �

Ok, so back to my question. How about the same enclosure?

Funny, interesting, whatever...

I have been asking this question here at the campfire probably once a year and still no answer.

That's why I get the brass out of the chamber as quickly as possible. I don't know how much it really helps keep the barrel cool, but I feel better about it.

Lower peak pressure means longer barrel life � as I've explained here repeatedly, ad nauseam, for several years.

The larger charge produces more Btu than the smaller charge � at the lower peak pressure, the peak �F is lower than the temperature at the higher pressure.

Load a .30-06 to .30-30 or .30-40 maximum peak pressure, and your barrel will be accurate longer.

To intuit the significant difference between �F and Btu, heat a room now with propane, later with pi�on. The gas will have to be hot (�F) to put-out any Btu, and the pi�on will put-out a lot of cozy Btu at a much lower �F.

My grandparents in south Alabama used to "heat" each occupied room with butane. You'd have to huddle over the heater to keep your front warm while your back side turned blue. One night, I was leaning back in my chair, just barely warm enough to be comfortable, with my feet toward the gas heater. One boot caught fire. Out in the center of the room, you could see your breath. Lots of �F, not many Btu, rapid dissipation.

adiabatic heat pump according to Art Alphin's manual

I don't have any idea what it means

adiabatic � occurring without gain or loss of heat

Dr Howell
I have No. 599 of your book re Custom Cartridges. Do you have another available? When will we see the second volume? Thanks

No second volume. The ol' fa� � uh � fossil just can't do it.

Expect to hear soon that the first volume will again be available (but not from me). I gave the films to a friend, and he's reprinting it. I don't (and won't) have the capital.

I'll let everybody know, as soon as I hear.

I've designed a passel of cartridges since I did that book. May consider offering a collection of those drawings. Will also continue to design a few custom wildcats now 'n' then, if anybody wants me to.

"ad nauseam: Definition from Answers.com
ad nauseam adv. To a disgusting or ridiculous degree; to the point of nausea. [Latin ad , to + nauseam , accusative of nausea ,"

Ken, thank you!

SU35, you've asked two separate questions, and Ken has tried to explain that no single answer can cover both.



Yes, I think the lower pressure cartridge will give longer barrel life due to the lower gas temperatures. There may be more total gas at that lower temperature; however:



This one's not so easy. Ten gn more powder producing that much less pressure is likely not burning fully. Those bits of unburned powder represent heat not liberated flying out the barrel with little effect on heating the barrel beyond rubbing. All those lumps of unburned powder banging on the heated barrel throat could be erosive; I can't say for certain.

If all the powder yet manages to burn, there will be more gas but at a lower peak pressure and temperature. The total heat dump to the barrel is a combination of the total flow and the flow's temperature and pressure. It's not obvious to me how the combined effect will vary.

Also, a long burn will be releasing some heat down the barrel instead of all inside the chamber. This will spare the vulnerable throat some heating. The throat is the spot usually damaged. It sees the highest temperatures for the longest time.

Air guns-- significant amt. of heat is generated by an air gun. One can use the ideal gas law eq. (as stated earlier) pv= muRT to or pv/t=p'v'/t' show the algebraic relationship between the variables, or simply leave some oil in the barrel, shoot it and as it diesels conclude this as the gun falls apart.
The amt. of temperature differential between say two of the same wt. charges but different burning indexes is a funtion of mu in the above equation, the molar mass of the nitrates used in the propellant. As faster powders usually contain a higher ratio of nitro, the temperature will be higher. but for the grass roots guys use the same charge of 296 vs.231 in your 44 mag. and conclude this as the gun falls apart. (this can also be seen as a broader curve in the peak pressure curve if you have something like quikload, or Matlab and pressure equip).
The particles of heated material from the powder, (or corn cob if you forgot to shake the case out) don't simply rush out the end of the barrel (at least while the bullet is still in the barrel) the kinetic energy they transfer to a specific location on the barrel metal in available while the bullet is still in the barrel. Think plasma torch.
The amt. of energy from friction is insignificant compared to the other factors. Remember how it easy it was to get the bullet out with the cleaning rod when you forgot the powder and the primer pushed it half way down the barrel.
Barrel life, or more accurately lead life, or more accurately accuracy is caused by the cooling off of the barrel, and the cracking that occurs than the heat of the barrel, per se. Granted the barrel needs to be heated in order to cool off, but its good to map causality.

BTU and temperature are very different units. BTU is a measure of kinetic energy. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree fahrenheit. Temperature is a measure of a physical property of an object. It does not indicate the amount of kinetic energy or work that can be accomplished because temperature includes no measure of capacity.

A couple years ago I experimented with loads in my 45-70s using a few different powders. Medium velocity loads with Reloder7 powder didn't seem to heat-up the barrel much at all (and were extremely accurate, by the way). However, lower velocity loads with much lighter charges of XMP5744 powder seemed to heat-up the barrel much more quickly (higher temperature with fewer rounds fired). This seems to fly in the face of the idea that larger charges of powder, or hhigher chamber pressures, create higher barrel temperatures as a rule. A bit of checking revealed that 5744 contains a relatively high percentage of nitroglycerin as compared to Re7. I always wondered if that is the reason for the higher temperatures with 5744. Any insights?

The amt. of temperature differential between say two of the same wt. charges but different burning indexes is a funtion of mu in the above equation, the molar mass of the nitrates used in the propellant. As faster powders usually contain a higher ratio of nitro, the temperature will be higher. but for the grass roots guys use the same charge of 296 vs.231 in your 44 mag. and conclude this as the gun falls apart. (this can also be seen as a broader curve in the peak pressure curve if you have something like quikload, or Matlab and pressure equip).

A related issue regarding barrel heating due to friction came up with the adoption of the M249 LMG. The guns would develop unexpectedly wide dispersion as they heated up during testig at maximum sustained rates of fire. The problem was determined to be related to the "buttering" of the then lead core bullets. The bullet would be heated to the point where the core would get soft when the gun was fired at near maximum sustained rates of fire for extended periods of time.
I seem to remember a discussion of the measured internal barrel temps showing highest temps at the throat which generally decreased as you went towards the muzzle as you would expect in terms of time exposed to the high pressure gas. (The barrel steel near the muzzle is exposed to the hot gas for an extremely short period of time.)However, the temps began to climb again fairly dramatically towards the muzzle again due to the heat from the friction of the high velocity 5.56 bullets at high sustained rates of fire.
The cure for the buterig problem was adoption of the green tip, non-lead round for the 5.56.

For the record, DO NOT USE THE SAME CHARGE OF 231 POWDER VS. 296 POWDER IN YOUR 44 MAG! This will surely cause dangerous pressure, damage to the gun, and possible injury to the shooter, up to and including death. I know that Etoh didn't really mean to suggest that, but it seemed to me prudent to reiterate the point. There is an example of just such a mistake hanging on the wall at Jay's Sporting Goods. It used to be a Ruger Super Blackhawk. Now it is just twisted metal with major pieces missing.

Etoh; Did you allow for the energy to make the gun fall apart?

not sure what the question is redhead, my example was simply a statement on differences in molar content of nitro between two powders when compared on a wt. basis. The potential energy stored up as chemical energy in the form of the powder must be above the "burst" limits of the device regardless of the pressure. On my NFA weapons, prolonged periods of full auto and barrel muzzle temp. increase especially when using a suppressor are quite noticeable. However if you wish to include these in the discussion , we should bring in artillery also as the friction plays an even profounder role. Any "model" verbal or mathematical must be explained in the basic gas laws to be relevant or it becomes a series of testimonials.

How warm a barrel feels to the touch is not (necessarily) what causes barrel erosion. I could pass 250 F steam all day through a stainless barrel, and it wouldn't erode, but you certainly couldn't hold it in your hands.

To erode, the surface in the bore has to be brought to a high enough temperature and bombarded with gases and propellant particles. I simply don't know what combination of temperature, pressure, velocity, and duration are required. While the combination of temperature and pressure is a major component of the heat transfer to the throat, the total volume of gas passing by is also significant. In the example cited by SU35, the temperature will be much lower, but the volume is (perhaps) higher.

As you noted, it's not just grains of powder that count; the energy per grain is important. Also important is how the burn progresses. A slow, low pressure burn leaves more energy in the gases. The slower burn will also leave the barrel corked longer by the bullet, so while the peak gas temperature might be lower, the total heat transfer to the barrel could be more. Again, I don't have enough numbers to help here. A full 3D simulation of the problem is probably the best way to learn, but only the Army is running those.

All by-products of internal combustion Heat, pressure, friction but no need to make it any more complicated than it is

one left out force here is torque. It's more informative to do this problem in units of work, How much work does it take to heat a barrel to, so, and so, how much work is created by the torque. you could do a finite element analysis on the problem easily in matlab, but as stated -- if its that important someone has to pay.
each time the barrel cools down from the heat the cracking differences in cooling increases the surface area open to erosion by the next shot.

Original question wasn't a request for anyone to do an energy balance...

Most of this has been touched on already, but...here are the ways heat energy enters barrel steel during a shot:

1. Bullet passage down bore: heat energy into barrel equals part of the friction force times distance travelled (bullet gets some too, but I don't know if it's exactly half/half).

2. Not-quite-elastic springback of barrel steel after barrel dimensions change ever-so-slightly in response to containing tens of thousands of PSI. The stress and resulting strain developed in the barrel steel can be calculated, and I presume there's some factor out there to account for damping/energy loss in springback. Can't remember offhand.

3. Convection between hot combustion products and barrel insides.

4. This one is out there a bit - if you're flowing fluid through a conduit, there is friction between the flowing media and the conduit. That means that pressure energy in the flow is dissipating as heat either in the flowing media or the conduit. I'd bet both.

the op question was answered with the poster that gave the pv/t=p'v'/t' equation. the relationship is linear, after that it was thrown out to open discussion

the amt. of friction is really small compared to the other forces, if a primer can push the bullet half way into a barrel,no where close to half and half. the heat erosion at the base of the bullet will cause "buttering" if the base is soft enough.(cast bullets at higher velocities).
#4 isn't that far out. Rheology physics usually assigns a viscosity constant to the fluid however, in this case it would be difficult.

It's a good question, because you have two effects operating at the same time, one pulling one way and the other pulling the other. It's probably difficult to determine without experimentation, and it's a lengthy experiment. I doubt anyone is going to give a numerically correct answer from first principles.

PV=NRT only works for an ideal gas. The gas in the barrel of a gun is far from ideal. Even pure Nitrogen is non-ideal, because it comes in two-atom molecules. However, the pressure/volume/temperature ratios still work.

The passage of the bullet down the barrel is not quite an adiabatic process. A cold barrel will "rob" more energy out of the propulsion gas than a hot one does, because heat transfer is proportional to temperature difference, and there is less temperature difference between a hot barrel and the hot gas. The dominant reason guns shoot faster in hot weather is that the barrel is hotter and steals less propulsion energy. Temperature of the ammunition is a secondary effect. It has practically nothing to do with the initial temperature of the powder. It's mainly steel, brass, and lead absorbing heat from the gas.

and an oxy acetylene flame is around 6000 degrees F.

apply the flame of a torch to a barrel for 10 seconds and you will not have a barrel as hot as one shot 3 times in the same time period...
exposure to 2000 deg temps for extremely short periods cannot adequately explain, in my mind, the process of barrel heating...

friction seems like a much more likely source...
and mathman is correct... friction can convert mechanical energy into heat... and in very short order...

FWIW, here's another easy-to-see example of the crucial distinction between the nature of heat (�F) and the volume of heat (Btu) �

� two birthday cakes � one for a one-year-old, the other for any eighty-year-old �
� one with one candle, one with eighty candles (all candles, on both cakes, as nearly identical as possible)
� Every candle burns at the same flame temperature (�F).
� The air above the eighty-candle cake is eighty times as hot (Btu) as the air above the one-candle cake.

I've had several cheap electric heaters that got very hot (�F) and would put-out only 1,500 Btu.

I have one now that doesn't get as hot (lower �F) but puts-out 2,300 Btu.

(Different technologies)

while the gas laws are for mostly ideal conditions, they none the less give a good start. No math model will include everything, but each different one can give a different picture for understanding. Just using the ideal, work, and a little calculus will give some pretty good measurements. Taking the area of the bore x pressure (converted) to get the force, then integrating for work, then conversion to velocity will account for abut 98-99% of the work done in the system when compared against the readings when chronoed. Again using the pv equation and using the volume of the bore the muzzle pressure and exit velocity can be caluculated. In any event the curve is almost flat after the first 12 inches, indicating little acceleration (almost constant velocity) and obviously because its always hotter towards the chamber. The amt. of work engraving the bullet from the rifling's far exceeds the heat generated by friction. Not only does the zinc in the gilding metal act as a lubricant, but the metal and the residue from the last firing, along with small amts. of oil that were polymerized to varnishes and lacquers. There is little doubt friction causes heat build up, look at your auto engine, but the coefficient of friction for the bullet when compared to the other forces can be ignored to linearize the solution.
As far as the question the op asks, the barrel heat increase between a 204 and a swift shooting the same velocity and pressure is do to the increase in propellant wt. alone.

The numbers just don't add up. The highest reported bullet drag force I've seen was in an Army report claiming 400 lb for a .30 conventional bullet (original X bullets were much higher). Over a 2 ft barrel, that's 800 ft-lb total drag energy which works out to 1 BTU.

A 3 lb barrel needs about .36 BTU for each 1 F of temperature, so we're looking at a 3 F rise from bullet drag, and that's the worst case numbers I could find--and it assumes all the friction heat goes to the barrel with none to the bullet. Other sources give a far lower average bullet drag force.

The 7.62 NATO releases about 11 BTU of chemical energy. Hatcher's notebook has some old military data suggesting 22% of the gas energy goes to barrel heating and 7% to bullet friction. Now, 7% of 11 BTU is .77 BTU, about in line with the 1 BTU figured above.

My notes don't record if Hatcher's 22% for barrel heating includes or excludes the 7% for bullet friction. The table I recorded suggests it is excluded, so his numbers imply convective and radiative heat transfer from the gases to the barrel are triple the heat energy of bullet friction.

Does it really matter? Personally I think it is more from burning powder than friction/velocity. This is based on nothing but opinion. I do know that a .257 Weatherby will get hot quicker than a .257 Roberts, and I can't see where the friction would be any different. The amount of powder burned is considerably different.

Etoh,

I don't think your post was present when I started mine, but it was there after I clicked SUBMIT. You did answer the question, I just didn't see it in time. Thanks for the insights.

Hi folks... great thread!

Just wondering if anyone caught this. This is from an article on Berger bullets written by Berger. It's in reference to how very occasionally, one of their thin-jacketed VLD's would literally blow up midair...

"As it turns out the bullets were heating up to the point where the cores would actually melt. Once a bullet leaves the barrel with a melted core it is certain that the molten lead will burst through the jacket under such high RPM. Obviously this was a problem that we needed to resolve so we decided to test a thicker jacket. Making the jacket thicker did not make it strong enough to contain molten lead but rather it moved the lead away from the source of the heat. The source of the heat that can melt a core is the friction between the bearing surface and the rifling as the bullet travels through the barrel."

http://blog.sinclairintl.com/2011/03/16/history-of-the-match-grade-berger-hunting-vld/

this aspect of the topic is about 30 yrs. old, and was frequently asked to speer enj. about their varmint bullets in swifts which seem to vaporize out the barrel. There answer was that the engraving from the rifling was cutting through and the bullet lost its jacket. While the number of revs may be a first daunting it still has to travel a foot or so to complete one revolution, to in say 400 yds its only completing 1200 rev.-- not that much. Softer lead will obtruate more than harder lead giving the appearance of being molten, as any bullet caster knows. If this is the complete story it will be easy resolved by contacting Brian Litz at Berger for the rest of the story.

Etoh,

The promlem is not the number of revs, but the rate. If the twist rate is 1:12", and velocity is 4000 fps, then the rotation is theoretically 240,000 rpm. That sounds pretty fast for a thin copper jacket containing [molten] lead. I've seen some things blow-up at much lower rotation rates than that.

Sure but its not spinning long enough for that force to act on it. Maybe 1/2 second. 240000/60= 4000/2=2000revs per complete time of flight cycle.

all i will say is even with alot of shooting ive never had a pellet or bb guns barrel get to hot to touch.......

I've never had a bullet blow-up in mid-air, but in the instances of such that I have read about and heard about, it happened pretty close to the barrel's muzzle, not 2000 feet downrange.

"I've never had a bullet blow-up in mid-air,..."

I have. It was those Speer Plinkers of about 100 grains in .30 cal. I loaded some to about 3000 FPS in a .30-06, and they blew up about 10-15 feet from the muzzle.

I don't know if these bullets are still made or not. They were light bullets with a lead core and a half jacket.

I have also seen .220 Swift bullets leave a vapor trail, or else maybe it was a tail of melted lead that I saw.

I've had a number of bullets come apart after leaving the muzzle in various degrees.

Sometimes they come totally apart soon after exiting. If this happens a dark cloud will be seen briefly, more often by somebody else than the shooter. Though I have seen it through the scope. It's particularly interesting when shooting at a prairie dog on a typical dry summer day, and no dust cloud shows up anywhere near the prairie dog--which of course survives.

I've also seen a lead swirly-pattern around bullet holes on a paper target, and also seen bullets zip way off to the side of where they were aimed--as in as foot or two instead of a couple of inches.

It's possible to put some real numbers to the question.

From my previous post, the work that is converted to heat is 300 ft-lbs, more or less. That is the energy that is available as heat, and it is much less than the energy originally contained in the powder. So most barrel heat still comes from the original heat of the powder, not the derived heat of friction. However:

300 ft-lbs is .4 KJoules.

A 180 grain bullet (arbitrary choice) has .0116 Kgrams of mass.

It requires 23 KJoules of heat per Kgram to melt lead.

.4 KJoules/.0116 Kgrams = 36 KJoules/Kgram of available heat from friction. This is greater than the 23 Kjoules/Kgram required to melt lead. But for this to happen, most of the heat from friction would have to end up in the bullet. I don't think that is a reasonable assumption because a lot of the friction heat ends up in the barrel. So I don't think that the heat of friction would come close to melting a 30 cal 180 grain bullet. Other bullets require a fresh calculation. I would expect that if bullets are to melt from friction, they would have to be smaller, lighter bullets.

Sierra contains or used to contain a warning with 22 cal blitz not to shoot over 3500 fps. because of separation.

Denton:

What about the conductivity of the mostly copper jacket? Copper conducts heat much better than steel, so it seems likely that most heat from friction, if any, would be conducted through the jacket and into the lead core.

I have fired high velocity bullets into dirt banks and dug them out soon after, and many were too hot to hold in my hand. The heat came from somewhere, either from friction or the powder gases.

I don't think it is too unreasonable to think that some of the heat comes from frition.

As an example, take the SR 71 airplane. I have read that some parts of this plane get red hot at speeds approaching 2000 MPH, and this is because of friction from the air, and thin air at that, because of the altitude.

Many bullets are traveling faster than 2000 MPH. Is it unreasonable to think that friction from the bullet's flight through the atmosphere would not produce heat?

This is no argument. I find this to be an interesting subject, and I would like to learn more about it.

1--7: To answer only part of your question about hot bullets retrieved from dirt.

Those bullets ALSO came under intense friction upon contacting the dirt or whatever the medium. However warm they may have been from leaving the barrel, they were heated much more upon contact with the dirt.

If you ever shot a bullet into SAND, it's like being exposed to a sand blaster or belt sander. IF there's anything left it's HOT too.

IMO the HOT brass cases ejected from semi or auto rifles PROVES the majority of heat is produced by the BURNING POWDER. Those cases have NEARLY no friction force upon them for any length of time or distance traveled.

MD,Mr. Howell, & Denton gave the essence to the question on P 3-4 of this thread. I concur.

JWALL
__________________

VEGETARIAN.........Indian Word For Poor Hunter

usually the pressure or shock wave ahead of the bullet protects the bullet from rain, sleet, and hail, air. Some effects from spin drift, earth spinning, the need to convert to knots when shooting over water etc. The biggest effect comes from gravity. The time of contact of bullet with barrel wouldn't allow for that much heat content to transfer.

The vapor tail is called a trace by the way, and there are some really good downloads on sniperhide if you wish more on that.

Interesting questions.

I've noticed three things that cause these rifle barrels to get hot and hotter:
1. Chemical reaction in there, one product of which is heat.
2. Some friction (bullet to bore) which will cause a bit of heat.
3. Sunshine on the barrel on a clear/warm day.

The speed (quicker?) at which the barrel gets hotter seems affected by several factors: quantity of heat (chemical + physical)) generated; frequency of applied heat (time between chemical reactions - shots taken); the propensity of that barrel to have its accumulated heat dissipate; ambient temperature and wind (heat exchange factors) and maybe other minor factors.

I don't think you're thinking about this quite right. ;-)

From the instant the bullet leaves the barrel (using your figures above), the widest portions of the jacket are enduring over 180,000 G of centripetal force (if my calculation is correct, but I'm pretty sure it is...it's just r*w*w where w is the angular velocity in radians / sec - I converted everything to MKS units). If you were to endure 180,000 G in a floorward direction for 1/10 of a second, you'd be a thin red film on the floor of whatever you happened to be standing on. Hitting concrete at terminal velocity would be much less traumatic.

That is a LOT of force working to rip the jacket off the core. I've always been amazed bullets resist deformation as well as they do.

yup so would be accelerated to the speed of light be dramatic, but back to guns, torque on the bullet and coupled with the engraving process isn't gettin anywhere enough press.

Wore a neat looking little .22 Long Rifle case brand for most of a Summer once. Between the right earpiece of my shooting glasses and temple.

From a 10/22. a hot day, and the rifle had been fired quite a bit. Got it flicked out of there in a second or so.

It felt very hot to me at the time.

I read this a long time ago, so in may not be 100 percent accurate, but talking about the heat from a cartridge case ejected from a semi-auto.

What I read was that the action opened while there was still some gas inside the barrel, and that escaping gas was what made the case so much hotter that a like case fired in a bolt action or other manually operated repeater.

This is easy enough to prove. Operating a bolt action as fast as you can, the fired case would only be warm. There would not be enough time for it to cool down that much, if the brass was heated by the powder gases. I don't think the heat from the brass would conduct into the rifle's barrel that fast, enough to make that much difference in the temperature of a cartridge fired in a semi-auto as opposed to operating a manually operated action as fast as you can.

I have never ejected a cartridge from a bolt action that was too hot to hold in my hand, although I have picked up brass off the ground that was fired in semi-autos that was still too hot to hold in my hand. The brass was ejected and lay on the ground considerably longer than it was left in the chamber of a manually operated rifle, yet it was still too hot to hold, indicating that it was very hot at the time of ejection.

Watched a left-handed pistol-shooter invent some wild and leapy new dance steps when a spent case from his .45 auto ricocheted off the divider at his right and into his open shirt front, right into his exposed chest hair (no skivvy shirt).

The same sort of thing plumb discombobulated a well known pistol champ when he saw an ejected case from his .45 fly into the cleavage of a busty female next to him on the firing line.

She was wearing a tank top and no bra, so he was already somewhat distracted.

Ken,

Being left-handed I've had several ACP cases go down my collar over the years. They were minor compared to a 7.62x51 from an M1A.

Its the cycle time. If you can cycle a bolt as fast as an auto for example, the caswes from the bolt would be as warm. Lets see that would be around 800 for an ar, around 600 for an Uzi etc. Its not possible to get to the bolt fast enough. This feature is used in select fire weapons as an advantage. The ejected brass acts as a "radiator" to pull heat off the weapon before it can be absorbed. Gas opertated weapons are designed with escape ports to remove this gas after the bolt assemblies have moved a specific distance so as not to have gas left in the barrel.