Myth of brass carrying away heat from a chamber

[awgrizzly]

I read an article about some type of bullet that doesn't have a brass case. It was long ago, I am old, so I can't remember the details, but I think it was probably one of those rocket type rounds with the powder in a hollow behind the lead. Anyhow it didn't work, one of the problems they had was overheating because it lacked brass cartridges carrying away some of the heat. It wasn't much heat, but in rapid fire it adds up fast. Like RC said, it doesn't cool the chamber, but it prevents the chamber from getting hotter.

You have a certain total number of BTUs making your gun hot, part of it contained in the brass. Remove the brass and poof, out goes some BTUs that would have otherwise sat there smoking away in your chamber.

 

[jmstevens2]

"The Laws of Physics" are only the "laws" as we see them now. The Earth is not flat for example. We learned that we were wrong about that. The "Laws of Physics" are only "laws" at the moment.
One day we may have to change them.

 

[Certaindeaf]

Wormholes is cooler than brass.

 

[BCRider]

"The Laws of Physics" are only the "laws" as we see them now. The Earth is not flat for example. We learned that we were wrong about that. The "Laws of Physics" are only "laws" at the moment.
One day we may have to change them.

Unlike the laws we make up the laws of physics and thermodynamics are a lot more constant and set by the world around us rather than politicians. So good luck on seeing them change any time soon.

Even if we find some loophole that changes time and space and gives us faster than light travel it won't change the laws of thermodynamics or the thermal behaviour of the metal used in our firearms. Mother Nature saw to that. And you gotta know that "Mom" is always right...

 

[bigfatdave]

I read an article about some type of bullet that doesn't have a brass case. It was long ago, I am old, so I can't remember the details, but I think it was probably one of those rocket type rounds with the powder in a hollow behind the lead.

gyrojet?
volcanic pistol/rifle?
fancy german caseless prototypes?
That "not really an airgun" thing that used the heat of compressing air to set off a charge?

 

[Sam1911]

If what you say is true, then having a line of spoons dip into the hot water constantly should keep it from boiling.

Obviously, they would. That's pretty much how all heat exchanging temperature control systems work. Keeping water from boiling would all be a matter of how many spoons, at what initial temperature, passing into and out of the heated water, at what rate. Too much hot water, too much heat going in, not enough spoons...water boils. Balance the system right, though, and the spoons will take heat out of the system fast enough to keep the water temp below 212F/100C.

For that matter, does a bolt action rifle get hotter from not ejecting a cartridge from it?

Incrementally, yes. Heat enters the system from the combustion of the gasses. Some of that heat enters the brass case. Some enters the barreled action directly from gas touching the bore, some comes from the friction of the bullet passing down the rifling. Fire the action and leave it set -- the heat will transfer between the cartridge and chamber until they are at equal temps (and then the whole system begins to cool). Eject the cartridge quickly and some amount of heat does not equalize between the cartridge and chamber walls. This may be an almost inconsequential quantity, though inconsequential quantities add up at high rates of fire.

And does it suddenly get cooler or not get any hotter then X by cycling a cartridge through it?

Now, that equalization could happen in two directions. If the barrel was very hot and you simply cycled cool cases through it over and over (no firing) then the cases would absorb a little heat from the action and carry it away with them -- dropping the temperature of the chamber.

But you're actually firing a round each time which adds heat. The cartridge case gets hot, immediately, but if it gets ejected before all that added heat transfers to the chamber, the barrel isn't getting as much heat from each round as it would if you fired the round and let the case sit until the heat equalized. Thus the barrel is cooler than it would be -- though the total heat gain from many charges of heat from firing rounds rapidly will of course be greater than the total amount of heat not transferred by cases that get ejected quickly.

You're heating and then tossing away a very small "heat sink" with every shot. It isn't enough to keep the system from overheating eventually, but it does seem to help. Obviously the caseless ammo system tests indicate that the effect does exist, though other factors are probably in play as well.

 

[PercyShelley]

Caseless systems get hit coming and going.

In a cold barrel they lack the case to absorb some of the heat from firing, so the chamber heats up faster.

In an already hot barrel they lack the extra thermal mass of the case, which soaks up some of the energy before it can start heating the propellant.

 

[saltydog452]

Just a guess, but if there wasn't the possibility of rounds 'cooking off', maybe automatics wouldn't need to fire from an open bolt.

And I wouldn't to need to keep a pot of beans or chili on the back burner for 4 hours to make it 'just right'.

Heat is cumlative. I don't know about thermo?, but Texas is way hotter in July/August than in May/June. Its just had time to 'cook' longer. in July/August.

Thanks for the intermission,

salty

 

[Cosmoline]

Removing heat that would otherwise be in the steel is only a secondary benefit to casing. The major benefit is removing the crudola that, absent the case, builds up very quickly and makes chambering more and more difficult. Caseless ammo can get around this to some extent by being undersized in the chamber or by having soft wrapping, but eventually the crud wins. The crud ALWAYS wins. Until someone comes up with a new propellant that leaves no residue from combustion, we're stuck with cases.

 

[Mxracer239y]

No one is claiming that the brass actually removes heat from the chamber; It simply prevents as much of the heat from being transferred to the chamber during ignition.

Heat transfer is not a simple subject, and there's a lot more to it than a layman understanding of basic thermodynamics.

While I agree with much of what you posted (especially the last sentence), I would suggest the brass lowers the temperature of the chamber before the round goes off. More precisely, the chamber transfers heat into the brass, the round is fired, and the brass transfers heat into the chamber. The 'net effect' depends on a number of variables: temperature of the chamber, thickness of the brass, time brass is left in the chamber, time between ignition and extraction, level of fouling in the chamber, et cetera. Assuming the proper conditions, it is plausible that the casing could have the net effect of lowering chamber temperature.

Interesting fact: The thermal conductivity of yellow brass at 68 degrees fahrenheit is more than 3 times that of steel (with a <1.5% carbon content). Makes one wonder about the effect of steel-cased ammunition in a select-fire weapon. The polymer coating on wolf ammunition would have an interesting contribution as well. (cite: engineeringtoolbox.com)

 

[MachIVshooter]

Just a guess, but if there wasn't the possibility of rounds 'cooking off', maybe automatics wouldn't need to fire from an open bolt.

Some machine guns (most notably the Maxim, Vickers, M2 and M1919) and virtually all assault rifles fire from a closed bolt.

While I agree with much of what you posted (especially the last sentence), I would suggest the brass lowers the temperature of the chamber before the round goes off.

In some minute quantity, yes. It would take precision equipment to measure the change, though-especially with a machine gun.

 

[briansmithwins]

I'm kinda surprised that there is any argument about this at all.

Does anyone here deny that ejected brass is hot after firing?

Given that, a mass of brass weighing X grams wih a temperature of Y must have removed that much heat from the mechanism of the gun. If the brass stays in the gun the heat content of the brass will heat up the mechanism until the temps equalize.

BSW

 

[mshootnit]

I got the second highest grade in my college physics class and I can assure you at no point during the semester did I ever type anything approaching some of the word counts I see on these threads. Fully describe the Heisenburg uncertainty principle and how it applies to the current discussion.
And then when you are done explain how one can be mathematically certain.

 

[gpb]

Heisenburg uncertainty principle and how it applies to the current discussion.

So, if we put a round in a chamber and we can't observe it, we won't know if it's alive or dead?

 

[fatcat4620]

OMG I need some whiskey!

 

[SleazyRider]

I got the second highest grade in my college physics class and I can assure you at no point during the semester did I ever type anything approaching some of the word counts I see on these threads. Fully describe the Heisenburg uncertainty principle and how it applies to the current discussion.
And then when you are done explain how one can be mathematically certain.

I don't have the advantage of an education, so perhaps you could further explain this Heisenburg principle. Thank you!

 

[briansmithwins]

I don't have the advantage of an education, so perhaps you could further explain this Heisenburg principle. Thank you!

I would, bu I'm uncertain as to how to go about it.

BSW

 

[WNTFW]

Sleazy it is a trick question. The Heisenburg blowed up and burned. Heat was released. There was no chamber for the heat to transfer to. They did get it on film. So trick question.

Heisenburg uncertainty principle is sometimes dirigibles blow up and sometimes they don't.

The Heisenburg uncertainty principle doesn't apply as a blimp is not brass cased. Neither is a dirigible.

Obviously, Not really! just clowning around and seeing how many people will let this set them on a tangent argument, rant or whatever. Meanwhile I wlll be googling the H.U.P.

 

[hogshead]

I think I will just accept your version of it WNTFW. Because I'm kinda like Homer Simpson every time I learn something new I have to forget something I already knew.

 

[MachIVshooter]

Fully describe the Heisenburg uncertainty principle and how it applies to the current discussion.

It doesn't. We're not concerned with the position or momentum of the casing.

Heat transfer between a cartridge case and chamber wall is not quantum physics. It's thermodynamics.

If all the specific variables were known, one could calculate the amount of heat the casing absorbs prior to firing and the amount it deposits after firing, thus knowing how much cooling effect (or lack of heat transfer, as it were) is present. Of course, the number of variables that need to be accounted for are substantial, and as soon as you change any one of them, the entire calculation changes.

The really important part is that it doesn't matter one bit, other than to satisfy curiosity. We all (well, almost all) understand that brass (or aluminum, steel) cased cartridges do not have the problems that caseless ammunition does, and why.

 

[WNTFW]

Hogshead
It's pretty simple to me. I know how long before I can pick up the brass from an AR, Garand, bolt gun or pistol. There is just some stuff I prefer not to concern myself with. I have been burned before by a .22lr that took a series of bad bounces & then rolled between my glasses & face. In layman's term I didn't like it. I have no scientific explanation other than the case was hot and the skin on may face is more sensitive than my fingers.

 

[WNTFW]

Mach IV,
Your 3rd paragraph (If all the specific variables were known, one could calculate the amount) reminds me of a discussion in a driving school. A student posed the question: If we could measure all the variables that made up a corner could a computer figure the fastest time a car could make it through the corner. The instructor said: yes, I guess somebody could do that, but it would be be way easier just to drive through it a few times.

I realize the discussion is academic and there is something to be learned.

 

[Art Eatman]

The burning of the powder charge produces a certain quantity of heat. Heat which remains with ejected brass is heat which does not get transferred to the steel of the barrel.

The hot brass has not cooled the steel. It merely reduces the rate at which heat builds up in the steel.

 

[Lunie]

Well, if we're gonna toss the 2nd Law around...

Let's define an Initial State to be the chamber just after the firing of a cartridge. Both the barrel and the empty cartridge case have previously, and quite rapidly, absorbed a given amount of energy in the form of heat.

Final State: The emptied chamber.

Ejecting the fired case removes both the mass, as well as the energy that was stored within it.

The net result to the system is a loss of mass (the cartridge case), and a loss of energy (the heat associated with it). Had the case remained inside our system, the energy would have been primarily dissipated through the chamber walls. So by ejecting the case, there is less heat that must be transferred to the environment. (Well, there is less energy remaining inside of the system we defined as our chamber, anyway.)

Now how about someone calculate the entropy generated by the irreversibilities in the process, and then we'll call it a day.

This is how I would set up the situation, with some assumptions already included.
System: Open (Chamber)
Mass balance: [ dm/dt = d(mass;in - mass;out)/dt ] ===> [ dm/dt = d(-mass;out)/dt ]
1st law: [ dQ/dt - dW/dt - Σmass;out*(h;out) = dE/dt:system = dU/dt ]
2nd Law: [ Σ(dQ/dt)/T;0 - dS/dt;out + dS/dt;gen = dS/dt;system ]



What's the rub? Looking at what I have, I can't see how ejecting the case in any way increases the amount of energy in the chamber. And logically, that makes sense. So REMOVING the case does not make the chamber HOTTER.

What else? If anything, ejecting the case works to reduce the amount of energy in the chamber more rapidly than if we had just left the case inside, by reducing the total amount of energy in the system, and likely increasing the rate of heat transfer to the environment, even if only slightly.


Result? The chamber stays cooler if the case is removed. IMO.


Disclaimer: I'm not an expert, a lawyer, a robot, a... You get the idea.

 

[JohnKSa]

stored heat, not "overall temp."

Sloppy terminology. I should have said "equilibrium temperature". The stored heat is the same, it's just spread over more mass.

...I would suggest the brass lowers the temperature of the chamber before the round goes off. More precisely, the chamber transfers heat into the brass...

Interesting.

So three effects so far, some admittedly far more significant than others.

1. The brass is ejected before equilibrium temperature is reached, carrying away heat that would otherwise be "shared" with the chamber.

2. The brass adds to the mass of the system, so to the extent that heat is "shared" between the brass and the chamber, the temperature reached is lower because the heat is distributed over a larger mass.

3. The brass is cool when it is chambered and therefore absorbs some heat from the chamber before firing.