The specific head of brass is 2X that of steel. That means that your brass case require 2X more heat energy to raise a unit mass 1 degree (e.g., Celsius). Brass and steel have have similar density, so a steel and brass case for the same cartridge would have roughly the same mass.
So when a brass case is ejected from your action, carrying with it the heat energy from the fired round, it should be actually cooler than a steel case. But in actual practice, I believe that both are equally hot, meaning the brass case is carrying more heat away than the steel case.
Brass is better here in that it ejects more heat energy away from the gun. What about plastic cases? They carry away almost no heat energy when ejected, letting the gun get very hot indeed. VERY BAD FOR THE GUN!
More specifically, the barrel, as was mentioned later. You're using what I call 'liberal logic' (Not calling you a liberal, this is just what I call the 'If x is good, 2 times x is twice as good' line of thought. It is far too prevalent these days.) Barrels are replaceable, and on the types of firearms this is most applicable to, (belt-fed MG's) is accounted for by having a quickly replaceable barrel.
That would be “another reason why…”.
Things like this
View attachment 1032589
and poor neck tension with regular bullets are above heat transfer on my list.
Because annular neck separation never happens with brass cases....
Ask me how I know.
Just a thought; I have seen videos of guns run full automatic until the barrels glow (and some melt and sag). In none of these destruction videos does the action or chamber get hot enough to make the steel glow, so most of the heat is directed down the barrel. If some member has an infrared thermometer perhaps they could measure temps of brass, vs steel cases or aluminum cases or even the Shell Shock two piece nickel alloy cases? That would be interesting. I saw the above video quite a while ago, but I have never seen one of the "plastic" cases or know anyone that has, has the Armed Services dropped the experiment?...
Indeed, I have done this with M16A1's, and while the receivers warmed up some, I could still touch them. I did not go to the point of the barrels melting or sagging because I was just shooting up leftover ammo from a qualification range instead of doing the extra ton of paperwork it took to turn it in. But I did notice that the heat buildup, evidenced by the glow, started at the gas block and slowly worked it's way back down the barrel. My roommate lit his cigarette off one. When we had to stop firing to refill magazines, it would start to work it's way back up the barrel, then down it again when we started again. We couldn't maintain a rate of fire enough to get the whole barrel to glow, and the receivers remained touchable the whole time.
With the M249, the very early models like jmorris shows above, we could have easily got the whole barrel glowing, but since they were new and not my unit's, we didn't. I Borrowed them from another Armorer I went to AIT with for familiarization. About 6 guys from my unit wanted to 'get to know' the M249, and one was the S-4, a Green Beret CPT, so we ordered M855 ammo and I borrowed the M249's. A fun and informative range day.
Keep in mind:
Why is water such a great coolant in car engines? Because is has a VERY high specific heat. Substances with high specific heat are good for cooling things. And brass has a high specific heat compared to other metals.
Why is water
not a good coolant for MG's? Because it turns into steam at 212F, and the cycle of water steam, condensation, to water again, is too too slow for belt feds. The Russians and Finns had a good idea with the water jacket with a large hole on top to dump snow in, as most of the year, it was in unending supply.
Water by itself, BTW, is
not a good choice for an engine coolant. Adding ethylene glycol to it increases it's useable temperature range. This is not transferrable to firearms, they get much hotter than car engines, but for shorter time periods.
As you pointed out, Specific Heat by itself doesn’t tell the whole story:
Specific Heat Capacity of Metals Table Chart
Metal J/(kg-K)
Aluminum 921.096
Brass (Yellow) 401.9328
Carbon Steel 502.416
So aluminum has a higher spec. heat than either brass or steel but if you were using aluminum, the mass per case would be a fraction of that for brass or steel. Same for a polymer.
But the heat ejected is much less than I would have expected. That’s the killer for my assumption. You can’t fight the numbers. I surrender! Long live plastic. (That’s like fingernails down the chalkboard!)
All of these methods to cool off full auto firearms have been tried, many of them soon after full autos were developed.
Aluminum (as a sleeve/heat sink around the barrel) as early as the Lewis Gun.
So reloaders go by way of the dodo bird?
Unless it's specifically loaded for reloaders, like the .38's shown in a previous post, those who develop such rounds are not concerned with reloaders.
What about Sig Sauer’s new Hybrid Ammunition?
A brass-steel hybrid.
View attachment 1032721
They’re completing for the same Army contract as the plastic stuff is.
An example of an earlier method of brass cases with steel heads was shown earlier in the thread.
Yeah, but they are probably trying to recoup some up front R&D and investment costs. All other components (Bullet/primer/powder) being equal, if the poly case costs half or less than a brass case, they should be able to get prices down in a short time. A large military contract would certainly speed things up on that end.
It's not like regular brass cased .308 is a lot cheaper right now-if you can find it.
Why? Do bullpups not like plastic ammunition?
Well, if the plastic stuck in the chamber and the brass didn't, you might be breathing in some
hot air, and lose your eyebrows and beard for a while. I've never been fond of bullpups simply because the receiver is alongside the face, should it have a catastrophic failure. Yes, I know it's a small risk, but still...
I once read that the magazine well was kind of sloppy and shooting a Minimi from AR magazines was not real reliable. Did yours work well?
When the 7th got theirs, ('87) some of the new SAW gunners went out and bought the MWG 90 round 'snail drum' available at the time only to find that they were even less reliable than using 30 or 20 rounders. I tried the 30 rounders in the ones I borrowed, we had a couple failure to feed, but it'd work in a pinch.
