Home Forums Hunting & Shooting Ask The Gunwriters Opinions about the effect of Carbon deposits on throat erosion

I'm trying to get some info.so I can refine my theory.
Carbon is a very good conducter of heat,especially through its ends.As carbon fills up the micropores in the throat area it creates ends at the bottom of the micropores.It shunts the heat from firing to these ends and it is absorbed by the barrel steel,and passed to the outside of the barrel and disipates to the atmosphere.I think these heat cycles and carbon transfer contribute to but aren't the only factors involved.The carbon however will conduct and transfer heat faster than the barrel steel can,so we get heat build up.

Anyone think there is any merit to this?Let's hear your theory.

Where am I going with this?I'm asked how UBC slows throat erosion.It insulates some what and fills the micropores so the carbon can't go into the steel.This is only part of how it works,but it's the hardest part to get a handle on.TIA to everyone.

Doug,

I dunno about carbon transmitting heat, but Dan Lilja has some interesting opinions on carbon fouling actually helping a rifle shoot better. I hate to put words in his mouth (and you might check out his website), but he apparently feels that carbon fouling fills up the little holes in the steel and makes a barrel smoother--so efforts to get rid of it when cleaning are just not the best idea.

Sound like a certain product I am familiar with....

Remember the admonishment to 264 owners: " Keep your barrel clean if you want it to last."

I cannot comment about the chemistry or the metallurgy of it all, much less the thermodynamics. But I do know two things: One; if we shoot, we're going to deposit carbon, and we're also going to erode throats. Two; barrels are replaceable, likely for a reason.

See ya at the range!

Doug,

From my physics and nuclear plant background I am thinking that the carbon coating in the barrel will be more effective shielding the 3,000+ degree blowtorch at firing from the metal (a microsecond time scale event) than modifying heat transfer (millisecond and longer scale).

By teh way the brass cartridge has a major role in carrying heat away from the chamber on ejection, something only realized recently in machine guns and caseless ammunition research.

Understanding materials behavior on this scale can be a bugger (technical term).

jim

Jim, some of us understood the cartridge case heat transfer thing a long time ago, learning it with total grasp the first time a piece of M-16 brass went down our shirt!

Or from a mini-gun firing from a bird that happens to be right over you. And those cases come down in buckets!!

Rocky,

I did watch a rather well-endowed young woman with a low-cut blouse catch a 9X19 casing! It was a funny incident, after she got over the burn.

jim

I think you might want to set out your basic premises first. I have a few questions too. Hope you don't mind



What are these "micropores"? Are you saying that the forged steel is porous? Do you have any micrographs? What is the typical size of this "microporosity"? Is the size and extent of this "microporosity" a function of production method?

Also, do you say that there's a buildup of carbon in this zone which survives firing rather than being removed by the high pressure and flame of combustion and being replaced by the residue from the next round? I mean, we are talking about soot, fundamentally.



I agree that taking the heat away as rapidly as possible from the momentary superheat in the throat on firing is a factor in the rate of erosion. Steel, being a pretty good thermal conductor, does this reasonably well. I don't entirely see what carbon fouling has to do with it though. It strikes me that any soot left behind on firing is likely to be no more than a bystander as far as the transport of heat from the bore surface to the substrate is concerned.



Sorry, I don't understand that at all. Where do you say the heat builds up as a result of this mechanism?

daniel,
I don,t have any graphs,I'm just fishing to see if a theory will hold water.Yes steel has micropores caused by off gassing as it cools.Carbon can be seen in the throat area as a glaze,if you go to Dan Liljas web site he explains it better than I can.Carbon is a very good thermal conductor,this is why NASCAR uses it for head gaskets.It's layered in the center of the gasket with continues fibers running lenght wise in the gasket.Carbon dtransfers heat faster than steel can dissipate it to the atmosphere.The heat build up would be seen in varmit or high volume firing.As I say I'm just trying to see if the theory has any merit,probably not.

John,I'll go back to the fact that UBC fills all the micropores and acts like a good stand of grass on a hillside.If we get a bare spot in the grass this is where the erosion will start.

Jim,your right,this is why NASA makes the nose cone on the shuttle from Carbon Carbon.If you can setup a demo of the hot brass bown the front of the shirt again,I'd be there to watch,and render firstaid.(grin)

Thank you for your answer.


Micropores caused by "off gassing"? You'll see a bit of gas porosity in a cast ingot or billet, but by the time you've forged that down to bar stock all that porosity has well and truly been eliminated. If that wasn't enough after you deep-hole drill it you either cold form it by rotary machine or by buttoning, and you end up with a really nice dense, fine-grained microstructure, without porosity.

Have you ever seen microporosity in a finished barrel steel? I've sectioned and examined a fair bit of this sort of stuff, at high magnification too, and I haven't seen it. Indeed one of the features of forged steel is that the process eliminates porosity. A well burned throat may well exhibit some degree of checking, but of course this is quite a different phenomenon.



Not all carbon is the same. It exists in different forms, with different properties: diamond, graphite and amorphous carbon for example. Carbon fibre does have good thermal conductivity along its length (though quite poor across) but of course that isn't what is deposited in the leade. Amorphous carbon has quite low thermal conductivity - less than 1/1000 of that of carbon fibre measured along the strand.



If the powder fouling had any effect at all it would likely be by absorbing a fairly tiny amount of heat energy as the area in which it sits is momentarily superheated. Given the tiny volume involved the effect would be very small.



Erosion is essentially a product of the steel surface in the throat momentarily being superheated above its melting temperature, and simultaneously hit with a very high pressure gas stream (with a certain amount of entrained particulate combustion product). The superheat is quickly soaked away by the underlying substrate (as long as you aren't firing rapidly and thereby heating the substrate and compromising its ability to draw heat from the throat surface). You can mitigate the effect by using a coating or liner with a greater resistance to heat and/or the scouring effect, such as hard chrome or better still Stellite (Co alloy).

What daniel says.

Having a Material Science background I'll add a little... Carbon deposits in throats are unoriented, probably tending toward amorphous, so not efficient at conducting heat. The thermal mass of the carbon build up is also neglible compared to that of the barrel steel, so the carbon isn't going to conduct heat. In addition to erosion due to superheating and particulate scouring, build up could either increase or decrease friction and pressure of the bullet passing through the throat. Passivate the surface of the steel with a coating (purposeful build up that's beneficial) that prevents erosion and friction and throat life will go up.