So what IS carbon fouling, actually?

[1168]

From the cherry balm lube thread:

AR-15 Lubrication - An Interview With CherryBalmz

For those that feel like geeking out on the science and engineering that has gone into this stuff. It's interesting at the very least.

That was an interesting read. Most interesting was the part where the interviewee claimed that the stuff we tend to call carbon is really mostly copper and lead with some other metallic stuff. And that most carbon from propellant actually goes out the muzzle as CO2.

So what is the crap deposited inside my gun actually composed of, and even more importantly, what is the cloud of crap I’m huffing while shooting suppressed composed of?

1168

[Leonidas24]

Double base powder not withstanding, normal black powder is a simple mixture of saltpeter (KNO3), charcoal (C with some contaminants), and Sulfur (S.) The stoichiometric equation looks like this (simplified):

(10)KNO3+8C+3S --> (2)K2CO3+(3)K2SO4+6CO2+5N2

This is incredibly simplified because in black powder combustion the propellant isn't completely consumed by the reaction. In single/double base combustion the reaction is more complicated because of the addition of inhibitors which slow the burn rate. Generally speaking in smokeless powder combustion the propellant is completely consumed and exits the firearm as a gas. The "carbon" or black sooty substance that's left on the BCG are typically salts of lead, copper, antimony, and tin. Look at ARs or any rifles really that are often shot with a suppressor. The fouling with often oxidize into various shades of blue and green, both of which are indicators of copper oxides. The gas you're breathing when firing an AR is a mixture of CO2, N2, and various atomized metals and salts of metals.

[hotrodder636]

I am sure if a spectrography was performed you would find carbon, lead (antimony and tin—used to adjust the hardness of the lead), copper, brass all mixed into a the buildup, as Leonidas points out above.

[glockycharms]

Saltpeter? oh no now i got flashbacks to bootcamp!!!

[ViniVidivici]

So I should shoot with my pro-mask on more often. Wilco.

[Chubbs103]

Shooting Times did a test on lead free primers. They resulted in considerably less fouling. I was surprised the primer made that much of a difference.

[1168]

Shooting Times did a test on lead free primers. They resulted in considerably less fouling. I was surprised the primer made that much of a difference.

Thanks; maybe its time for me to take more interest in lead-free primers.

[Clint]

Here is a slightly condensed snippet from the article, that answers the question of "what is fouling made of" and "why are ARs so lube sensitive".

Dallas Frohrib, CherryBalmz – So, in regards to AR-15 lubrication, you hear a lot of people say ARs like to run wet, right?
They’re more lube sensitive than most because the DI system is pumping a lot of gas into that action area where the lube is.

The thing is, when we started running the numbers, DI guns were simply burning off oils a lot faster than they should have been.
CLP, motor oil, whatever…We knew we were missing something, as the heat and volume of the gas just couldn’t account for the amount of burn-off that was occurring.

When we dug into it, the fouling that all of us have been calling “carbon” for so long?
Well, it turns out there’s almost zero carbon in combustion fouling at all.
It’s about 98 percent lead and copper particulate, coming out in rough sphericule shapes between .5 micron and 10 micron, with the final two percent being things like tin, antimony, or steel, depending on the composition of the cartridge.

In rifles you’re looking at a 70/30 copper-to-lead ratio, and in pistols it’s flipped, at 30 percent copper, 70 percent lead.

But yeah, almost all the carbon in the powder is converted to gasses, like CO2.

...

So it’s this super-heated, dense metal particulate that was causing so much of the AR-15 lubrication burn-off in DI ARs, and suppressed guns.
The temperatures inside a cartridge at ignition are right around 5,000 degrees Fahrenheit for a microsecond, and go down to about 3,000 degrees Fahrenheit two to six inches from the chamber.

...

These temperatures atomize these different metals, and under these extreme pressures in the bore they start getting recombined into this spherical particulate, but it’s the density of these metals that allows them to retain such extreme heat for far longer than the gasses they’re carried in.
And that’s the key friction challenge you find in DI ARs, and suppressed guns.

The friction of the particulate itself, and how rapidly it polymerizes or burns off most lubes.
It’s also why the cam pin and cam channel are the most under-appreciated friction surfaces in an AR.

[AndyLate]

I don't remember which one it was now but there is a bulk / low cost 223 ammo that leaves a very bright green fouling. It surprised me, and I have been shooting for a long long time.

Andy

[ViniVidivici]

I've read that lead-free primers don't last as long as others.

Do not want.