The carbon is coming from the cellulose part of nitrocellulose. Cellulose is a carbohydrate polymer that makes up plant fibers, wood, cotton, rayon, etc. Cellulose is made by plants "fixing" carbon dioxide from the atmosphere in a process called photosynthesis. An example of the carbon content of cellulose is that under pressure for 270 million years and cellulose becomes coal, more pressure graphite and even more pressure diamonds.
When I use Reloader 25 in my 6.5 WSM I often refer to it as "burning soft coal." The comment has some truth.
Cellulose treated with Nitric Acid produces Nitrocellulose which is single base smokeless powder. The nitrocellulose is a polymer which was used at one time to make photographic film. Running a projector in a movie theatre was at one time a dangerous job because of the nitrocellulose. Under desperate circumstances photographic film has been cut into pieces and put in handloads in place of powder. I tried it as a youth. It works, but you still have to have a primer.
Herter's used to sell paints, for painting fishing lures and duck decoys, that used nitrocellulose dissolved in ketone as a polymer base. "Celluloid Enamel" I used to have a collection of colors of those paints.
I like to use SeaFoam from NAPA or WalMart for carbon removal. Carbon is a big issue and quickly expands groups with my .20 PPC and .204 Ruger rifles.[/quote]
Did you go to that link I attached? It appeared to be extremely thorough to me & there was absolutely no mention of Carbon. Below is only part of the article. Perhaps they don't know what they're talking about.
Examination of Gunshot Residue
Appearances of Gunpowder
All gunpowders are designed to burn quickly to produce rapid expansion of gas in a confined space. In an explosion something gets very big very fast. The burning rate of gunpowder can be classified in three categories:
Degressive (regressive) burning: gunpowder grains formed in flakes, balls, and sticks have a burning surface area that decreases continuously as the grains are consumed.
Neutral burning: gunpowder grains that are single perforated and the burning surface area remains relatively constant.
Progressive burning: gunpowder grains that are multiperforated and rosettes that have a burning surface area that increases continuously as the grains are consumed.
Unburned gunpowders can have recognizable shapes, colors, and sizes of grains. (Pun and Gallusser, 2007)
Composition of Gunshot Residue
Firing a weapon produces combustion of both the primer and powder of the cartridge. The residue of the combustion products, called gunshot residue, can consist of both burned and unburned primer or powder components, and can be used to detect a fired cartridge. Gunshot residue may be found on the skin or clothing of the person who fired the gun, on an entrance wound of a victim, or on other target materials at the scene. The discharge of a firearm, particularly a revolver, can deposit residues even to persons at close proximity, so interpretations as to who fired the weapon should be made with caution. (Dalby et al, 2010)
The major primer elements are lead (Pb), barium (Ba), or antimony (Sb). Usually, all three are present. Less common elements include aluminum (Al), sulfur (S), tin (Sn), calcium (Ca), potassium (K), chlorine (Cl), copper (Cu), strontium (Sr), zinc (Zn), titanium (Ti), or silicon (Si). A mercury-fulminant based primer may be found in ammunition manufactured in Eastern Europe and used in the Middle East.(Zeichner, et al, 1992) Primer elements may be easier to detect in residues because they do not get as hot as the powder. So-called "lead free" ammunition may contain one or more elements including strontium (Sr), zinc (Zn), titanium (Ti), copper (Cu), antimony (Sb), aluminum (Al), or potassium (K). Both titanium and zinc are commonly used in paints and can be contaminants, but the appearance of particles containing them can be distinguished from gunshot residue by SEM. (Martiny et al, 2008) (Dalby et al, 2010)
Detection of Gunshot Residue
The major methods for detection of primer residues are analytical and qualitative. Analytical methods include neutron activation analysis (NAA) as well as atomic absorption spectrophotometry (AAS) and inductively coupled plasma mass spectroscopy (ICP-MS). Scanning electron microscopy with energy dispersive analysis by x-ray detector (SEM-EDX) and atomic force microscopy (AFM) are used to identify the primer residue qualitatively. An X-ray analyzer can be beamed directly onto the particles visualized with SEM, so that the energy dispersive pattern can be generated, giving the elemental composition of the particles. For these methods, samples must be obtained from the skin surfaces of a victim at the scene. Delay in obtaining residues, movement, or washing of the body prior to autopsy will diminish or destroy gunshot residues. (Molina et al, 2007) A rapid loss in numbers of GSR particles occurs from 1 to 3 hours post firearm discharge, though maximum recovery times of 1 to 48 hours have been reported. (Dalby et al, 2010)
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I worked at a research facility at the University of Illinois for many years, not as a researcher, but as a machine shop supervisor & I worked closely with many researchers over the years. So I know darned well that equipment mentioned above has the capability to find Carbon if it exists in any amount. So, I can't fathom why wasn't in included in the list of residue? I do know it's in cellulose.
What we see looks like carbon to me too, but it wasn't on the list. Doesn't it strike you as odd?