So, the patch comes out black...but is it carbon? Based on comments from this forum, I recently purchased some Free All penetrating oil, which has been touted occasionally as an effective carbon remover.
For starters, this is my standard cleaning regimen:
1) Wet patches of Bore Tech C4 until very little carbon is coming out, 3 strokes w bronze brush, patches of C4 until very little carbon is coming out, 3 more strokes w bronze brush, more patches of C4 until no carbon is visible, then three dry patches.
Note: FWIW - even this rather extensive treatment using C4 leaves a substantial amount of carbon in the throat and first few inches of barrel as observed using a borescope.
2) 2-3 wet patches of Cu+2 Copper remover>>>~15-20 min, repeat 3-4X, then three strokes w bronze brush, 2-3 more wet patches of Cu+2 until no more blue color can be observed, then thee dry patches. I follow this with a couple patches lightly wetted with plain tap water to help remove any remaining Cu+2 residue, which is fairly "sticky" even after the dry patches, followed by three more dry patches.
Note: Readily observable amounts of carbon will be removed by the Cu+2 patches, noticeably the first two, and again following the bronze brush treatment. This is carbon that was not removed by the C4 treatment.
3) Two patches of Kroil Penetrating Oil>>>left overnight at this usually, then a couple more Kroil patches in the morning, three strokes with a bronze brush, a couple more patches of Kroil, then three dry patches.
4) I finish with one patch of Hoppes Gun Oil, followed by three dry patches.
Free All Treatment
Note: the following image showing patches following treatment using Kroil overnight/bronze brush strokes, then by Free All/bronze brush strokes was done after the above standard cleaning regimen, on a barrel that only had a couple hundred rounds through it, and only had the very teeny tiniest amount of hard carbon residue visible via borescope in the throat region.
First, neither Kroil nor Free All by themselves removed much if any carbon, as nothing was visible on patches #1 and #3. However, as shown in the attached image, treatment with a bronze brush and Free All removed a significant amount of dark gray material that LOOKS like carbon (patches #5-7). I should point out that when observed up close, the dark gray Free All/bronze brush patches don't look exactly the same as carbon removed during the first cleaning step with C4. It's difficult to explain how they look different; the difference is subtle. Nonetheless, they do look a little different. I'll come back to this later.
As I had observed in the past, O/N treatment with Kroil followed by the bronze brush seemed to remove only a very small amount of carbon that was visual on patch #2. Noticeably, successive treatment with Free All and the bronze brush removed what appeared to be a lot more carbon, which is clearly visible on the patches.
My initial takeaway from this experiment was that my standard cleaning process was leaving a LOT more carbon in the barrel than I had previously believed. However, I was a little suspicious for the following reasons: 1st - the fairly extensive standard cleaning process prior to using Free All, 2nd - the relatively low round on the barrel, 3rd - the fact that the dark gray color coming out on the patches did not seem to lessen in intensity even after four successive treatments.
My thought at this point was that maybe the bronze brush was leaving a small amount of bronze material following contact with the inside of the bore, and that this material was somehow interacting with some component(s) of the Free All to generate the grayish color. Recall I mentioned previously that the dark gray Free All/bronze brush patches looked subtly different that typical heavy carbon fouling in the preliminary C4 Carbon Remover cleaning phase. At some point, most of us have observed what is commonly referred to as a streak test where different materials leave a colored streak when rubbed across a ceramic tile. I wondered if something similar to this might be going on with the brush and the Free All, rather than admitting to myself there might really be that much carbon left in a relatively new barrel following what I consider fairly extensive cleaning, without resorting to the use of abrasives.
I thought about this for a bit, then decided to go one step further repeat the Free All/bronze brush treatment on a barrel blank that had never been fired. Surprisingly, the patches came out pure white, with no dark gray color at all, even after two successive treatments (not shown).
I am still not certain that the dark gray coming out with Free All/bronze brush treatment is actually carbon. As I mentioned, there is just something about the appearance that doesn't seem quite right. Nonetheless, if it actually IS carbon, then it is clear evidence that common cleaning treatments leave a pretty substantial amount of carbon in the barrel, short of resorting to using abrasives. If the material on the patches is NOT carbon, I am at a loss for another experiment that would clearly demonstrate this. Frankly, it doesn't matter that much to me anyhow, but I hate to leave an experiment uncompleted. I continue to use the Free All/bronze brush treatment following my standard cleaning procedure, maybe every 2nd or 3rd time I fire a particular rifle. I figure that even the material coming out on the patches is not carbon, I doubt the Free All/bronze brush treatment is doing anything to harm the barrel.
The general take home message(s) from this should be that first, many of us using common barrel cleaners (i.e. not abrasives) may not be getting our barrels as clean as we would like to think. Secondly, just because something doesn't show up on patches during a particular cleaning step doesn't necessarily mean the barrel is "clean" and it has all been removed. A cleaning step may only remove a certain amount of material after which no more comes out, even though there is still some remaining in the bore, until a different cleaning step/material is used. Finally, interpreting the meaning of dark colored material that comes out on patches may not be quite as simple as it seems. Of course, none of us wants to see dark gray patches come out after we think we have the barrel relatively clean. But any dark material, carbon or otherwise, often shows up like a spotlight in the dark when it comes out on a pure white patch. Regardless, each of us has to decide for themselves how clean their barrels need to be, and to what lengths we will go in the cleaning process. I am not advocating for or against any particular cleaning process in this post, merely sharing a few observations I have made.
. I keep patching until they're clean. 
