There are degrees of cleaning, regular maintenance, slightly abused, and completely ignored bores. Also, calibers with powder amounts and types come into play. Shooting a 223 presents different fouling tendencies than say an F Class 308 barrel where a guy does not like to clean.
An example of an abused, cleaning wise, Krieger 308 barrel that I bought for cheap money off this site, which had cooked on carbon from front to back, SOLID BLACK lands and grooves. This F class barrel was shot hot as hell, NEVER cleaned properly. The Throat looked new when I got the barrel, but I had never seen a barrel carboned up as bad as this barrel. After pushing 6 wet patches then brushing the barrel, I kept looking at the Blackness in the barrel off and on for about two weeks, thinking how in the world did someone ruin a barrel like this?
I tried soaking with wipe out products for a week, patching out every day, with a re soak and brushing, always using Accelerator, then try their Tactical...all to no avail.
Then I went to C4, soaked over night, then wore out a new bronze bristle brush, with the end result, still black from end to end. I repeated brushing and soaking everyday. I would brush for 25 strokes, then another day of soaking. I used a new bronze bristle brush away every 100 strokes. I had bought three 16 oz bottles of C4 after reading posts on this site, obviously drank the Kool Aid. This process went on for 7 calendar days, the cooked on carbon showed no hint of getting thinner.
Then I saturated 5 patches with JB, short stroking the patches in the barrel on a tight fitting punch type jag. This process removed nothing or next to nothing with only the slightest hint of metal starting to come through in tiny spots about the size of a straight pin head. I figured the barrel was probably going to end up a piece of trash.
Next, I brushed again with JB, 25 strokes with a new brush, wet patched out, then dried the bore...Hawkeye showed only a hint of carbon coming out. In frustration, I put new batteries in the Hawkeye, re-focused the eye piece, and cleaned the mirror. I was ready to sling something up against the wall. I decided to use some Isso, then Flitz. I could see the very slightest amount of carbon starting to come out, but not uniform removal, looking like specs of carbon coming out.
If you go back and read my first post, you will see how I got the barrel back to new condition. It did take three, two week sessions of soaking with brushing in between. After the FIRST two week soaking, it was all too obvious that the carbon was coming out. After the third soaking and brushing, the barrel looked as carbon free as a brand new barrel.
With a long Grizzley rod, I checked the bore uniformity, and it was .3000 from end to end, Krieger made one hell of a barrel!
I cut the old chamber off and used a reamer with .090 FB, it is shooting the 155g Palma in the 2's at this point with only 21 rounds on the new chamber in brand new unsized Lapua brass with 44.0g of R#15, with WLRM primer shooting the smallest group of the primers I tried. No group was over 3/8" that I tried with powder charges ranging from 43.5-44.5 in .5g increments with 4 different primer brands used at 44.0g. Again, Krieger makes one heck of a barrel.
It will take further experimenting to see if brushing with a super penetrating oil is an answer for regular cleaning intervals for carbon. The use of penetrating oil may take time to work "under" the carbon. It was obvious that good brushing was needed in between soaking, and that the carbon was getting gooey.
If I had the GM Top engine cleaner that Bill recommended, my cleaning would probably have been a lot easier.