I've discovered many times that Hoppe's doesn't get carbon out of the chamber or breech very well. What is a good product for this as I've scrubbed laboriously with Hoppe's and a toothbrush and/or bore brush with limited success.
I use a 40 caliber bronze brush(for 38/357 chambers), I had heard other members on this forum recommend wrapping a 22 cal brush with scotch bright, Flitz on a patch, soaking the cylinder, using a Lead-Away clothe, and many other chemicals. Many of the methods mentioned work. The bronze brush and Hopes works for me.
M-Pro 7 (Pantheon Chemical) was initially developed for cleaning military artillery canons that develop heavy carbon build-up. It works fast with a minimal amount of brushing.
Sometimes you just need to let your bore cleaner sit for a while. Load up the barrel and cylinders with your bore cleaner, work on the rest of the firearm, then go back 15-20 minutes later to scrub things out and see if that doesn't help.
Try the Brownell's bronze brushes instead of Hoppes or Outers brand. I find that the Brownell's is just a little stiffer and therefore a bit more aggressive on fouling. If that doesn't do it, get yourself a treated lead remover rag sold by a few of the Companies. You can also try a Lewis Lead Remover.