"I shot many 38specials. And as a newb I didn't clean it well. The carbon rings in the chambers are about fossilized. Brass brushes, every solvent I could find, nothing gets it clean. What do I do?"
You've said quite a lot here.
You didn't clean it well. As noted,, most of us do clean our guns in a manner to prevent carbon buildup.
What to do.
Field strip the gun, (basically removing the cylinder.) Find a container that will hold the cylinder, and immerse it in a good cleaning solvent. Start with Ballistol. Soak for a few days,, THEN use the drill & bronze brush. After a good scrubbing,, return the cylinder to the Ballistol. Let sit for a few more days. Repeat a few times. It takes TIME to allow the solvents to penetrate the carbon buildup. You can also switch around a few different solvents to create a differing cleaning effect.
Now,, I had a gun brought to me years ago with a bad carbon ring buildup. Since the owner had shot both jacketed AND cast bullets,, I did that a few times,, then I went for the Outers Foul-Out system. It took about 6 times of allowing that to work. Each time,, it took longer for the system to load up & require me to clean the rod. After it sat for almost 2 hours & still didn't load up, I switched back to Ballistol. A few more times of that,, and the .357 was back to CLEAN chambers.
While that may SEEM to be an option, I'd reserve that for a very last resort method. UNLESS,, the throats are undersized or out of round. Then honing would correct the chambers AND clean things. Sometimes the gunsmiths who hone chambers, may use a cutter that's too big UNLESS you specify the problem & do NOT want the chambers opened any further.