My personal feeling, and I have no proof, is that "seasoning" is done on iron, and not on todays modern steels.
I actually think that those of us who bought into the seasoning theory were actually removing little minor manufacturing imperfections from the barrel through repeated shootings and cleanings....I don't think, even for a minute, that we season a barrel in much the same way we season an iron skillet.
Now for the meat of your problem...removing "gunk" from a rifle barrel can certainly be a chore, and not an easy one.
I use a brass brush and Kroil, from Kano. Then I use Hoppe's, and lots of it. I have found, over the years, that repeated, good, indepth, cleanings as I just mentioned, will, in all probability, clean up a barrel that seems at first to be a total waste.
You don't necessarily have to clean it until it squeaks the first, or even second time. But if you will agressively attack that barrel each time you shoot it, you will eventually see a big difference.
And, of course, you can't forget the grease, elbow grease, and don't use it sparingly.
Also, don't forget, you're dealing with a piece of steel, and steel can sometimes be as tough as.....well, as tough as steel.
I'm sure others have methods that work quite well too, and I'm equally sure you're going to get a few more opinions.
Either way, good luck on getting the barrel clean.
Uncle Russ...