Fire lapping is a last step, taken in desperation, with no going back. There are several things you can do before resorting to fire lapping.

First, stop using the stainless steel wool or any stainless steel bore brushes.  Those have wrecked a lot of otherwise OK barrels. If the grooves are packed, they are probably filled with some combination of dirt,dried-out oil & grease.  Get a sturdy cleaning rod and several good bronze wire bore brushes in the .27 to .30 size.  Start from the breech and scrub the barrel dozens of times.  Follow that with some patches.

To go further, take the barreled action out of the stock.  Things will get messy.

Next, fit a rubber stopper in the muzzle and fill the barrel with some good penetrating oil or grease-cutting solvent.  Prop the rifle up vertically and let it sit for a day or 2.  Then repeat the bore brush & cleaning patches routine.

Next, find one of those electrolytic cleaning sets.  Put the rubber stopper back in the muzzle and fill the barrel with ammonia. Household NH4OH works, commercial grades work better.  The electrolytic cleaner has an iron rod with a couple of rubber o-rings to keep it from touching the barrel. Use a DC low voltage power source, probably from some old electronic gizmo that failed long ago.  Use alligator clips.  Hook one wire to the iron rod and the other to the barrel.  The idea is to plate the iron rod with all the crap adhering to the inside of the barrel or get the crap suspended in the ammonia solution.  Allow the current to run for 10 minutes or less.  Drain out the ammonia.  Repeat until the ammonia comes out relatively clean. If this does not seem to be working,try reversing the leads.

After that, you need to neutralize the ammonia.  I fill the teakettle with water, bring it to a boil, and slowly pour the water down the barrel, from the breech to the muzzle.

Then go back to the bore brushes and patches.  By now, the barrel might be as clean as it is going to get.