Try the JB compound but not the steel wool. I had a rust spot in my Knight barrel too. The JB didn't take it out.
But I found a simple non-abrasive solution. Get a can of Evaporust, remove the breech and plug it up (I used a rubber cork from the hardware store), and pour the Evaporust filling the muzzle. Don't get any on the outside. If you do wipe it off.
Let it set in the barrel overnight (24 hours). Pour out and swab the bore. Your rust will be gone.
PS: make sure your plug is not leaking because the Evaporust may remove or tarnish the bluing on the gun.