Off the wall:
Soaking as advised above, lets the chemicals do the work for you. Just requires time and patience. Kerosene, mineral spirits, Krol penetrating oil can do the job.
Once 'clean' (since these are VFW rifles, and probably used for firing blanks), I'd finish with Wright's Silver Cream. It's a paste that not only polishes the barrel, but
also cuts down the cleaning time after use.
I first learned of it while at the PD academy. We were carrying the S&W M66. Always got dinged at inspection, because of the 'dirty face' on the cylinder. Used Wright's
and the black disappeared. It also made subsequent cleanup a lot faster.
"No man's life, liberty, or property is safe, while Congress is in session." Mark Twain