If you really feel compelled to clean out a gas tube, my recommendation is to remove the gas tube and immerse it in a good carbon solvent in a vibrating cleaning tray and leave it there for about eight hours.
Take it out of the vibro-tank and use compressed air to blow the tube clean shooting the air in from the breech side of the tube.
Carbon deposits mainly accumulate in the first three to four inches of the gas tube at the gas port side.
Very little carbon residue actually adheres all the way back to the breech face end.
Shoving a pipe cleaner into the breech area of the gas tube will just shove what carbon residue there is in that area into a mass four or five inches up the gas tube.
Gas flow is now restricted at the gas port area of the tube and again about five inches down the tube.
Rifle starts malfunctioning and owner can't figure out why,,,,,,,
If you really think your gas tube is fouled out, the things only cost about $10.00,,,,,it is easier to just replace the gas tube.