You generally do not clean an airgun barrel. One initial cleaning when the gun is brand new, may be all you ever need. It is better to under clean, than over clean. Depending on your equipment you can damage the rifling or more important the Crown (the very end of the rifling, as you exit the barrel).
The only reason to clean a barrel is if you feel the accuracy has been reduced from what is normally expected.
Do not use an uncoated steel rod or steel brushes inside a steel barrel, a brass rod is fine. If it is a Brass Benjamin or Sheridan, use a plastic "pull though" fishing line or use a wooden rod to push a patch through. A one-piece aluminum cleaning rod may also work. There is even less reason to clean a Benjamin, just leave it alone.
Use only clean dry "cleaning patch" of the proper size.
All of our PCP guns that have a Magazine have an internal O-ring in the barrel; care must be taken to not damage this 0-ring. We suggest using only a" pull though" type and start at the muzzle end. Only use a dry patch.
What not to use: Do not use any firearms gun cleaning solvents. Do not use silicone oil.
Some have reported good results using Ballistol or Simple Green as a cleaner. We have not tested this on all our guns so we are hesitant to recommend it. It's best to stick with the dry patch.