I would rec. a synthetic oil. I beleive that regular gun oil could damage the o-rings. Many PCPs are difficult to remove the barreI. I have to remove the shroud on my Marauder to clean the barrel. All my other rifles, I don't, however, if you have a bolt action, it can be easier to clean by removing it.
The barrel that requires the most cleaning is a Hammer-forged. It has the most micro-pitting incorporated in the forging process. After about 150-200 shots, I lose accuracy and have to clean it. If it has been a while, I will run a few lead cloth patches first and follow up with cleaning patches lightly sprayed with Synthetic oil. I rec. that you don't run a dry patch but leave the barrel oiled after cleaning. A dry barrel can lead up faster. I have been told that shooting a "dry" barrel could permently alter the accuracy of your barrel ( or take an expert gunsmith to correct). Not trying to start an argument with this statement, but it is easy enough to leave the barrel oiled, and fire a few primer shots before I start shooting seriously.
Smooth-twist and Lothar Walther barrels require less cleaning. The opinion on maintenance for these barrels varies greatly. That said, if the rifle loses accuracy, that is the first thing I would do. Because you are not shooting powder, air rifles require less cleaning. I have several rifles with a Lothar Walther barrel and when I attempted to clean them after 200 shots, nothing showed up on the patch. I do however, wipe the outside metal with a oil patch after every use and clean them all prior to putting them up for the winter.
hope this helps.
NM