I shoot a lot of plastic out of my inline rifles. Not as much as Sabotloader of course. But in all my shooting I have never really had a build up of plastic, copper, lead, etc.

A good bore solvent is Birchwood Casey Bore Scrubber, Butch's Bore Solvent, or Hoppies. All of them will take the plastic out of the barrel and any other kind of fowling you can think of.

If you go the oil route, just simply swab the barrel with isopropyl alcohol before loading for the first time. Then a couple dry patches. That will remove any oil, or crud in the bore and make the rifle ready for loading. Also pop a cap or two through the nipple to make sure that the fire channel is nice and clean.