I shoot about 300 rounds a month of shotgun with plastic wads. Lots of plastic buildup.
I use gunk foaming non amonia window cleaner. Just fill the barrels up and let it sit for about 5 minutes then pull a bore snake or push a tornado brush through and the snot comes out like a black snake.
Leaves no rust or residue. For storage, I use the spray Tri Flow teflon lube on a bore mop and push it through.
Since the sabot is the same material, this should help.
OBTW, I use the gunk and bore snake routine with my Ruger vaqueros and my '73 winchester all shooting bp goex.
Sherrif Kings River Regulators
Hangman/Recorder ECV 1797
Crafter of Fine Ales
Fannie Mostly's Gun Boy