I've never had a problem with plastic fouling from sabots, even when shooting very hot loads from my Savage with no between shot swabbing. Never even a trace of plastic left behind.

As fas as hot water cleaning goes, you really don't need to soak the barrel at all. If the barrel can be removed from the action and the forestock removed from the barrel as well, then all you need to do is immerse the breechplug end, with the breechplug installed, into a bucket/sink/bathtub full of the hottest water you can work with and a squirt of dish soap (bucket recommended if you're married or you'll likely have a very unhappy wife! ). Then take a bore mop (or cleaning jag with a snug patch if you don't have a mop) and pump it through the barrel repeatedly. This will create enough suction to draw water into the bore (like a well pump) and will blow the water out of the breechplug with each stroke. I used to use this method with my sidelock rifles after shooting both real BP, Pyrodex and T7 with outstanding results. Just be aware that you'll need to let the barrel and breechplug dry completely and then carefully apply a preservative (I use Breakfree CLP) to ALL surfaces because the hot soapy water will completely degrease the barrel and the bore will rust quickly. But this method is the fastest and most thourough way to clean a BP rifle.

Mike