Don't have Rice, but had a 42" Goodioen barrel with 48" of twist. It liked 65gr. 3F or 75gr. 2F for identical accuracy - both using a .395" with .020" to .0215" both denim or a .400" ball and .019" to .020" denim patch, also with LHV lube. Last spring, it showed it liked 55gr.2F with the .395" ball and spit patch. Later, in hot weather, it refused to shoot that load as accurately as I demand.
Rich- with round bottomed rifling, you are going to need more patch to fill the grooves, than anything you've used so far. Do the math - with a .400" bore and normal .016" depth rifling, you have a groove depth of .432". Shooting a .395" ball will require at least a .0185" patch to get to the bottom of those deep grooves and that's without any compression. I usually find burning of the patch with such a thin combination. I suggest you use any normal pure 100% cotton ie: denim or ticking, that measures at least .020". That is 8 pound denim. Some makes are .020" (by my measure) and others run up to .0215". The tighter the better as far as accuracy goes. Once into the bore, they all load easy with spit, LHV or Hoppe's Plus. A perfect crown in the muzzle allows easy seating of the ball. A too-sharp crown makes seating difficult.