I took the advice of Cayugad and several others and started using the felt wads with my 50 cals and my 54 cal. using conicals and PRBs. I would have to say that my accuracy increased by 50% or better. I suspect there are several reasons for the increased accuracy. Which may include more consistant pressure and reduced fouling. Who knows why but I won't shoot my MLs without them now.
I picked up a bunch of 50 and 54 cal wads at a gun show a few months ago for $3 a bag of 100. I got all the guy had.