I also had a very tight fit with the .550's + .015" cotton patches...couldn't thumb start them, but they would punch in with a healthly palm of the hand on a short starter.
I'll try some .530's + .018" prelubed pillow ticking too, as I have both on hand, see how they do...if they don't do any worse than the .550's & .015", at a minimum they'll be easier to load.
And it'll make shooting the .56cal more convenient from a supplies point of view, not having to find and special order .550's, etc