Poppy, I think your rollers are too close together. It should not be
that difficult to turn the handle. Try it again, put the stack (paper,
silver & brass) between the rollers and close them just so that you
have to tug a little to remove the stack. then turn the handle a 1/4
or 1/3 of the way around to close the rollers just a bit more, and
roll the stack through.
Goss Design Studio has a wonderful web site which contains a page
just about roller printing. I was surprised to see their directions
were enclosed with my Durston rolling mill when I opened the box.
Durston obviously endorses their methods for roller printing.