Cylinder and Slide specifies .005 as the closest they will go as it is a standard maximum allowed for reliable functioning but not so close that unforeseen thickening from shooting and use could bind and cause sketchy reliability.
I could live with .004 though. I think barrel-cylinder gap is a necessity for efficiency, but .002 could be too tight for a double-action revolver. The single-action revolver on a true and fixed axis can handle those tight rotation tolerances, especially if it is a BFR or Freedom Arms model. The swing-out cylinder yoke could cause enough play to build-up so that the .002 span could bind and inhibit rotation of the cylinder when engaged. Just my thoughts on the matter.