One persons 0.004" is anothers 0.002" or 0.006". To get the "feel" of the feeler gauge go get your mike and set it to 0.004" and drag your feeler gauge through the anvil , then you can get the feel of what 0.004" actually feels like.
The Wesson's I set up at 0.004" wound up binding after a couple cylinders full of mild .357 loads at a fairly fast clip . Seems like the barrel which includes the forcing cone heats up and expands faster than the cylinder. Backing the gap off to 0.005"-0.006" works a lot better . Also high primers dragging on the recoil shield can force the cylinder into the barrel if there is any end shake, ditto with dirty chambers not letting the round rest against the rim.
So for reliability in defense revolvers make sure to try the cylinder gap setting on these gun before relying on them.