Although the copy of the page above is a bit "cloudy", the arrow pointing to the action/barrel flats in figure 2 reads .002" to .004" clearance between the flats of the barrel and the action body at this point. This is a statement from the famous Birmingham gunmaker Robert "Bob" Turner. He further notes that the clearance between the circle of the lumps and the draw of the action is .0005" to .00015".
The clearance is for shotguns, not double rifles. Twice as much clearance between the barrel/actions flats and rubbing between circle and draw for double rifles.
Stephen Howell
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