yes a bit to much science and not enough expirence on the ground is right.
getting to a few microns means cutting tools are changed a lot, often during process, and many passes of the tool over the steel, all of this means time. especially machine time on a machine that has to pay for itself as well, so it is possible to do so, but that actually means higher prices on the base product and still you have to use the files in the end as no machine can replace the gunmakers hand and eye in the end process.
the same goes for barrels which is a highly specialized part of gunmaking, most these days are cold hammer forged to very tight internal dimensions and afterwards the outside are machined to near the final size, it is then mounted in the monoblock and then struck up with the files for the final surface profile, but it is only when the files are in motion that you get the perfect end result as it is the eye that tell's the gunmaker where the final strokes is placed, and we have no replacment for the eye yet

best
peter