Three or four commonly-found interpretatons which may or may not apply to gunmaking but are thought-provoking.
1) freehand application of tool unjigged, untemplated, uncontrolled except by eye and hand, tolerances of assembly of parts terrible to irreproachable but no consistently repeatable, "interchangable" or identical copy produced with relation to a model or blueprint. Does not preclude layout on material, from rudimentary to painstaking. Cut and try accompanied by the old Masonic standards of comparison, i.e. "plumb of truth, square of integrity" etc.
2) applicaton of tool or cutter in a linear or reciprocating manner "by hand"; the operation of most chopping, chiseling, shaving, scraping tools. When linear or reciprocating motion of the human hand and arm is applied to a device (say crank and flywheel) which produces continuous rotary motion in the cutter or material cut (by this standard a treadle or bow lathe and even a carpenter's brace is very much a machine) it's no longer precisely "handwork" in the sense of #1 above no matter how demanding of power by Armstrong. I know there are apparent exceptions for instance metal planer or the big gang or frame saws still used to resaw sandstone. However, most of us, whether we think much about it or not, recognize that the conversion of energy from sources other than human muscle into usable, controllable, and endlessly reiteratable motion in a toolhead (the "drivetrain" so to speak) is the hallmark and bedrock of the industrial revolution. How many gun barrels were ever bored without a crankshaft in the boring rod? Just because it's accomplished in a grimy, ill-lit smithy doesn't make it "handwork".
3) many techniques, skills and processes under the mastery of one mind and one set of hands; the one-man-band, backswoods prodigy idea which is very long-lived and attractive to the individualistically-inclined. As we've seen, wasn't true in Birmingham and probably very little truth to it in any era. Complex processes require complex organization.
4) perhaps most relevant to gunmaking, finishing and fine fitting as in blacking down and polishing, exterior sculpting and surface adornment (checkering, engraving). Whether this work is 90% of the work in a built-by-hand gun, I leave up to you. You can engrave an iron-pipe zipgun, but a highly-organized and specialized industry had to make the pipe.
jack
