Making and Knowing
A minimal edition of BnF Ms Fr 640 in English Translation

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How to adjust a bent gun barrel

Take off the breech and put it [the barrel] on a well—leveled table set perpendicular to the floor, and insert a very smooth string without knots, on each end of which there is a plumb hanging from each side. Then look in the barrel along the string, and if it does not touch equally all over, note the place where it does not touch and hit it with a hammer on the exterior of this this side in the same place, and this will make it straight. Do this all around it.