Another translation on the text Drew posted above:
The next operations take place at the factory and consist of enlarging the bore of the barrel by drilling out the chemise with the aid of a square bit. The barrel is placed on a drill bench and held in a kind of vise, while a square bit mounted at the end of a block operated by a hydraulic wheel, turns in the bore and removes the chemise, which is fully welded to the barrel.
To make a good barrel, the thickness of the chemise inside the riband must be considered, so as to ensure the removal of the chemise. For example, a gun that will be finished to a 17mm diameter bore size; it will have to be final forged on a mandrel of 12mm with a chemise of 1 mm thickness, which adding the thickness of the chemise times two, equals a total of 2mm. During forging, the thickness of the chemise is not reduced, but is instead thickened, by about 1mm. Under these conditions, drilling the bore with a 15mm bit would be enough to remove all of the chemise from the bore. (12mm mandrel + 2mm for the chemise + 1mm for thickening of the chemise = 15mm) Drilling the bore to 17mm would remove another 2mm of material from the bore, which should be sufficient to straighten the "meandering hole" and to give the interior a good finish, which is necessary and sufficient.
Last edited by Steve Culver; 10/04/12 10:19 PM.
