Hawkins, et. al. ...
If you read carefully, you will see that I said 'about a thousand', which is a conservative number based on the nine years or so I've worked making barrels.
Traditional rifle barrels were/are not made by broaching, though many modern barrels are - the process having been first introduced on a mass scale about the beginning of WW2. Traditionally, the bore was drilled, reamed to size, and then rifled on a rifling bench or rifling machine which pulled a single cutter back and forth through the bore at the desired rifling pitch to cut one groove at a time until the desired groove depth was reached. The ancient rifling bench was usually used to cut a single groove at a time from start to finish, inserting a thin shim to raise the cutter to increase groove depth, the process being repeated for each groove, separately, and the work done by hand. The 'modern' rifling machines are designed to automatically index through the desired number of grooves, making a single pass at each and then raising the height of the cutter the preset amount for the next series of passes, again, the process being continued until the desired groove depth is reached - the machines being power-driven, of course.
The broaching process uses one or more 'broaches', which are very long cutting tools containing a successively larger- in -diameter series of cutting teeth, ending in the desired groove diameter, and machined on the rifling pitch desired in the barrel. This tool is driven through the drilled and reamed bore, and must also be mechanically rotated at the same pitch as the broach and finished rifling, since to drive it straight through the bore would not allow the broach to rotate, resulting in a larger bore, but no useable rifling.
The advantages of the traditional rifling machine are that it will accommodate any rifling design by making the appropriate cutter, and any rifling pitch within the range of adjustment of the machine - in the case of the Pratt and Whitney #1 sine-bar machine we use, any pitch between 0 and approximately one turn in five inches, infinitely adjustable (without fixed pitch stops, though with engraved scales as a guide), left or right-hand. The tooling is much less expensive and much longer-lasting (the typical broach costs thousands of dollars and has a finite service life due to the need to re-grind it to slightly smaller diameter each time it is sharpened).
While I did not say so originally (it being outside the scope of the original question), every barrel I made is hand-lapped: not to alter internal dimensions, but solely to improve interior surface finish by smoothing the remaining tool marks from reaming and rifling. My opinion is, that with modern barrel steels, you would lap yourself to death trying to achieve a taper by that method. The taper in the bore I spoke of is, as I said, an artefact of the drilling and reaming processes.
PRD1 - mhb - Mike