The cutters are narrow bars of steel, having upon one side three diagonal protuberances of about one-sixteenth of an inch in height and half an inch in width, ground to a very sharp edge at the top.  It is these which produce the rifling.  The three cutters, when inserted within the iron cylinder, form upon their inner surface a small cavity which decreases towards the top.  Into this is inserted a small iron rod attached to the machine and revolving with it, but so controlled by a connecting cog-wheel that the rod is pressed at every revolution a little farther into the cavity between the cutters.  The effect of this operation is to increase the pressure of the cutters upon the inner surface of the barrel, and thus gradually deepen the corrugations produced by the rifling.  The rods make twelve revolutions in a minute, and it occupies thirty minutes to rifle a barrel.  There are twenty-seven of these rifling-machines in constant operation day and night.  This process is the last which takes place within the barrel, and it leaves the bore in a highly polished and brilliant condition.

Among the innumerable machines which arrest the attention of the visitor by the beauty and grace of their operations is the broaching-machine.  This is designed to cut out and polish the inner surface of the bands which encompass the barrel and stock.  These bands are irregular in shape, and cannot, therefore, be bored out as the barrel is.  When they emerge from the drop, or swaging-machine, they are somewhat rough both interiorly and exteriorly, and then undergo a series of operations which leave them in a highly finished condition.  The first of these is called broaching.  A cavity is made under a huge press in which the band is placed.  The broach consists of a steel tool about ten inches in length, and of the exact diameter and form of the interior of the band, and is armed upon its entire length with concentric rings composed of very short and sharp knives.  The broach, being placed over the cavity of the band, is slowly subjected to the pressure of the two-ten press, and is thus forced completely through the band, cutting it out as smoothly and easily as if it were composed of lead.  The bands are then milled upon the outside by a process called profiling, drilled for the rings, placed upon mandrels to insure the exact shape required, filed, polished, case-hardened, and thus finished.

The hammer passes through a great number of processes before it is completed.  It is first forged, then dropped, trimmed, punched, drifted, milled, turned, filed, and lastly case-hardened.

The cone, although one of the smallest pieces in the musket, is yet one of the most important, and requires a great many separate operations in its manufacture.  It is first struck in a die, then clamp-milled,—­passing through a machine having clamps which hold short knives that shave the entire outer surface of this very irregular-shaped piece; then the thread is cut upon the screw, and both ends are drilled,—­this process alone requiring fourteen separate operations.  It is then squared at the base and case-hardened.