This seats against a steel plunger within the tube that has a coil-spring in front of it.
The front end of the cutter is beveled back from the top at about ten degrees. The end of the
spring-backed plunger is beveled at ten degrees in the opposite direction, so that its included angle
with its top surface is 100 degrees. The front end of the cutter is held upward against the top surface of
the rifling head. The cutter is normally about 2 to 2 1/4 inches long over all and the rifling head 6 to 8
inches long depending on the caliber. The top or cutting edge of the hook is cut on a radius to fit the
bore.
The cutting edge of a rifling cutter is ground and honed to a template. When it is resharpen or honed
during the rifling operation its form will not be changed at any point. The cutting edge has to be kept very
sharp and very smooth to do a good job. The barrel steel is tough and tends to tear, rather than cut
clean, unless the tool is kept sharp.
The scrape-type of rifling head leaves a better finish in the grooves than does the hook-type hut it is
more difficult to keep sharp and requires very careful honing to do a good job. Its cuts by scraping rather
than a shearing cut and the shavings are fine.
The rifling head is a hollow cylinder, and is made of high-carbon steel with a slot for the cutter cut
lengthwise, about two inches long, on one side. The port has to be cut very accurate, as the scrape
cutter must fit it closely with no movement. The cutter cuts in both directions while traveling through the
barrel. The rifling head is about 6 to 8 inches long and is threaded internally on both ends. There is a
thread at one end for attaching the pull tube, which is used to carry a supply of oil to the cutter.
On the other end, a fine thread is used for the adjusting screw to raise the cutter. In the bottom of the
rifling head between the port for the cutter, and on the opposite side, the fine threads for the adjustment
screw, a narrow slot is cut length-wise of the head. This is for the head of a screw to set in which is
screwed into the bottom of the adjusting wedge.
The cutter body is fitted very close in the slot in the rifling head and the bottom of the cutter body is
ground on a taper of about ten degrees from one end to the other. The front edge of this taper is at an
exact right-angle fit to the sides of the cutter body. The cutting edge of the scraper on top of the cutter
body is not cut at right angles to the sides of the cutter body and rifling head. It extends across the top of
the cutter body at a forty-five degree angle to give as much shearing effect to the scrape as possible.
The scraper is at the central point of the cutter body and the body of the cutter is cut away at each side
of the scraper to give chip space. The edge that does the scraping has an included angle of eighty
degrees, and the sides sloping down and away from the edge equally in both directions to the top of the
cutter body. This scraping edge also has the contour of the circle of the groove diameter of the barrel.
The edge should be ground and honed to a template. By doing this its shape will be true and will remain
so. The template is cut from thin 01 tool steel.
The wedge, which raises the cutter in its slot in the rifling head, is turned with a circular contour on the
bottom to fit the contour of the inside of the rifling head. The top of this wedge is also ground off on a
ten-degree taper to match that on the bottom of the cutter body. The thickness of the wedge has its thin