gbflyer wrote:I've seen pictures of gun drills but I'm not sure how they work. We need to get Spinner2 over here from SC.org to school us.
Barrels come with the bore and contour already done. All that's left is the threading and chambering. The chamber reamer is the shape of the cartridge but made with cutting edges out of high speed steel.
Gun drills typically are either a HSS or tube formed blank, with a carbide single flute head brazed on. There are special gun drilling machines, which have a spindle that counter rotates from the drill spindle, and there is a drill bushing that goes between the two to guide and support the drill while rotating and feeding.
Alternatively, you can actually gun drill without a gun drilling machine, by starting with a pilot hole that is about .0002-.0005" (not a typo) oversize from nominal, and about 2.5xD deep to act as your guide bushing. I do this a lot for drilling waterlines in mold bases.

