How did gunsmiths rifle guns in 1776?

The rifle barrel was bored out, and a long wooden rod with a steel tooth was inserted into the barrel. This rod had a spiral cut in the outside, that when drawn back and forth, caused the rod to twist. The steel tooth was on a small hinge, and was raised by slipping bits of paper under it to cause it to cut into the steel of the barrel- and each groove required hundreds of passes in and out of the barrel. This was slow and labor intensive- which is why rifles were more scarce than shotguns, and very expensive.