Details on barrel reaming with modern machines and tools.
by Charles J. Moore
During the pre-Industrial era, the job of reaming a gun barrel was a time consuming process. There were no reamers as have today. The gunsmiths of the period had only a few different types of scrapers at their disposal. Normally, two different kinds of scrapers were used to bring the bore of a barrel to the required internal dimensions and surface finish. The scrapers were run through the bore several times while being spun, usually by means of a hand wheel. Each pass of the scrapers through the bore brought the barrel blank an incremental step closer to being completed. While the process was rather labor intensive, good finished bore quality could be achieved simply because so little iron was being removed on each pass through the bore. Every so often, the gunsmith would pass a lead slug through the bore, and then measure the swaged diameter of the slug to determine when the barrel’s bore had reached the required dimension.
The first scraper that was typically applied to the bore was designed to remove scale from the interior of the barrel blank. Because early gun barrels were hot forged over a mandrel and then forge welded at the seams, all while exposed to the oxygen-rich atmosphere, heavy scale was formed inside the bore during the process. The same type of scale can be readily seen and felt on the exterior of a piece of hot rolled steel today. Scale contains carbides and other types of very hard compounds. These hard substances are quite difficult to cut and tend to dull cutting tools rather quickly. The scrapers produced to remove the scale were very simple in design and not intended to produce a smooth, uniform finished bore. The form of scraper commonly used for this application was an iron bar that had been hammered square and then twisted until the measurement across the helical corners was just over the size of the bore when it came off of the mandrel. The corners of the twisted scraper would break the scale free of the bore’s surface through shear abrasive action and brute force. Once the scale was removed and the raw iron exposed, the finish scraper could be brought into play.
There were two types of finishing scrapers employed to bring the bore to finished dimensions.
Read more in the November 2015 issue.