Some custom barrel makers now hone barrels after drilling to improve bore diameter uniformity and smooth the interior finish. This also reduces barrel lapping time. Since years, large-scale producers of hammer forged barrels have used honing. Smaller, “boutique”, barrel-makers are now using the process. This article explains the process of barrel honing. Watch the video. This video from Sunnen Products Co. will be an eye-opener for anyone interested in barrel-making. Barrel Honing Demonstrated. (Worth watching!) ):
Honing is a cost-saving and time-saving tool for custom barrel makers. A few minutes spent on a honing device can reduce lapping time by half, leaving an etched surface finish with a single-digit or low-double-digit Ra. The same process is used to manufacture diesel fuel injectors, where bore roundness and straightness are controlled to fractions a micron (0.000040″) with a surface finish Ra =0.15 uin (6 uin). The makers of button-rifled barrels are now paying attention to a key manufacturing process for hammer-forged cylinders. Precision bore-honing is the process. Honing produces an excellent bore surface quickly, which is crucial to hammer forging. (Why is honing important in hammer forging?) The surface finish of the barrel is the only feature that can’t be controlled when hammer forging. Surface imperfections in barrel blanks tend to be amplified when the blank is formed onto the rifling ring. If the bore is chrommed afterwards, imperfections will be even more apparent.) Honing improves bore diameter uniformity, accuracy, surface finish, and roundness along the barrel. It can be used as an alternative to a pre-rifling lapping. The direction of the finish line in the bore is the main difference between a honed and lapped bore. The lines in the bore are left with fine spiraling crosshatch, whereas a lapping leaves lines that run longitudinally. If desired, the manufacturer can remove crosshatch finish after rifling with a quick lapping. Honing is fast and accurate. It can also be automated. Its surface geometry and quality can be used to duplicate lapping except for the longitudinal lines. Frank Green, Bartlein Barrels, told us in 2015: “We worked closely with Sunnen to test the prototype machine. The machine works perfectly! We ordered and received… a new machine manufactured with the changes we desired on it, and [subsequently] purchased a second one.”
The Sunnen hone is used to secure the barrel blank into a 3-jaw clamp. Honing oil is pumped in at one end, while the tool operates from the other end. Sunnen’s Long Bore Tool utilizes metal-bond diamond superabrasives or CBN to remove reamer marks and other imperfections caused by upstream processes. Sunnen states: “Honing can be used as a replacement for hand-lapping before rifling. It removes surface waviness and reamer scratches quickly without the need for labor-intensive hand-lapping. Honing produces a consistent bore size (+-0.0001″ or less), parallelism and roundness, and surface finish from end to end. This results in a consistent groove depth. The ideal bore geometry reduces distortion in the bullet shape.”
The use of computer-controlled, advanced honing machines allows for a high degree of precision when honing. Sunnen Products Company has a machine that is advanced for barrels from.17-.50 caliber (see control panel below). Spindles on the machine can correct imperfections in bore size so small that only an air gauge could measure them. This consistency allows for improved bore uniformity which in turn produces more accurate barrels. Sunnen Products Company is the world’s largest vertically-integrated manufacturer of honing systems, tooling, abrasives, coolants, and gauging for precision bore-sizing and finishing. Sunnen’s clients include manufacturers of diesel engines, gas engines, oil field equipment and gun/cannon barrels. Sunnen employs over 600 people in its global operations.
