New Furnace Success with Millennium Manufacturing
91´«Ã½ Technology Center has been busy for the last two years developing a vacuum gas nitriding process.  This work has culminated in a new Solar Manufacturing furnace built to 91´«Ã½ exacting specifications.  HT-81 is now on-line, providing customers with a new and innovative process.  Combining the benefits of the vacuum furnace with the surface hardening benefits of the gas nitriding process, this furnace shortens the process cycle time to produce cleaner parts in less time and with better results than traditional equipment.
Shortly after HT-81 was brought on-line, an excellent application for the furnace was brought to Solar by Dave Fricke, President of Millennium Manufacturing. Â Located in Quakertown, Pa, Millennium Manufacturing specializes in precision Swiss Screw machining. Â The application was a custom aftermarket part for a Savage Muzzleloader.
Built by Savage Firearms, and widely held as the best in its class, this muzzleloader had one specific part experiencing wear after firing approximately 20 rounds; the vent-liner.  In the Savage muzzleloader, when the trigger on the firearm is pulled, the primer charge ignites and travels through a .031 hole in the vent-liner, and then into the combustion chamber.  The main powder charge then ignites, propelling the projectile.  All this happens in a millisecond, and in that instant the vent liner experiences a short blast of gas at over 2000°F and 40,000 PSI. As a result, the vent-liner erodes, causing an erratic, inconsistent burn of the main powder charge, affecting the accuracy of the firearm. Dave realized the need for a better vent-liner.  Velocity variation occurs when the through-hole erodes from .031 to .035 inches, explains Dave, so there is not much visual difference.  Being a shooter himself, Dave is keenly aware that to a discerning target shooter and hunter, any variation in a firearms performance can amount to a frustrating day at the range and missed opportunities in the field.
After considering Millennium Manufacturing’s proposed aftermarket part, Solar’s Corporate Metallurgist, Don Jordan, made a recommendation for the preferred alloy and heat treat process.  Dave promptly made dozens of precision-machined parts in a variety of custom configurations, and these were processed to the desired properties at 91´«Ã½.  This included the use of HT-81 for part of the process.
Several weeks after the original samples were processed; Dave sent roughly 2,000 vent liners as a repeat order. Â He offered feedback describing the overwhelming success of the parts fired in test rifles: the Savage vent-liners are working very well. Â Two guys are testing them and they are at 5x the life of the factory item and still going strong – not sure when one will wear out. Â One tester has over 200 rounds through one and that is a lot of shots with a muzzleloader.
The application of Solar’s proprietary process to the Millennium Vent-Liner brings the benefits of today’s technology to the old world firearm, the muzzleloader.  The benefits are achieved with a small part that now has higher-strength, better resistance to thermal fatigue, and a significant reduction in erosion from combustion gases.  These age-old challenges in firearm applications have been overcome by careful material selection and precision machining, followed by advanced thermal processing at 91´«Ã½.