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To contain the pressures generated by a handgun cartridge that makes Dirty Harry’s famed .44 Magnum almost look like a cap-gun, a leading firearms manufacturer turned to high-tech metallurgy to meet strength and machineability targets.
The older .44 Magnum cartridge is a high powered handgun chambering, capable of firing a 300 gr. bullet at 1,250 ft./sec. and delivering 885 ft.-lb. of energy at 50 yds. The .454 Casull, however, will throw a 300 gr. bullet 1,650 ft./sec. and impact a target at 50 yards with a substantial 1,455 ft.-lb. of energy, close to double that of the .44 Magnum. As the base platform for this new chambering, Ruger started with its proven, large-frame Super Redhawk revolver. A double-action design, this revolver has a reputation as a rugged firearm, capable of handling high-pressure loads. However, Ruger designers had concerns about the revolver’s ability to cope with the energy of the .454, especially in a six-shot cylinder. Although the Super Redhawk was commonly chambered for six .44 magnum rounds, designing a six-shot cylinder for the larger caliber Casull round meant a cylinder with thinner cross sections between cylinder chambers. In addition to the Casull’s larger diameter, the pressures the thinner cross sections would have to contain were significantly higher. A standard .44 magnum round produces chamber pressures of approximately 42,000 psi when fired. The .454 round produces pressures of about 62,000 psi, almost 50% more pressure. Consistent with the difference in power, the .454 round has about 54% more recoil than the .44 magnum. Ruger first tried making the cylinder from its traditional cylinder material, type 410 stainless steel. This material, a hardenable martensitic alloy, is generally considered suitable for highly stressed parts. However, this grade would not hold up for any extended length of time during test firing of the higher pressure proof rounds required for the Casull. At the suggestion of Humberto Raposo, a regional metallurgist with Carpenter Technology, Ruger tried a relatively new alloy that was originally developed for aerospace components, Custom 465® stainless. A premium-melted, martensitic, age-hardenable alloy, it is capable of 260 ksi ultimate tensile strength when peak-aged. In this condition, it also offers higher notch tensile strength and fracture toughness than other precipitation-hardened stainless grades. It is designed to provide excellent resistance to stress corrosion cracking. Machining the Alloy A cylinder was made from the Custom 465 alloy and subjected to firing 50 proof rounds in each of the chambers. Proof rounds are substantially different than normal, commercial hunting rounds. Proof rounds generate about 92,000 psi compared to 62,000 psi of commercial ammunition. Repeating the proofing cycle several times, Ruger engineers noted that the new alloy cylinder showed no signs of defects anywhere. In production, the cylinders start with cutoff lengths of 1.828" bar stock, which are OD turned on a computer numerical controlled (CNC) screw machine that also drills the pivot hole. The six chambers are drilled on a CNC horizontal mill and held to 0.002" on the chamber IDs and 0.001" on alignment of the chamber holes to the cylinder latch cut. With the ID finish achieved on the chamber holes, Ruger is considering eliminating a final roller burnishing operation. Following machining, the cylinders are heat treated to optimize strength and toughness. Challenges of dealing with the high pressures and power of the .454 Casull cartridge did not stop with the cylinder. Ruger designers were also concerned about throat erosion that might occur when the big .454 round would exit the cylinder, jump a small gap, then slam into the interior surface of the barrel. Because of the high velocity of the bullet and the high-velocity gas cutting, there were potential erosion problems that could be magnified if the barrel steel did not have the correct microstructure. Again, type 410 stainless, which had proven its capabilities as a barrel steel in other high-power Ruger revolvers, was the first choice. A 1¼" OD x 19" bar was gundrilled to a bore of 0.480" in 17.27 minutes at 1.1 ipm (inches per minute). This material, however, was unable to withstand the increased demands for strength, ductility, and corrosion resistance. A new alloy, 15Cr-5Ni stainless, was then tried. It met all of the design requirements, but was a “bear to machine,” according to Ruger sources. At a slower rate of 0.71 ipm, a 0.480" hole required 28 minutes to drill in the chrome/nickel alloy. This machining time was unacceptable. Again, Ruger consulted with the metallurgist who recommended Carpenter Project 7000® 15Cr-5Ni. The new steel was developed as a direct, drop-in replacement for the previous steel, but provided improved machineability. Using the Project 7000 stainless blanks, gundrilling time was reduced by 20%, matching the Type 410, and improved tool life. Once drilled, the 1¼" OD x 19" L blanks are reamed to finish, then hammer forged over a mandrel to become 1.171" OD x 23-7/16" L. Rifling is formed during the hammer forging. These forged blanks are then cut into three 7½" L barrels. With the new stainless alloys, Ruger has developed and markets the only production, double-action, six-shot revolver capable of handling the high power .454 Casull cartridge. Carpenter Technology Corporation Alloy Compositions Provide Machineability The two stainless steel alloys from Carpenter Technology that allow Ruger to contain the pressure of the .454 Casull cartridge are proprietary steels. They are designed to deliver specific performance and offer improved machineability. For most Modern Applications News readers, the information in the main article is sufficient. It is like telling you what time it is. We understand, however, some also want to know how the watch is built. For those, here are the compositions of the steels used by Ruger. The nominal chemical composition of Carpenter Custom 465 stainless is: carbon 0.02% max., manganese 0.25% max., phosphorus 0.015% max., sulfur 0.010% max., silicon 0.25% max., chromium 11.0 – 12.5%, nickel 10.75 – 11.25%, titanium 1.50 – 1.80%, and molybdenum 0.75 – 1.25%. The typical analysis of Project 7000 15Cr –5Ni stainless is: carbon 0.07% max., manganese 1.00% max., silicon 1.0% max., phosphorus 0.030% max., sulfur 0.015% max., chromium 14.00 – 15.50%, nickel 3.50 – 5.50%, copper 2.50 – 4.50%, molybdenum 0.50% max., columbium 5XC –0.45%, tantalum 0.05% max., and iron balance. - April 2001 |
Known as a manufacturing innovator among firearms companies, Sturm Ruger & Co., Inc. (Southport, CT) has, again, demonstrated its reliance on technology to solve design and production challenges. To produce a six-shot revolver economically in the extremely powerful .454 Casull caliber, Ruger had to change from its usual stainless steel alloys to two new steels from Carpenter Technology Corporation (Reading, PA).
Although a few manufacturers produced five-shot revolvers in this caliber, none produced the traditional “six-shooter,” primarily because of challenges in containing the chamber pressures developed by the .454 Casull, one of the most powerful handgun cartridges in the world. High-power, large-caliber revolvers are favored by wilderness guides and hunters for efficiently dealing with dangerous game such as brown or grizzly bear, large jungle cats or game animals like elk. With a revolver in this caliber, a skilled handgun hunter can engage game at up to 200 yd.