Case Studies
The Ruger Super Redhawk .454 Casull is one of the most powerful commercially available revolvers in the world, and a classic study in creative materials management and design.
This big-bore handgun, developed by firearms manufacturer Sturm Ruger & Co., Inc., Southport, CT, was designed from the start to withstand the very high stresses generated by the .454 Casull cartridge. The .454 Casull is one of the most powerful revolver cartridges made.
Wilderness guides, hunters, fishermen and experienced shooters use the powerful sidearm to hunt dangerous game such as brown and grizzly bear, elk, and jungle cats. With this revolver, a skilled marksman can drop a large animal at a distance of up to 200 yards! In addition to big-game hunting, the Super Redhawk .454 Casull is also used for target shooting at metallic animal silhouettes.
The massive, high strength frame of the rugged, double-action revolver has been key to its reliability and durability. More particularly, the specially designed cylinder and barrel, made from state-of-the art aerospace alloys, have been critical to its outstanding performance.
The Cylinder
Ruger's goal was to develop the firearms industry's first and only six-shot revolver in a .454 Casull caliber. Designers started with the proven, rugged .44 magnum (mag.) platform, planning to step it up to withstand the higher pressures produced by the .454 Casull cartridge.
The highest chamber pressure created when firing a .44 mag. revolver is about 42,000 psi. That compares with approximately 62,000 psi pressure generated when firing a .454 Casull revolver. Consistent with the difference in power, the larger caliber weapon has about 54% more recoil than the .44 mag. revolver.
Since the chambers in the cylinder had to be larger to accommodate the larger cartridge, some of the cross sections left between the chambers were reduced in thickness. These somewhat thinner walls had to withstand essentially 50% higher pressure than the original walls before redesign. This posed a materials challenge for the existing alloy in use.
Undaunted by the challenge, President William B. Ruger, Jr., instructed his design team to use the best materials available to make the six-shot .454 Casull handgun the latest success in the Ruger line of durable, large caliber revolvers.
Ruger first tried making the cylinder from stainless Type 410, a hardenable martensitic stainless steel generally suitable for highly stressed parts, such as Ruger's other revolvers. This grade simply would not hold up for any extended length of time during firing of the higher pressure proof rounds required for the .454 Casull.
The company then asked a regional metallurgist from Carpenter Technology Corporation (NYSE:CRS) for assistance in selecting materials. He suggested that Ruger consider Carpenter's new Custom 465® stainless.
Custom 465 stainless, developed as a candidate for aerospace components, is a premium-melted, martensitic, age-hardenable alloy capable of about 260 ksi ultimate tensile strength when peak aged. In this condition, it also offers higher notch tensile strength and fracture toughness than other precipitation-hardening stainless grades. It provides, in addition, excellent resistance to stress corrosion cracking.
Ruger made a cylinder from Custom 465 stainless, then fired 50 proof rounds from each of six chambers (total 300 rounds) at 92,000 psi. This is nearly 50% higher stress than what is produced under actual firing conditions. The designers repeated this firing cycle numerous times and noted that the cylinder withstood all the proof firing without a scratch or sign of defect anywhere.
With this evidence, Ruger selected the Carpenter alloy for the chamber of its new six-round .454 Casull. No problems related to cylinder materials have been reported to Ruger from the field since the mighty revolver was introduced a year ago.
Ruger manufacturing personnel started with annealed, cutoff lengths of 1.875" bar stock from Carpenter, but found that the material had such clean microstructure that they could reduce its diameter requirements to 1.828", and save on material costs. A slight amount of OD turning and drilling of the pivot hole was done on a CNC screw machine.
A CNC horizontal mill was used to drill the chambers. Ruger held tolerance of 0.002" on the ID of the chamber holes and 0.001" on alignment of the holes to the cylinder latch cut.
Machinists achieved a good finish inside the reamed chamber holes. This finish was deemed good enough that the company considered eliminating the final roller burnishing operation.
After machining, Ruger heat treated the cylinders in accordance with the schedule suggested by Carpenter to optimize essential mechanical properties, particularly strength and toughness.
Nominal chemical composition of Custom 465 stainless steel is shown in the Table below.
Table I: Nominal Chemical Composition of Carpenter Custom 465 (wt. %)
The Barrel
Ruger had to deal with several increased power issues in designing the barrel for its new .454 Casull revolver. Designers were concerned with the throat erosion that might occur when the big cartridge would exit the chamber and slam into the interior surface of the barrel. They knew the higher velocity bullet would have greater impact force, causing high-velocity gas cutting and potential erosion problems. That potential could be magnified if the steel selected for the barrel did not have the correct microstructure for these new requirements.
The first material considered was stainless Type 410, the standard alloy used with great success for other revolvers in the Ruger line of revolvers. Ruger was able to gun drill a 0.480" dia. hole in a 1¼" OD x 19" long bar in 17.27 minutes at 1.1 IPM. However, the material was unable to meet the newer, more strenuous requirements for strength, ductility and corrosion resistance imposed by the higher pressure .454 Casull cartridge.
Ruger then tried 15Cr-5Ni stainless steel, which met all the design requirements but one. It was a "bear" to machine. It took 28 minutes to drill the same diameter hole through the same OD bar at the slower rate of 0.71 IPM. The company could not accept the much longer gun drilling cycle time.
Again, Ruger asked the same Carpenter metallurgist for assistance. He suggested trying Carpenter"s new Project 7000® 15Cr-5Ni stainless, which also has been used as an aerospace alloy, in place of the conventional 15-5 alloy.
Carpenter Project 7000 15Cr-5Ni stainless is designed to offer improved machinability and with it, the opportunity to reduce part costs, cut cycle time and increase productivity. It has been made available as a "drop-in" replacement for the conventional 15-5 alloy in applications where improved machining productivity is desired.
In its trial runs with the Carpenter alloy, Ruger found that it was able to reduce its gun drilling cycle time by 20%. The Project 7000 stainless grade from Carpenter, in fact, matched the cycle time of the stainless Type 410, while improving tool life significantly. The vacuum melted, PH stainless also has excellent transverse mechanical properties to resist the higher stresses produced by the new cartridge.
The hole in the barrel, with a diameter tolerance of 0.002", is obtained by a deep hole drilling operation. The gun drilling is followed by reaming to obtain a finish. Each blank, starting at 1¼" OD x 19" long, is hammer-forged over a mandrel to become 1.171 OD x 23-7/16" long. The rifling and final diameter is formed during the hammer-forging. The forged length is then cut into three 7½"-long gun barrels.
All barrels that had been made from the new Carpenter alloy passed Ruger's rigid endurance tests with flying colors.
Typical analysis of Project 7000 15Cr-5Ni stainless is shown in Table II below.
Table II: Nominal Chemical Composition of Carpenter Project 7000 15Cr-5Ni (wt. %)
Overall, leveraging Carpenter’s metallurgical expertise, diverse product offerings, and premium alloy technologies helped Ruger identify the proper solutions to push the boundaries of their revolver product line.