The SRH utilizes a special alloy stainless. I've pasted part of an article about this alloy:
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 Humberto Raposo, a regional metallurgist from Carpenter Technology Corp., 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 about 50 percent higher stress than that produced under actual firing conditions. The designers repeated this firing cycle numerous times and noted that the cylinder successfully withstood all of the proof firing without a scratch or sign of defect anywhere.
