From The Manufacturer/Wikipedia/People Smarter Than Us:
The Stainless Steel Mil-Spec is built on a full-size frame and slide. The pistol is made from stainless steel, which has a polished finish on the flat surfaces and bead-blasted matte finish on the rounded areas. The 5 inch barrel is match grade and made from stainless steel. The slide features slanted serrations on the rear only.