This precision gas cylinder piston is made to exact GI specifications with all critical dimensions individually inspected. The 420 stainless material and heat-treating operations are both certified to assure quality. The piston has a highly polished surfaced using a non-contact electro-polishing method that maintains tolerance on the critical diameter and does not "round-over" the edges on the grooves. The piston is hard coated with a gold colored Titanium Nitride (TiN) finish. This coating, often used on machine cutting tools, helps reduce galling and pitting and holds up better to the high heat and abrasiveness of gunpowder and primers. The resulting effect is a smoother action an improved life of the piston and cylinder. Technical Information: Grooved gas cylinder pistons feature a .030 - .040 wide groove running along the piston axis on the large diameter. The groove runs through the gas-port hole for the purpose of equalizing the gas pressure for a smoother more consi...