Stainless Steel Body: Our AR-15/M4/M16 Stainless Steel Magazines for 6.5 Grendel / 6MM Arc / .22 Arc / 338 Arc are constructed with the highest levels of quality that guarantees durability and longevity, and that's just what you get with this magazine. Our magazines are manufactured 100% start to finish in the USA using ".020" gauge 410 Stainless-Steel Alloy that is heat treated for superior strength, and lasting endurance. Their Stainless-Steel construction means they won't swell in heat or crack in the cold, making a more reliable alternative to polymer magazines. This is done all while maintaining that undeniably good look. Assembly Components: 410 Series Stainless Steel Body, Heat Treated Chrome Silicon Springs Enhanced Anti-tilt Polymer Followers with PTFE 300 Series SS Floor plate with Black Oxide Coating for Corrosion Resistance