The AR-15/M4/M16 Stainless Steel Grendel magazines are constructed with the highest levels of quality that guarantees durability and longevity! The 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. Available Coatings: Our durable, wear-in, not wear off, coating (Marlube) was developed directly from our aerospace roots. These Marlube coatings offer supreme performance, protection, and lubricity for your magazine. The more you use it, the better it performs. These Marlube coatings offer supreme performance and protection both to yourself and to your magazine. Your #1 choice for reliability, durability, and superiority! 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