Product Description The CMMG Mk4/AR15 Upper Receiver Assembly in Armor Black is expertly crafted from aircraft-grade Billet 6061 T6 Aluminum and finished with a durable Cerakote Standard coating. This upper receiver comes with CMMG&';s ZEROED Polymer Dust Cover pre-installed and omits the forward assist, giving your AR15 build a sleek and streamlined aesthetic. An enlarged ejection port expands compatibility to a variety of pistol calibers, including 9mm, 10mm, .40 S&W, and .45 ACP, making it an ideal foundation for PCC builds as well. Compatible with CMMG MkG, MkGs, Mk10, Mk9, and Mk17 lower receivers, this upper offers versatile build options backed by CMMG&';s Lifetime Quality Guarantee against material and workmanship defects. Product Highlights Constructed from Billet 6061 T6 Aluminum for a lightweight yet rugged upper receiver platform Cerakote Standard Armor Black finish delivers outstanding corrosion, wear, and impact resistance CMMG ZEROED Polymer Dust Cover comes pre-installed for immediate, ready-to-build use Enlarged ejection port enables pistol caliber compatibility with 9mm, 10mm, .40 S&W, and .45 ACP Compatible with CMMG MkG, MkGs, Mk10, Mk9, and Mk17 lower receivers; backed by CMMG&';s Lifetime Quality Guarantee Specs Brand: CMMG Platform: Mk4 / AR15 Upper Receiver Material: Billet 6061 T6 Aluminum Finish: Cerakote Standard Color: Armor Black MPN: CMM55BA290AB UPC: 810097506329 Compatible Lower Receivers: CMMG MkG, MkGs, Mk10, Mk9, Mk17 Note: Not compatible with CMMG fixed ejector Radial Delayed Blowback BCGs Disclaimer: We strive to provide accurate and up-to-date product descriptions, specifications, and images; however, errors or omissions may occasionally occur. We are not responsible for any inaccuracies or discrepancies in the content provided. If you notice anything incorrect or unclear, please contact us so we can correct it. When in doubt, we recommend verifying details directly with the product&';s manufacturer.