The Aero Precision M5E1 Assembled Upper Receiver is a partially assembled upper receiver for AR-10-style rifles, designed for builders who want a high-quality starting point for their large-frame firearm. As an assembled upper, it includes pre-installed components such as the ejection port cover and forward assist, simplifying the build process. It does not include the barrel, handguard, gas system, or bolt carrier group (BCG), allowing users to fully customize these components to meet their specific needs. Machined from 7075-T6 aluminum, the M5E1 Assembled Upper Receiver features Aero Precision’s Enhanced Upper Receiver (EUP) design, which integrates the handguard mounting platform directly into the upper for added strength and rigidity. This innovative design is compatible with Aero Precision’s Enhanced Handguards, providing a seamless fit and improved durability. The receiver includes a Picatinny top rail for optics mounting and is finished with Type III hardcoat anodizing for superior corrosion resistance. Compatible with DPMS High Profile components, the M5E1 Assembled Upper Receiver is an excellent choice for builders looking to create a custom AR-10 platform in calibers like .308 Winchester and 6.5 Creedmoor.